Aristotle to Zoos: A Philosophical Dictionary of Biology

QA-TOZQ°S RISTOTLE

c\A-

RISTOTLE TO

ZJ

A Philosophical Dictionary of Biology

&

P. B. MEDAWAR J. S. MEDAWAR

HARVARD UNIVERSITY PRESS

CAMBRIDGE,

MASSAC I ll.'SEvITS

1983

PREFACE Harvard University Press, with I’etcr Gay's polished l%2 trans¬ lation of Voltaire’s Philosophical Dictionary as bait, invited us to embark upon a “philosophical dictionary of biology”; but where Voltaire had taken the whole world for his canvas, wc were to confine ourselves to biological topics retaining Voltaire’s format and if possible some of his espi ii , Wc hope our Aristotle la Zoos title does not promise, by its A to L format, a completeness of treat¬ ment to which we did not aspire. This work is philosophical only in the cozy domestic sense of being leisurely', relaxed, and reflective, There is no philosophy in it of a kind that could be thought to exemplify the Nalurphilosophit so popular in Germany in the nineteenth century a form of sci¬ entific belles (cures with a truly dismal track record for making sense of the puzzles in which biology abounds. It was to Naturph ihsophie that we owed the supposed existence of the very simplest and most remotely primeval of all orga¬ nisms the Moneta consisting only, as the prevailing nature-phi¬ losophy required, of naked protoplasm, it was to nature-philoso¬ phy, too, that we owed the conception that the skull of vertebra ics is Ibrincd essentially by ihc fusion and adaptive remodeling of the anteriormnst vertebrae, What a shame that Thomas Henry Hux¬ ley, whose expert hatchet job on this theory of the skull was the subject of a famous Croonian Lecture at the Royal Society in 1858, should have been so far taken in by Ernst Haeckel’s Alonera as to Have discovered a specimen of the group in a deep Atlantic dredging. The spirit of Naturphitosophie, moreover, shines out of the mis¬ conception that cancer cells arc essentially embryonic cells which, having escaped the discipline of differentiation, persist anoma¬ lously into adult life, later taking wing, so to speak, as malignant growths. All experienced biologists will share our anxiety lest the

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I’KEKACli

“philosophical" element in our dictionary should be construed in this deeply erroneous sense, On the other hand, this is not a reference book and not a dic¬ tionary of explanations and definitions. There is no need for such a work so long as the Pmguiti Dktiomty of Biology, a little master¬ piece of expert knowledge and skillful writing, is still in print. And it has reached its tenth edition in 1983. We include a number of definitions, it is true, if only to make an evolutionary connec¬ tion with a dictionary of a soil more ordinary than Voltaire’s, but these definitions are grouped under the subjects upon which they bear. Personal taste turns us from the major innovation of the En¬ cyclopaedia. ftritannica of 1771: the inclusion of very lengthy general articles dealing with whole sciences, to which seekers after partic¬ ular information are repeatedly referred. We feel that anyone who, curious or fearful, looks up spina bifida wants to be told what it is and does not wish to be referred to a treatise on embryology,

Perhaps the most famous passage in Voltaire's dictionary comes in the chapter “Tout est hicn, which contains the black theodicy beginning “Father God wishes to expunge the evil from this world and cannot; or lie can and does not wish to; or he nei¬ ther wishes to nor can.1' The entire passage was quoied by Vol¬ taire from a treatise concerning the wrath ol God by the fourthcentury church father Laetaniitis, who professed to have had it from Epicurus. Voltaire's contemptuous dismissal of Lactantius’ attempt to controvert the implications of this passage makes us think that Voltaire would have had little patience with the kind of theological humbug brought to the attention of the world by the Reverend Lord Ibidgewater, whose persuasions we shall con¬ sider in our text. If the present book is not for reference and not for looking up things, what and whom is it for? ft is for browsing. For the best results the reader must abstain resolutely from learning anything he or she does not want to know and must exercise at all times the reader's liberating privilege skipping. Among the educated audience we envisage might be biologists, sociologists, psychologists, and other members of that increasing population of relleetive people who sec in biology the science most relevant to (he understanding and melioration oT the human con¬ 1

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dition. vi

PR K PACK

Wc net grateful (o the following for pcrtnfksitifi io reproduce i hi-tfigures and photographs that appear in the (CM: to the Science M risen in, London, for (he figures, illustrating rfic three-dimen¬ sional geometric realization of :i number of algebraic functions; to Clarendon Press for the ill LJSI mr ion oft lie Gonipertz i auction and its principal derivatives; to the Royal Society of Londpn for the i [lost rat ion of how curves of growth may be con founded bv curves of distribution; and to Cambridge University Piess for the figures Imiu Sir D’Arcy Werttfoirth Thompson’s On Grtxvth and Fdffrt. It is a pleasure also to Accord our special indebtedness to our lit¬ erary assistant, Mrs. Joy Heys, for her assistance in preparing die manuscript and to Vivian Wheeler, senior editor at Harvard University Press, for her scrupulous editing and ordering of our

enatruscript, P.B M. .|,S M.

vii

CONTENTS Adapt at ion

1

Adrenal gland

Art

26

At ayjjm

Age distribution

Aggressive instinct

4

Aging

5

Albinism

a

Allergy

6

Allomct nr growth Akruisitt

LL

Ann no acids

12

Aniph ioxuS

L3

Anabiosis

14

Anetiocphaly

Ll

Bacteriophages

32

Barnacles

33

Behaviorism

(1

Bllhar/iasis

'if,

Bioengineering

46

Biogenesis Biology in medical

lils

education

39

Blood and its circulation

12

Cl

hi

aikcc

Carotid artery

50

L.ri

Cell theory

56

Antibiotics

20

5!

ApHcholineslerases

11

Anilgens and antibodies

2i

Centrifuge Ehan.ee and fandomness Chicken and egg

Apes

21

Chimera

54

Aquaculture

35

( Ihordat a

55

Archaeopteryx

36

Chromosomes

56

Aristotle

26

Clones

59

Animali and human

obligations

52

55

CONTENTS

Comparative anatomy

ep

Forte ol mortality

Hit

inhibition Sp>ronary artery

61

t’oirii and mathematics

102

fil

Frauds

107

Creationism

fij

Curare Cybernetics

63

Goipcl

61

Definition of life and Other

terms

66

Genet id

109

sell

Genetic and embryolugk terms

I to

Genius and insanity

129

Germ layer theory

129

Good warm land

131

tin

Demography

67

Design, argument from

70

Dmvn's syndrome

71

Great chain of being { Iroup selection

Ecology

73

Growth, ijtws

biological

134

of 136

Electrophoresis

73

Embryonic axis

7}

Hierarchy

m

hoboed nc gland

76

I fisloneism

1 13

Enzymes

7(1

Holism

! It

Epi t helium

79

Homology

i

Errors ol nature

79

Huntitrs;toil 's chorea

It')

Ethology

ti2

Hypothalamus

1 If J

Eugenics

fiG

Hypothesis -and theory

HS

Eutarybies

95

Euphonies

92

Illness

132

Evidence of evolution

93

IniEiumity

13,1

Exogcuet i e hered i i y

91

Immunologic Siirydllÿfce 136

Fertility

93

Figures of speech

99

Fitness

Mill

Individuality

Infertility and remedies

Instinct

n

137

its 158 160

CONTENTS

Interferon

162

Natural selection

m

Invert cbÿai a

IK1

Mature ami HUM iÿrje Neo-Darwinism

191

196

Nco( L-ny

199

Nerve gases

2n

164

King crab

] 67

Lamarr k ism

J66

Nerve impulses

am

Language

! 7(1

Nuclei acids

20 1

Lcnuni tigs

171

Life table

171

Ordci

204

Lungfish

172

in biology

Orders of magnitude Origin of life

2Qfy

m

Ornithology

2119

Lymphocytes

1 74

Ein licnogcnesis

21 l

Lyscnkoism

176

Malaria

Lymphatics and lyni[>!i

nodes

20!!

179

Phenylketonuria Fi Itdown skull

214

Man s place m nature

180

Pineal body

2V5

M eios is Mcmt Metabolism

I H2

Poiesis

2 1 .7

182

Population growth and

Mimicry

184

Missing links

1 87

M itoehnndria

1 ft j

Mitosis

186

Molecular biology

186

Mollusca

21 1

control

216

Primates

218

Proteins

21 !l

protoplasm

220

ProtOfcoa

2‘2\i

PtemdiicI yl$

221

189

Recapit u Un u m

227

Monotremes

196

Rcdnÿi ion iam

227

Mules

191

Reflex

232

M yaat benia gravis

191

Rhesus factor

233

m-i

QOHTENTS

Sense organs

235

Sessile animals

-j:i7

[ bet more gul at ion

Sexual cycles

237

TissSjfe culture and

Sexuality'

238

Sickle-cell anemia .Sociobiology

2W

Soma Sptx:i licit y Spina bilida Spontaneous general ion

242

Term ijfokigy storage

2i)7

25a 260

Toxins Trans form at ions

263

Transplantation

370

24 I

Vaccination

273

244

Viruses

375

243

Vitalism

27.3

Spores

246

Vitamins

277

Sweating

246

Symbiosisÿ

247

Water

270

Woodger’s paradox

2Bl

246

Worm

282

fty pHit is

250

Zoos

2W-I

Taxon

262

1 ndex

287

240

Sympathetic nervous system

Teleology

235

Teratology

256

264

cAT°2°°S RISTOTLE

ADAPTATION This word used in biology in several different denies, (he con¬ text? of which arc so different that they are not likely to give rise to mistmdersiandmgs. Adaptation may refer to the transformation occurring in the course of evolution that fits an organism to its habit or habitat (the wings of birds adapt them to flight and (be snout? of anteaters adapt them to rating insects); in a sense all evolution is ad¬ aptation. The word also refers to a change in the life of an individual or¬ ganism that enables it to cope better with the hazards tb which it? environment may expose it; the formation of corns or calluses where a shoe rubs is one such an adaptation, and the formation of art andbody against an infectious organism is another; again, at low oxygen tensions a? at high altitudes the number oT red blood corpuscle? increases, and repeated exertions enlarge the muscles that perform them. Adaptive changes of this kind are not imprinted on the gemmic and therefore are not heritable. Adaptation in the context of serrsation refer? to the fact that a prolonged and uniform sensory stimulus eventually ceases to give rise to a sensory message; thus someune who goes into a room containing a bowl of roses may smell them at first, but then be¬ come unaware of them. Once this process of sensory adaptation has occurred, no effort of attention can call rhe smell to mind, so this is quite unlike our unawareness of the ticking of a dock, which an effort of attention can at once recall to mind. It is a pop¬ ular fallacy that chewing gum regains its flavor if removed from the mouth and parked, sav, under a chair. What is regained is not the flavor but the ability to lasic die flavor a3 sensory adaptation wears off.

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ADRENAL

t;iANU

ADRENAL GLAND

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The adrenal is an endocrine gland one that liberates its secre¬ tory product directly into the blood or lymph, instead of into a duct which transports n elsewhere. It is in some ways an exem¬ plary gland, tor it illustrates especially clearly a number ol func¬ tional, evolutionary, and developmental characteristics found in endocrine glands generally, I’hc adrenal is a paired organ, somewhat diffuse and untidy looking iit lower vertebrates, but in mammals a compact, paired organ lying at the anterior poles of the two kidneys. The adrenal gland is composite in origin, as are many other endocrine glands, Indeed, the two components of the gland in mammals are entirely distinct in origin and function. The central core, or medulla , is essentially a modified ganglion (if the sympa¬ thetic nervous system. Tile adrenal medulla secretes adrenaline (epinephrine) and noradrenaline, the effects of which are, under¬ standably, the same as those brought about by general sympa¬ thetic stimulation: cardiac output is increased and the blood ves¬ sels of the brain, retina, and kidney are contracted, while the blood vessels in skeletal muscle lend to dilate. The psychological effects are familiar to people who have had injections of local an¬ esthetics for dental operations. To discourage local bleeding, such anesthetics often incorporate adrenaline in quantity sufficient to give the patient feelings of apprehension, restlessness, and unease superimposed upon reelings of the kind so readily stimulated by a denial operation, or the prospect of one, 'I'hc outer shell of the adrenal gland the adrenal cortex may arise in development from the first set of kidney tubules to be formed in life, the so-called pronephros. The cortex, which unlike the medulla is essential for life, is concerned with the regulation of minerals in the body, especially sodium salts. Removal of the ad¬ renal cortex or its destruction as a consequence nf infection or injury—causes rapid salt depletion. I’he effects can be fatal unless the victim receives injections of the natural secretions of the gland (including aldosterone, corticosterone, hydrocortisone or cortisol, and other related substances) or of substances exercising the same action. Because the symptoms of withdrawal of its secretions in¬ clude a genera) enfecblcmcnt and diminished resistance to stress,

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2

ACK DISTRIBUTION

it in generally assumed that the cortisone-like secretions of Jjhc ad¬ renal cortex are essential for ihe normal functioning of die body, par lieu lari y die integrity of the skeletal and supportive tissues and resistance to stress.

Thai part of l be cortex which is responsible for the secretion of cortisone-like substances is under the control of a secretion of the pituitary gland named, in accordance With the usual convent iom adrenocortical roph in (ACTH for short). When the adrenal cortex is in working order, injection of ACTH to increase its output is preferable to injection of the cortical hormones themselves. The con iso tie- 1 ike steroids are sometimes referred to as ‘'anabolic’" be¬ cause they promote anabolism and in high doses in ay increase muscle volume considerably, a property taken advantage of by athletes such ps weight lifters, especially in countries which regard victory in competitive games as evidence of the superiority of their political order.

AGE DISTRIBUTION A pop td a tiou has a structure not merely in space (its geo¬ graphic distribution) but also in Lurie, lor two populations may hare; verv different compositions with respect to the ages of their members. The age distribution is shaped by the prevailing death rales and fertility rates; only if the same regimen of both has been in force for many generations docs the age distribution adopt a sta¬ ble charade*; one which would be reestablished after temporary fluctuations or disturbances due to migrations of population or to wars and the like. The age composition of a population is profoundly important politically because it is the principal (aetor that determines the social burdens imposed by education, if stale aided, and old-age pensions, if granted- It may also affect the political temper or veil¬ ing behavior of the population because of the widespread but probably erroneous view' that the young, being hotheaded, will favor liberal or radical policies and vote accordingly, whereas the older, having become set in their ways, will be in Favor of the sta¬ tus quo, As Georges Glemeneeau, Premier of France (1917- 1920),

3

AGG R RSS1V R I NSTI N CT

once said, L'A man who is not a socialist at twenty lias no heart; a man who is still a socialist ill forty lias no head.'' We have little doubt that sociological research would find the grounds to prove

both of these beliefs illusoryIt can be very misleading to compare two populaiions with re¬ spect to, say, fertility or mortality if their age distributions are widely different. Mortality from cancer nr any other disease with art agc-relaLed incidence in different countries can be compared only if the incidence of mortality in the two countries is referred to a certain standard age distribution: for mortality in one coun¬ try may be higher than in another stinply because it lias a higher proportion of older people. It was his disregard of considerations such as these that led David Livingstone to formulate the wellknown half-truth that “cancer is a disease of civilizationÿ -A pop¬ ulation may increase in number by the accumulation of members beyond reproductive age, while at the same lime its power to re¬ produce itself maybe in decline.

INSTINCT People who speak of "the aggressive instinct’1 (few professional biologists arc among them) arc usually aggrieved and resentful when it is pointed oui to [hem that there is no such thing; that is to say. ihat there is no ktnd of tjrivfc or tippet tint; behavior that is assuaged or discharged by aggressive performances. There art;, however, aggressive dements in a variety of kinds of instinctive behavior in defense of territory, for example, in sexual rivalry, and in competition lor food. Some of this aggression is known to ethologists to be bluff- -to be a kind of warning demonstration or saber raitle that may achieve without risk to the combatants all that real aggression would do. There is no subs Lance whatsoever to the argument that, because “man is an aggressive animal1’ and ‘SOLI can’t change human nature,” wars between nations, are the inevitable consequence of aggressive instincts. Educated people do not have to refer to ethological papers before rcbtiiiing these trite propositions. In deed, such phrases are now almost univer¬ sally taken to mark an especially low level in conversation or dis¬ cussion. AGGK1LSSIVF,

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4

AGING

Although taken literally '‘aging’* merely means growing older, it seldom used without the connotation often distinguished in professional speech by use of the term senescence the progressive deterioration of bodily and pftMwi namxs that accompanics growing older. Attempts have been made From time lo time lo represent senescence as a pathological process, vet its char¬ acter and pattern of onset in human beings and domestic animals are such as to leave one in very little doubt that ii is in reality a natural process and of a piece with development, of whirl i it is

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faculties

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the closing episode. When does senescence begin:1 Examination of ntir own condi¬ tion tempts ns lo answer; ‘‘after a period of growth and matura¬ tion,” but in an arresting series of articles published in Popular Sci¬ ence Monthly (and republished as The Truhtan uf 'Age, Crowth and Death f London, lflG8]t the American anatomist Charles Minot gave a very different answer: aging, IK: declared, begins at birth. For tf we take the specific growth rale measuring the power of living tissue to reproduce itself at the rale it was itself formed as the best measure of "vitality,11 then it can be said with confidence that senescence does begin at birth because the specific growth rate falls from birth on. Minot’s initiative was the consideration that prompted us Lo describe as Minot’s Law the second of the two Jaws of growth we propound in the entry on GROWTft, uviVSipF utoi.otneAt,; this law affirms that die specific acceleration uj growth is n (wavt negative. There is, however, an element of preciosity saying that aging begins at birth: with less violence to conventional judgment it could be said that bodily del cri ora lion begins immediately alier thc actuarial prime of life, the brief epoch of life in which the force of mortality is at its minimum and our likelihood of living another month or day or year or minute is higher iha.ii it is at any stage before or after. This remark is a suitable cue for introducing the actuarial measurement of senescence, that which is almost universally adopted by students of aging. According to this scheme of mea¬ surement, senescence is conceived as that change in bodily struc¬ tures, faculties, or energies which increases the likelihood nf dying

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AtiiNt;

from accidental causes of random incidence, fur after the actuar¬ ial prime of life wc become ever more vulnerable. If people died only from accidental causes of random incidence and aging did not affect their vulnerability, then the force of mortality would be constant, but in reality it rises from the actuarial prime until the end of life. Although this is an apt and sensible scheme of measurement, it is not foolproof: it would be pedantry, for example, not to de¬ scribe the menopause in menstruating animals as an episode in the process of senescence; yet the menopause does not increase a woman’s vulnerability to mortal hazards, and to people of san¬ guine temperament it could be taken as an outward sign that one class of hazards has been outlived, namely those that have to do with pregnancy and childbirth. Likewise the graying of hair, uni¬ versally accepted as a manifestation of aging, is not accompanied by an increase in vulnerability. This of course might be taken to import that the graying of hair is not “really” a senescent change, but only a convenient outer manifestation of the contribution made to bodily deterioration by the accumulation of minute accidents and traumata such as radiation hits or physical injuries that destroy the melanocytes that feed their coloring matter into hair. Still, it is not very easy to distinguish between those senescent changes of the kind sometimes described as “programmed” (that is, dcvclopmentally “laid on”) and those that represent the cu¬ mulative sum of minute and individually trivial accidents or malfunciionings. Indeed, according to one theory of aging (the one that is particularly associated with the name of Leslie Orgel), such a distinction cannot be validly drawn, For senescence itself is the consequence of an accumulation of errors of transcription or translation from the genetic message specifying the synthesis of enzymes in the course of synthetic and vital processes generally. There is, however, one sense in which it is reasonable to de¬ scribe senescence as a pathological process: there is no known rea¬ son why it should have to happen. Biologists no longer accept (and indeed dismiss as Panglossism) August Weismann’s notion that senescence occurs for the benefit of the species, to remove the spent or worn-out animals that Weismann somewhat unrealisti¬ cally thought were cluttering up the environment and depriving 6

AGING mnntrous

nomenon,

vOungsLcrs of food and IcbcnsraiLin. W hat kind of phe¬ anyway, would make senescence an bbligative process?

One possibility would bit a determinate life span of cell lin¬ eages a limitation of the number of successive cell divisions through which a done of cells could pass. Weiscpanrt, curiously, believed that such a limit existed, Although he professed not to know why it should be so, a constitutional lack of quantitative judgment made him suppose that a cell might be confined to one thousand or text thousand successive divisions. Whereas he was not wholly wrong in principle, quantitatively he was very wide of the mark. Although wc all at one time believed that ceils could be propagated indefinitely in tissue culture, we now know that nor¬ mal cells have a finite lifetime and cannot be carried tit rough an indefinite number of cell divisions under any circumstances. The real reason why tin: flagrantly u n adaptive process of be¬ coming senescent rakes place is that from an evolutionary point of view it makes little difference whether it does or not, In the entry on H UNTI NGrphFs: OJfOKK/t (a genetic disease of dominant deter¬ mination, which makes itself manifest relatively late in life) we point out that most of its future victims could have had a family of ordinary SLJC before the disease appeared- This is probably true of all manifestations of senescence prominent or debilitating enough to be attributed to aging; tiles' occur during the postreP reductive period of life, after people or other organisms have taken whatever share of the ancestry of future generations could be expected of them. The force of natural selection is greatly at¬ tenuated; considered as a nonadaptive character, then, senescence cannot be opposed by the common selective forces and phased out of the genome of any species. This circumstance led to the advancement of the theory of aging especially associated with the names of If B. Medawa| and G. C. Williams, namely that aging is the consequence oT the aecumulaliott in the genome of maleficent genes, the ill effects of which do not become apparent until late enough in life for them to be virtually out of reach of natural selection, if we look at Huntington's chorea and a number of other diseases of late onset (such as familial intestinal polyposis, often leading to cancer) as eases in point, it is undeniable that the theory has some substance. It is a corollary of the theory and was indeed one of the consid-

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7

ALBINISM

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era i ions that led to its being propounded that senescence is es¬ sentially an artifact of domestication, This does not of course mean that domestication is the cause of senescence, merely that it is the unnatural state of affairs that allows senescence to become manifest by withholding from the organism the action of many of the agencies that in real life might easily have been fatal (priva¬ tion, starvation, exhaustion, or infection). Indeed, contrary to popular superstition, aged animals are something of a rarity in nature, where a savage exaction of mortality is the rule. Senescence, anyway, cannot be regarded as an epiphenuruenori of life: it is something we must live with. On the other hand, se¬ nescence is a physical change and there is no reason in principle why some means should not be devised to meliorate it. One of the great strengths of the ethos and scheme of manners implicit in puritanism is that judging from experience with laboratory animals, temperance (especially in caloric; consumption) is a very impor¬ tant— perhaps the most important agency for the prolongation oriife. Several investigators have recorded Lhai systemic adminis¬ tration of high doses of industrial antoxidanls brings about a sig¬ nificant prolongation of Life. This observation has not been wel¬ comed as rapturously as might at first be thought because of the uneasy suspicion that the aritoxidanls, which arc somewhat toxic, could act by diminishing appetite, thus reducing calorie con¬ sumption to the degree (hat tends to favor longevity. I'he mention of high doses of amoxidants systcmically administered turns the thoughts toward oral consumption of high doses of ascorbic acid (vitamin C), which, too, has its advocates the two chief oT whom, lively octogenarians, are alive at the time of writing.

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ALBINISM This is a disorder of the pigmentary system in which, with no diminution in cell number or change in disposition, there is an extreme attenuation of pigmentary function in the cells poten¬ tially capable of making pigment the melanocytes. Unmasked by black pigment, the retinas of albino people and animals, being very highly vascular, are bright pink. Without the protection of pigment, the retinal sensory cells are easily damaged, and albinos generally suffer severe defects of vision,

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B

ALLERGY

Albinism, or rather t tic dilution of pigmeisi of which it fepreseijts the extreme form, is genet icadly controlled and is to l>e found in ninny domestic animals such ns mice, rats, guinea pigs, horses, and human beings. In some cultures albino human beings have been regarded With superstitious awe, and white steeds much ad* mired. In so-called albino guinea pigs and Himalayan rabbits their condition, referred to as albinism, is in reality an cm rente dilution of pigmentation. These animals have the property that their points (paws, tips of ears and noses) darken in cool weather for reasons not yet uriderslood, because they look alike, albino rats arid mice are often assumed to be genetically uniform; in reality, albinism may conceal what would Otherwise be flagrant genetic diversity, This is a familiar (rap for inexperienced experimental biologists and psychologists. The latter, for instance, have often taken V\ isiar rats ta be as uni¬ form in genetic makeup as they are in color.

ALLERGY

An allergy is a miscarriage of the immunologic process in which something that begins as a protective device has deleterious consequences that range in severity from itching to sudden death. The allergies arc protean in their diversity, and not ail their manifestations or all the agents that can arouse them are yet known. Pretty much any nonseir substance that can gain access to an immunologic response center may be an allergen that is, an antigen that is a prime mover in an allergic response. The best known and most tiresome antigens arc the pollens that arouse hay fever and asthma, t he fungal spores that give rise to farmer’s lung, the mites in house dust whose excrement arouses ait especially in¬ tractable form tT asthma, the industrial chemicals that are forever arousing allergic dermatitis, and tint many antigenic foodstuffs such as eggwhitc and shellfish which are notorious for causing gastric pains and urticaria. Other grave offenders arc new medications or their veilides. substances such as antibiotics and especially the horse serums that contain antibodies to bacterial toxins- -aiiLidiphihcric serum and amitetanus scrum, lor example. (It has been cynically said tbat.

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9

Al.tJCJMETRIC GROW TH

considered as an allergen, horse serum has caused more deaths than have ever been prevented by therapeutic action of the anti¬ bodies of which it is the vehicle.) The liberation of histamine by a certain kind of white blood corpuscle during the interaction of an¬ tigen and antibody is responsible for the physical distress of pkylaclic shock; other such pharmacologically active substances arouse allergies of the so-called Arthus type, triggered by the meeting of antigen and antibody within the tissues. (Farmer's lung is a reaction of the Arthus type.) A theoretically important and medically useful form of allergy is the delayed-type hypersensitivity reaction. It is described as “delayed” to distinguish it from the rapidly developed wheal-andfiarc, which is caused by the injection into the skin of test quanti¬ ties of antigens that arouse allergies of the asihma/urticaria type. A hypersensitivity reaction of the delayed type, on the other hand, is characteristically aroused by the introduction into the tissue of antigens oT the kind that arouse cell-mediated immunity, Over a period of five to twenty-four hours swelling and reddening develop, accompanied by some pain or itchiness and as revealed under microscopy a congregation of white blood corpuscles (especially lymphocytes) within the tissues near the point of in¬ jection. The tuberculin reaction is an example: it is the basis of the Mantoux test, in which such a local skin reaction is aroused by very small quantities of extracts of tubercle bacilli in people who have or have had an active tubercular infection. Most allergies arc not so potentially useful as the Mantoux test; on the contrary, they are a significant source of malaise, discom¬ fort, or distress. Antihistamine drugs and adrenal cortical steroids arc widely used for the symptomatic treatment of allergies but, as ever, prophylaxis is best the avoidance wherever possible (and very often, of course, it is not possible) of allergens such as pollen, fungal spores, house dust, and sensitizing chemicals.

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ALLOMETR1C GROWTH

It is the merest truism that grow ing up is not merely a matter or symmetrical enlargement, that the adult is not merely the young¬ ster writ large. On the contrary, organisms change in shape as they develop, and inasmuch as this is an orderly and regular pro10

A [.TRUISM

cess we should expect IO find some orderly and perhaps simple re¬ lationship between the growth rate of one part of the body and the growl h rale of the whole or of another part. I’he “law*' of allomctry first proposed was that in grow ing up i he specific growth late of one bodily parE bears a constant ratio to l he specific growl h rale f>r another part. If x and y designate two parti! and stand also for their sizes, the sjvccific growth rales of the parts are respectively (1A) {dxfdl)=ÿ(ÿ grow strictly in proportion 10 each other, and that>' is gaining on x or alternatively losing ground as a is greater or less than unity. For a more general treatment of the problem of change of shape in development, the reader is referred to our entry On TRANSFORMATIONS. See also the discussion ofckomu, IAWSOK BLOLFJOKLAJ,,

ALTRUISM

Altruistic behavior is behavior that brings advantage to others than those who perform it, The connotation of disadvantage to the performer is not an essential part of the meaning, bul is rather a special properly called in evidence to show that behavior is gen¬ uinely altruistic and not motivated by covert sclf-intercsl. Altruism raises some very nice problems in the genetic theory of evolution by selection an entirely selfish process that depends upon a gene’s enjoying a net reproductive advantage over its al¬ ternative forms; but how can any gene have such an advantage if it disadvantages its possessor? One answer, which plays a crucially important part in the theory of sociobiology, is kin seizelion. Consider parental care, for example. To use woi’ds that might have come naturally to the late P, G. Wodchouse, a hen that be¬

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ll

AMINO AGIOS

broody is p an icu lari y vulnerable to a fox. or other predator that creeps up behind it wielding a. short length ol lead piping; how then can the genes (hat provide socially advantageous be¬ havior of this kind become established in the stock, as it is neces¬ sary and desirable ihat they should? The answer is that a parent that protects its young is at the same lime protecting those of its genes that are represented in the young. J. b. S, Haldane put it more pointedly in an aside recollected by John Maynard Smith: he said he 3wsis willing to lay down his life Tor two brothers or eight cousins. The genes promoting this highest form of altruistic be¬ havior (“Greater love hath no man , - .”) would have prevailed in the population and brought net rep rod tic Live advantage to their possessor’s genes even if their possessor had Lost hts lile. In such a case l he advantages or disadvant ages can be fairly easily quanti¬ fied, but some reports of altruistic behavior should be regarded with extreme skepticism, the most notorious being the widespread belief that in order to reduce their numbers and thus promote the welfare of the species as a whole, lemmings from time to time commit suicide in large numbers by throwing themselves tiff a cliff to drown. “If you believe that, you can believe anything/’ as the Duke of Wellington is said to have remarked to a lady who accosted him with the words "Mr. Smith, 1 believe?” I’he theoretic importance of kin select ion is that it lends a de¬ gree of credibility to the kind of evolutionary speculation em¬ bodied in socio biology. conies

AMINO ACIDS An amino acid is the budding block or monomer from which he protein molecule is constructed. It may he thought of as a compound formed by substituting an ammo (NTT-J group for one of the hydrogen atoms on [he carbon chain oT a fatty acid. Thus the substitution of an NH2 group for one of the carbons in acetic acid CHjGOOH, the characteristic acid of vinegar, yields the simplest amino acid, glycine; CHu\H2COOH. An amino acid (there are twenty different kinds) is effectively acidic or basic in accordance with whether carboxyl {COOH1 or amino groups pre¬ dominate in the molecule. i

J2

AMPHIOXU-S

AMPHIOXUS [’ll in zoologically fa mu us animal, of which the agreed generic name is now Bfanchwstoina (lanoeJet), owes its importance to being she modern represen tal i vc of the xuhphylum CtphahihnTdcita, which was surely ancestral to the vertebrates. Displaying in al¬ most diagrammatic form the defining eh a ract eristics of ihe group Chordata, amphioxus is an inch or two long and, like a modern automobile, is pointed at both ends (hence its older name, the syl¬ lable i&jr having the connotation of sharpness or acidity). Although it can swim, amphioxus nonrially lives in shallow seawater on a sandy nr gravelly substratum. Like its ancestor the sea squirt, it is a filter feeder, living on small particles suspended in the water current that passes through its mouth into a spacious pharynx, the antechamber to the gut. The pharynx is perforated by numerous slits through which the seawater escapes,, whereas solid matter is trapped on the walls of the pharynx made sticky by a mucous secretion from the median ventral groove, the endoslyle tit at is the precursor in vertebrates of the thyroid gland. The pres¬ ence of a forge perforated pharynx associated with the habit of fil¬ ter feeding h characteristic of chorda tes. Another chord ate feature is the elastic skeletal rod, the rwto(hf>td, that stretches from one end of the body to the other. The musculature consists of scgmcntally arranged muscle blocks also extending the length of the bodv. There arc no limbs, The central nervous system is of the usual chorda te pattern: a median dorsal tube sends motor nerve fibers to the segmental muscle blocks and receives sensory fibers that pass between the muscle blocks and enter the lube dorsally, The blood system, equally typical, is a median ventral con tract tie vessel propelling blood forward and up the sides of the pharynx in the gill bars that separate the gill slits. Circulation up the gill bars is assisted by a small “branchial” accessory heart at the base of each bar. One system is altogether atypical of chordaies. Anatomists were greatly surprised when the excretory system wras Shown to consist of little clusters of excretory cells, “flame cells” such as are found in several invertebrates. Aside from this one uncalled- for departure from (he chord ale canon, amphioxus answers so very well to what is expected of an organism ancestral to vertebrates 13

ANABIOSIS

ihai it would have been said to exist (or to have existed) even ifii had not been discovered and recoin i zed. iso much for [hr rich relatives of amphiOxus. Its poor relatives arc revealed by the possession of a pharynx and the filler-feeding habit, and even more so hy ns development; ior the earliest devel¬ opmental stages of amphioxuS arc almost identical to those of the sea squirt. There is another affinity too: the larva of amphioxust is curiously asymmetrical, the month Starting high up on one side of the front end of ihe body acid moving into its definitive position only by a complex rotatory movement of the entire branchial basket in relation to ihc notochord and muscle blocks. It has been suggested ihat this rotatory movement is homologous with the ro¬ tation of the pharynx in the embryonic sea squirt, a strange meta¬ morphosis that precedes its attachment to the substratum and causes mouih and anus to occupy their definitive positions in the

adult sea squirt.

ANABIOSIS Now obsolete, this term refers to the state of suspended anima¬ tion characteristic of tissues preserved by extreme eoldThc idea of preserving whole organisms in this why occurred lirst to John Hunter (1728-1793). “Ol ihe Heat ol Animals*’ desfcribcs liovy he tried (n freeze two carp, hoping that “ft might be possible to prolong life to any period by freezing a person ... I thought that if a man would give up the last ten years of his life to this kind uT alternate oblivion and action, it might be prolonged to a thousand years, and by getting hunseii thawed every hun¬ dred vcar.i, he might learn vvha! had happened during his frozen condition. Like other schemers, I thought T should make my for¬ tune by it; but this experiment undeceived rife" (from The Works of John Hunter, FR$} ed. ]. F. Palmer (London, 1835], vol. 1, p.

m

ANENCEPHALY Gross reduction in the size of the cerebral hemispheres .so often accompanies spina bifida that they are frequently classified to¬ gether as a single syndrome, ASB, Standing for anencephaly/ 14

ANIMAIiS

AMI)

HUMAN OBLIGATIONS

spina hilidn. It is a develop mental aberration to which the embryonic axis arc' especially Vulnerable, Abb is no1 in any ordinary sense a hereditary affliction, but for un known, possibly immunologic, reasons it does occur mure fret|uoni]y in women who already have a history of spontaneous abortions. ( hie embryologist ha* suggested that its higher frequency among Roman Catholics may he attributed to ihc use of the rhythm method of fertility com ml, which lends to result in late ieriiliicjitiou and (Ims in an abnormally long delay in activation of an egg cdl by (he ordinary process of fertilization. There arc pronounced variations loan place to place and from population to population, the incidence being notably high in Northern Ireland and father low7 in Africa south of (he Sahara, 1 hough epidemiologists tire al¬ ways on their guard against such comparisons because of the variation from place to place in the reliability of asceriainmcni. Congenital abnormalities generally offer no comfort to racists be¬ cause Some are more frequcni, others less so, in black than in com¬ parable white [jopuhnions. Although common sense suggests that anencephuly must he ac¬ companied by an abject diminution of mental capabilities, evi¬ dence is growing that ancnccphulics are capable of nianv intellec¬ tual powers though i to be the prerogative of the cerebral hemispheres. The faculties of the midbrain must not be under¬ estimated, nor (he functional plasticity of the brain. structures of dir

HUMAN OBLIGATIONS The word ‘'animal" is not mentioned in the Bible, but Jeho¬ vah’s rulings on the relationship between man and beast arc clear enough, Human beings were to have ''dominion over the fish of the sea and over (he fowl of the air, And river cattle and every creeping thing” (Gen. Iixsivii), A later verse goes on to reassure man nT “dominion over the fowl of the air and over every living thing that moveth upon the earth.” Plants rank low in the hierar¬ chy, for to all the animals meniioned Lress a ttonclotting Hind known as fftlim, which is normally free of contained cells. Although there are exceptions, arteries usually con mitt oxygen¬ ated blood under a pressure that is estimated by ascertaining with a simple apparatus ihc applied pressure necessary to occlude an artery and temporarily stop the blood Mow. Veins in turn contain dcoxygenated blood, which is. darker than arterial blopd the ex¬ ception being, of course, the pulmonary artery, which contains not-y el -oxygenated blood to be conducted to the lungs, from which the pulmonarv veins will return oxygenated blood to the atrium of the heart. Arteries generally have muscular coats, and it is the contraction of these coats ihni presents bleeding when small arteries are cut. Apart from red blood corpuscles, blood plasma holds in suspen¬ sion a variety of white blood corpuscles, or leucocytes, the most numerous among winch are the lymphocytes and the granulocytes of various kinds, which can ingest foreign parlicuiate matter such as bacteria (especially If (heir targets have been coated before¬ hand with antibody).

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42

BLOOD AND n;s CIRCULATION

1L is didicult nowadays in pul oneself in the position of those at one time believed that tile movement of blood is essen¬ tially Jin ehh arid How an advance and retreat- Thug it is easy tn underestimate the importance of the discovery of the circulation of the blood, a discovery' which by its sheer magnitude and by the style in which it was made earned William Harvey a place on the team of AH- Time Greats captained by Sir Isaac Newton, which counts among ns members Galileo, Datwin, and those few others who in their' time changed the direction of the flow of thnnghi. Although the Spanish physician Serve) us recognized the pul¬ monary circulation (from heart to lungs and bad again), Harvey went far beyond him in discerning !he nature of the pulse and the anatomic basis of the systemic circulation: he perceived, too, the function of the valves, the passive nature of the dilatation of the heart and indeed recognized all the fundamentals of Our present understanding of the circulation of the blood. Harvey discovered ail this by anatomic observation and by simple arid sufficient oliscrva lions the best kind. li is most unfortunate that in order to give countenance to a fa¬ vorite mystique having to do with cii ideal observation, and to make Harvey appear “scientific" in die style that John Stuart Mill and Ktirl Pearson believed to be distinctive: of science, Har¬ vey has been portrayed as an inductive scientist who, with no preconceptions whatsoever, made observations and conducted experiments from which he deduced die theory of the ei retd a lion of die btood. We believe that in reality Harvey nins< have had a clear preconception of the notion of circulation; So, far from col¬ lecting facts and piling up empirical observations, his experiments were exactly those that would have been carried out by someone testing an existing hypothesis. In si tort, Harvey was. much more o I a card-can Jyiug scientist than lit: is represented to be by those who have tried to claim he was ait induct iviSt who did no more than attend humbly to Nature's lessons as lie learned them from her own lips.

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—

The evolutionary history of bit Mid has been (lie subject of a number of romantic speculations, one of which was (hat blood Is essentially an evolutionary descendant of seawater and that its salty composition in mammals today reflects the salty composi-

43

BLOOD AND ITS CIRCULATION

lion of the sea in the era during which fish left the sea in colonize dry land. There would be spme substance to this notion if there was even the faintest likelihood that the blood of fish was ever in os mol it: and ionic equi librium With the seawater that surrounded them. There is a certain affinity between the sally makeup ol sea¬ water and that of blood; inasmuch as life must have begun in the sea, the metabolism of ceils most surer! y have evolved in relation to tin.1 inorganic constituents of the sea, especially sodium, potas¬ sium, calcium, and magnesium cations and chloride anions. The hypothesis of a marine origin of blood has been cited as an example of [met ism, that JS, the evaluation of scientific hypotheses by literary rather than scientific criteria a miscarriage of thought as offensive as scientism, the application of sup|>oscfJ!y sci¬ entific procedures to the investigation of matters on which science has no bearing whatsoever (P. B, Mcdawar, Pluto's Rspubth [Ox¬ ford, 19821, pp. fiO 61). The term “blood relationship” is a figure of speech for kinship, for genetic relationship. Although there is no foundation in theory or fact for t he belief that the cl laract exist iex of bli>od give a deeper insight into alfinities than the characteristics (T other tissues, be¬ cause of the accessibility and forensic significance of bfood, its properties are the ones studied most intently in problems having to do with identity, The methods of ascertainment are less often chemical than, immunologic, because immunologic methods have a higher resolving power and a high nr degree nl specificity tit ait any

other-.

It goes without saying that blue blood is not a sign of gcniility, nor red blood of fortitude and courage. Nevertheless, in some contexts the figurative meaning has wholly usurped the literal. "Sanguine’1 is never used today to signify blood -red, but only the cheerfully hopeful disposition to which a ruddy countenance is thought to bear witness. The word '‘optimistic” j$ fastidiously shunned by those reluctant to impute to the person to whom it refers a belief in some of the metaphysical consequences of the philosophy of Leibniz.

(CANCER The branch of pathology that has TO do with the study of cancer is called oncology (the prefix once- always relates to cancer, as in on¬ cogen or oncovirus). What we know about cancer is the accumu¬ lated understanding of many centuries of clinical observation and about a hundred years of systematic research. Some pathologists, oppressed by the enormous variety in cancers, their modes of growth, and the wavs in which they may be caused, deny that cancer is a clinical entity: it is not one, they say, bat many diseases of different origins and different behaviors, for which we should expect to devise a proportionate number of different treatments. While not denying any of this, we do not think we are yet knowledgeable enough to refute the more straightforward assumption that there is a commonality in the formation of all tumors and that therefore there is a fundamen¬ tal resemblance among them all, though it has not yet been dis¬ covered- This is not to imply that there need he any such thing as “the” cure for cancer. Individual tumors are sure to have distinc¬ tive properties, such as dependence upon specific hormones, of which it is often possible to take clinical advantage. In the accepted terminology of cancer the suffix ~oma usually refers to a nonmalignant growth or swelling: a corn, for example, produced on the dorsum of a toe by light-fitting shoes is an epithe¬ lioma, and the benign swelling of bone is an osteoma. When a growth of epithelium is malignant, it is referred to as a carci¬ noma; some purists insist that the word "cancer” should not be used as a generic term for all malignant tumors but should be confined to tumors of epithelial origin. Usage, however, is tending to annul these sematologieal niceties. The word "sarcoma,” for instance, is used For a malignant growth of skeletal, connective, or circulatory tissues, as in osteosarcoma, fibrosarcoma, lymphosar¬

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coma. 45

CANCER

A rapid growth rate is noi a universal characteristic; of tumors, nor is it the pro perl y most to be feared: it is the tnvasitfttuss of minors

that makes them simultaneously more dangerous and less

accessible

to

surgical

treatment,

Meiasku-is or the spread of the

tumor throughout the body from its place ol origin is another seri¬

ous tomplication. Eydri though cardiovascular disease: long ago became the prin¬ cipal cause of death of adults in the industrialized Western world, cancer still arouses more anxiety than any other disease. Lewis Thomas has called attention to the parallel between the dread of cancer and the dread of tuberculosis (“consumption1') that was prevalent at the turii ol the century and For a decade or more af¬ terward- The diagnosis of consumption too was construed as a death sentence, especially if the infection had spread throughout (he body. This attitude toward cancer is widely prevalent today: cancer, it is thought, is incurable, progressive, inevitably fatal, and never remits of ns own accord. These bclicis are not entirely accurate; cancers cart sometimes be cured, although admittedly not as often as is implied by articles in magazines whose editorial policy is doggedly optimistic in order not to alienate readers and adver¬ tisers alike. The coin bi nation of surgery with chemotherapeutic drugs Hors arrest the growl h of some cancers sometimes; still, there is nothing tojusnfy a sanguine prcsmnpl ion of success in all cases. Moreover, some cancers do undergo spontaneous regression, do dwindle away and disappear even without therapeutic interven¬ tion. This phenomenon, combined with the belief that many more tumors arise than ever become a clinical threat, has given rise to the widespread opinion that there is some natural bodily defense against cancer. Many biologists believe this, although the biological case for such a defense system's having evolved is rather weak. Unlike infectious disease, cancer has not been a cause of mortality great enough to have generated much selection pressure: it is large!v ti disease of post reproductive life tit at is, of a period during which (as explained in the entry AGING) the force of natural selection is greatly attenuated. What form could a natural defensive mechanism take? The consensus is that if such a mechanism exists It is in a general sense

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Iti

CANCER

immunologic and depends upon l he tumor’s Being endowed with or acquiring sufficient nonself properties LO be antigenic. In Inbo¬ rn torv animals tumorS caused liv oncogenic viruses and Oncogenic chemicals arc almost invariably antigenic and. often arouse an im¬ munity reaction strong enough to cause them to be rejected, that is, to dwindle away. It is less certain that this is true of the tumors described as *’spontaneous” because their causes are unknown, Applied cancer research is mostly a matter of seeking new Ettid butler antiproliferative drugs. The difficulty in principle is that none of thc.se drugs is cancer -sped fie. They retard the growth of proliferating cells but may themselves be oncogenic as \ rays and gamma rays are well known to lie. Because oi these draw¬ backs, the notion of an immunologic treatment is especially at¬ tractive but the results so far have been rat hqr disappointing One of the most interesting new areas of cancel research has grown out of the not ion |tf ampk&ia, As this notion is of metaphys¬ ical Origin, it may constitute an especially apt example nl Karl Popper’s thesis that far from being dismissed as so much non¬ sense, metaphysical speculation as a source of ideas is entirely ad¬ missible in science provided those ideas are exposed to the rigor¬ ous critical examination to which ail scientific notions should be exposed. In the nineteenth century in Germany natu re-philosophical speculation affected clinical pathologists as well as conventional biologists. Some pathologists thought Lherc was a deep-seated collection belwcen cancer celts and embryo cells. \\ ith ihe nenrone in mind, they reasoned that a cell’s ability tn multiply varied inversely with its state of differentiation: the more highly dif¬ ferent iaied the celt, the Jess able it was to undergo division (cells of the early embryo obviously can Einrl highly differentiated cells such as neurones obvlouslv cannot}. Because rancor rolls art' readily able to divide, they must, it Was argued, have undergone dediilerentiation anti reversion in ail embryonic condition. Cancers, Julius Cohn hr ini though t, developed from embrvonte LYcsts" or leftovers from embryonic rolls which because ol some misadventure had failed to differentiate and had persisted anomalously into adult life, This is a hypothesis long since ex¬ perimentally falsified, thougbone can understand its nature-phil¬ osophical appeal. Moreover, dedillcreniialkin does not occur:

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47

CANCER

cancer cells retain (heir differentiated properties and cont in nc to manufacture their characteristic secretory products. Ana¬ plasia, however, dues occur in a somewhat modified sense: cancer cells may manufacture anew substances produced in embryonic or fetal life by their own distant cellular ancestors, It is to this un¬ expected reawaken Ingand reactivation ol Irenes which functioned earlier in embryonic life that the word “anaplasia” is now ap¬ plied. In essence cancer research is based upon an attempt to find a clinically usable difference between a malignant cell and its nor¬ mal counterpart. Anaplasia is not the definitive answer to this problem, but it is l he closest approach so far. The phenomenon has aroused special ini crest, and a recent conference on fetal anti¬ gens in cancer convened by a charitable loun.dai.ion in London was attended by cancer research workers from nine different countries. Cancer research is by no means barren of ideas, as some seem to suggest When seeking excuses to reduce its handsome sub¬ sidies or diminish its standing in science. We believe that cancer will eventually be brought under control by the !u ['titer develop¬ ment and medical application of ideas current today. No one will deny the truism that the best way to cope with the cancer problem is not to get cancer, Jt should be a source of some rejoicing, therefore, (hat cur re tit expert opinion puts as high as percent the proportion of cancers that arise from exogenous, and therefore irt principle preventable, causes. We have in mind cancer viruses, industrial chemicals, ionizing radiations, ashes Los fibers, and many lood additives (preservatives, “improvers," col¬ oring matter, and flavoring). Although it is not always possible to equate the Sanctity of human life with Lite sanctity of profitable commercial enterprise, vigorous legislation is being enacted in both the Untied Slates and the United Kingdom to insist upon safeguards with respect to commercial use of potentially onco¬ genic chemicals, For the past cpiarier-cenLury the most valuable evidence relat¬ ing to the causation and control of cancer has conic not from the clinic or the laboratory but from epidemiologists in league writh demographers, the registrars of births and deaths. The culture hero of cancer epi dent in logy is the Pcrcival Pott who first demon¬ strated the connection between cancer of die scrotum and the ocmost

48

CANCKK

cupaiinn of chimney sweep. Reasoning similar in principle has subsequently established a connection between oncogenesis and radioactivity, between skin cancers and coal tar arid its distilla¬ tion products, between smoking and Jung cancer and more re¬ cently between cancer and deficiency of vitamin A and the caro¬ tenoids,

The order of magnitude of the sums spent to promote cancer research is hundreds ol millions of dollars, but the value of that research is not to be estimated solely with reference to its effects on the management of cancer: the fallout is considerable. For ex¬ ample, the transplantation of tissues and organs was made possi¬ ble by the judicious use of immunosuppressive drugs secured by raids on the storehouse of chemotherapeutic agents devised for use in the treatment of cancer (among them azathioprinc,

Imuran, and methotrexate), Epidemiology' has also thrown important Light on the relation¬ ship between sex, reproductive history, and cancer. For almost all cancers married women are less at risk than single women and women generally have lower cancer rates than men. In women. moreover, there arc clear correlations between cancer risk and re¬ productive history. Cancer of female reproductive organs is more common in childless women than in women who have had chil¬ dren and its frequency falls as parity (number of children born) increases. In both North America and t he countries of northern Europe, ovarian cancer reached a peak in the generation of women born in the quinquennium 189.V ll>00, in which fertility was so low that demographers of the thirties wondered whether people of the Western world might not die out, There is also a most interesting correlation between age of a mother at birth of her first child and risk of contracting breast cancer: teenage moth¬ ers have less risk than mothers who were twenty-five or more when their first child was horn; and women pri mi parous at thirty or older have a decidedly' higher risk of breast cancer than child¬ less women.

49

CAROTID ARTERY

CAROTID

ARTERY

Thin is the major blood vessel in the neck that must surely be intended when inexpert thriller-writers refer to the j uvular.” The internal and external carotids are tile principal vessels trans¬ porting oxygenated blood from tlie heart it> Lite head; it is occlu¬ sion oi the carotid dial causes rapid loss of consciousness, and the carotid whose inadvertent puncture by a surgeon is sure

ECt;

use of an argum view die sequence fmni the wrong end: the proper starting point was the germ and the real question w-as “How are the Characters of an organism represented in the germ cell that produces it I*” or, as Samuel Under has ii, (he propei' sia.temetu of relation between successive generations is . . . “to say that 4 a hen is merely an eggs way of making another egg.’ “

(p. 1B7)

Darbyshire’s attribution of the epigram to butler is unequivo¬ cal, although Butler himself in a footnote to the second edition of Life and Habit (London, 107® merely commented, “It lias, 1 be¬ lieve, often been remarked that La hen is only an egg’s way of milking another cgg.f” There is not much pride of ownership 53

CHIMERA

here, hut wc believe that the reason for the Form it lakes is dial Samuel Butler wan too modest to say, as he plight reasonably have done, “As l myself have so aptly and windy observed, lA hen is etc. . . ” We must court! it a mercy (hat (he remark came too late to be attributed to Oscar Wilde. Puller's epigram , which embod¬ ies one of i lie most profound truths of biology affirming as it docs the primary importance of the replication of DNA was un¬ familiar to the late Jacques Monod, and we were fortunate enough to witness his delight upon first hearing it. Hen and egg feature also in a famous riddle that is often thought to embody an un resolvable parades: “Which came first, the chicken or the egg?1' The two possible answers neatly define two entirely different biological and political philosophies. A per¬ son who [relieves that the egg came first [flat a new kind of egg must have conic before a new kind of Chicken is a Mcndelist and a M organist, and in (lie Western Hemisphere a I rust worthy and regular guy (some compensation, perhaps, for the odium of being classified in the Soviet Union as a genetic elitist and a running dog of fascism intent upon still further subjugation of the Working class). Conversely, someone Who believes that the thicken tame til's! that a new kind of chicken, wiser or prettier, perhaps, than its pare n is, can produce a new kind of egg would a< one; time in the Weslem Hemisphere have been denounced as a secret agent of i he Comintern working to overthrow the constitution of the United States. There are of course many other epi grams and tropes making use of the imagery of chicken and egg, though nn oilier goes as deep as the two we hast chosen: we stop short, for c sample, nf com ending that Don't count your chickens before they’re hatched" embodies some subtle demographic consciousness of the prevalence of infertility.

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11

CHIMERA Like mu tli else in classical mythology, the chimera tries one’s patience as sorely as :i fries one’s credulity. Tin: classical chimera, the progeny oT Tvphon and F.ehidna, monsters both (evidently she condition ran in the family), was composed of three parts a she-goal in the middle, with a lion before and a serpent behind! 54

CHORDATA

In biological science, a chimera Is an animaj compounded gf cells of two or more dilfercni genetic provenances. Il is different

from a Hiftfflf'c, although a mosaic is also an animal containing cells of different genetic makeups- in a mosaic the genetic differences between the somatic cells have arisen by abnormalities of cell di¬ vision affecting the chromosomes, especially m the early stages of development (tints sortie insects, gynandrorrtorphs, arc male on one side of the body and female on the other); or, alternatively. mutations may have appeared in one or another of the cclh division lineages (hat give rise to the adult body. Natural chimertsni occurs regularly in fraternal twins in cattle, rarely in human beings. Twins of this sort often share a placenta and can thus commingle their bloods and blood-forming cells during fetal life. Such chimeras accept grafts from each other without rejec-j tion and thereby appear to flout the rules of transplantation but tli is is true only because they become mutually tolerant of each other’s tissues, Twin chickens (two chicks hatching from one egg) may be cither identical or fraternal; the latter are always chimeras. .Artificial chimeras can be manufactured by a laboratory re¬ production of the phenomenon, that occurs naturally in synchorial twins and can also be raised by fusing two very young em¬ bryos to form ii single organism that has come to be described as "tctraparentald’ Another circumstance in which chimeras arise is when for any reason (for example, because uf x- irradiation or gamma-irradiation) blood-forming cells have been destroyed and are replaced by an inoculum of blood-forming cells to make a ge¬ netically different animal. These are radiation chimeras. Chi¬ meras comprised of elements as disparate as the classical chimera remain purely fictional beings: experimentalists do not try to pro¬ duce them because such an enterprise would be uninformative

—

and

pointless,

CHORDATA

Chordata is the taxon that includes all vertebrate animal? and many lesser groups related to vertebrates by evolutionary ances¬ try. Chordatcs are animals which at some stage of their life [rossess a Miioi-hurd, a tough but flexible skeletal rod running along the 55

CHROMOSOMES dorsal length tiF the body. Until the evolution ol paired limbs (something of an innovai ion), churdates typically moved by means of sigmoid snake- 1 ike contractions passing down the trunk, which straightens out by the elastic recovery' of the notochord. Fn chorda tes the central nervous system is characteristically a hollow tube formed by the rising up of two as it were "shoul¬ ders” of the cells that constitute the outermost layer of the embryo, forming first a Longitudinal dorsal gutter or deep groove arid then, by a closure across the mid Line, a lube open¬ ing posteriorly. The heart is a ventral structure, and the principal body cavity, the coelom, is formed hy the enlargement of a cleft that forms in the "mesoderm” between the outer ectoderm and the embryonic gut. It is characteristic of vertebrates that die anterior stretch of the gut (the pharynx) is perforated by clefts (gill slits) which serve a respiratory function, and that the sortiatic musculature originates in the form of segmental blocks lying on either side of the notochord and running from end to end

of the body. 'The closest living representatives of the primitive chordales that were probably ancestral to verlcb rales arc the thirty-odd species of lancelct that make up (he gen ns Bitincfna\lt)nm (= arnphiuxus), and this form in turn is very closely related by develop¬ ment to i he animals known as 7 unicata (sea squirts), the larvae of which have a notochord and a median dorsal nerve tube. Other animals too satisfy some of the enter in ol ihe phylum Chordata, fur example acorn worms and arrow worms, the word "worm” being improperly used in both contexts.

CHROMOSOMES Ch romosomes are the vectors of genetic information in all ex¬ cept the very simplest of the organisms, which are known accord¬ ingly as prokaryotes. Self- rep reducing bodies of the nanometer order of size (one nanometer equals one billionth of a meter), chromosomes are housed within the nuclei of cells, They vary greatly in ap[>caraiice, and their conventional characterization as threadlike does not describe them adequately; some are rather stubby and prickly, Like caterpillars, and others more ribbonlikc,

5(j

GMROMOSC >MKS

as noodles are when compared with spaghetti. The complete con¬ fidence with which one can declare chromosomes (he Vectors pf genetic information is built upon a variety of sources nf evidence, ol which the first and most in i port ant is the extremely exact cor¬ relation between (he 'observed behavior of chromosomes and the postulated behavior of Mendel’s "hereditary factors"; thus chro¬ mosomes are present in pairs, one member of cacti pair having been derived from one parent. In gamete formation chromosomes segregate, only one chromosome of each pair entering each ga¬ mete. Gametes accordingly end up with only half the parental number of chromosomes with (he haploid, as opposed to the normal diploid., number. The reproduction oT chromosomes is the primordial act of rep¬ lication in biology; a chromosome is not synthesized de novo but is asset nbled as a copy of a preexist ing chromosome: in othci words, a chromosome forms only when there was one before. The same is true of many other cellular constituents such as mito¬ chondria and chloroplasts. ail described as self-reproducing; Sec

—

our entry on NUCLLf£&&ciD£. In the u jit on of gametes at fertilization die chromosomes pair off again and tin: diploid number is restored. When linkage (dial is, inheritance of Meriijdian factors not singly but cn bloc) came to be known as a genetic phenomenon, it was satisfying to learn that the number of linkage groups was equal to the number of pairs of chromosomes, so that the chromosome could be regarded as a physical embodiment of the linkage group, Thomas Hunt Morgan (1866-1945), renowned American embryologist and ge¬ neticist, was the first to demonstrate that chromosomes are dif¬ ferentiated along their length. High- resolution microscopy even¬ tually' made it possible to identify various structural singularities along the length of the chromosome and often to correlate ilsest: with specific genetic effects; genes as such were not visible, how¬ ever, being merely local combinational singularities of the nu¬ cleotides of nucleic acid, In spite of the extremely powerful circumstantial evidence of ihc complicity of chromosomes in the hereditary process, sonic ge¬ neticists were unconvinced, or professed to be so. One of these was the English geneticist William Bateson, who in his great text Mtndfl’s Principles oj Heredity (Cambridge, 19011) did so much to

57

CHROMOSOMES

make Mendclism known to the English-speaking world, It may be that Bateson was anxious for it to be more widely realized that the existence of chromosomes and of what later came to be called genes could be inferred from genetic evidence without recourse to die microscope. Bateson and others of like mind found many rea¬ sons for questioning the complacent assumption that chromo¬ somes were the vehicles of Mcndelian factors, Chromosomes are visible in the dividing cell, but as a rule not in the resting cell be¬ tween divisions. It was at one time thought formally proper to express some misgivings about this apparent interruption, but the concern was wholly simulated; for in the light of genetic evidence positively requiring chromosomal continuity, no geneticist had any real misgivings. It is now known that some chromosomes can be seen in the resting nucleus (notably and most usefully the extra X chromosome of females named the Barr body alter its dis¬ coverer, Murray Barr). Chromosomes are composed of deoxyribomiclcoprolein a salt-like compound between nucleic acid and a basic protein such as histone, the genetic function of which is not known, although the teleology of chromosomal organization is obvious enough. The chromosomes form a system of packaging nucleic acid in such a way as to prevent a variety of accidents which if they oc¬ curred would make nonsense of the essentially conservative pro¬ cess of Men del i a it heredity and the orderly process of develop¬ ment (accidents such as the casual leakage of DNA into or out of nuclei, or the cross-infection of the nucleic acids of neighboring chromosomes)- The chromosomes themselves do undergo acci¬ dents that have recognizable and sometimes very' deleterious ge¬ netic effects; among them are multiplication of chromosome num¬ bers above tlte normal or cuploid condition. This is known as polyploidy, which sometimes takes the form of’ the presence in triplicate of a chromosome that ought to be present only in dupli¬ cate, as with the human chromosome J2I in Down’s syndrome. Chromosomes also have a role in SEX DETERMINATION, which is elaborated in the genetic definitions. Because physicists have played such an important part in the study of nucleic acids, it is worth remembering that it was a phys¬ icist, Erwin Schriidinger (1887-1961), who in What is Life? (Cam¬ bridge, 1944) first described the chromosome as the physical cm-

—

—

5tt

Cl JONES

bud i mem ol" a code-script for heredity. The image became very familiar when the special relevance of information theory to bioh ogy came to be appreciated.

CLONES

A clone of cells comprises the progeny oT a single parental cell, as a tumor is now thought to be, by repealed and successive mhotic (genetically symmetrical) cell divisions. Thus in a sense an adult organism is a clone descended from the zygote, The word “clone" may also refer to progeny of whole organisms that repro¬ duce asexually. The connotation is that of identical replication. Thus identical twins that have been formed by tile division into twro equal parts of a fertilized egg constitute a first -order clone; indeed, the eggs of mammals arc of the kind that lend themselves in principle to cloning, that is, to the production of a large if not indefinite number of replicates of a prototype. The practical reali¬ zation of such a foolhardy ambition would call [or the prolifera¬ tion of a fertilized human egg under tissue culture conditions and the provision of an adequate supply of young foster mothers hor¬ monally prepared for implantation of the egg. None of this is technically very difficult to accomplish: what is required all in One place is the ambition to accomplish it, a sufficient concentration of money, a modest technical proficiency, and folly, In science fiction, however, and to some extent in popular speech, cloning has acquired an extra connotation: the replication of a fertilized egg which has been caused in acquire a genotype of choice by replacement of the zygote’s own nucleus with the nu¬ cleus of a body cell of the person a mad or vain millionaire, say of whom replicates arc to be made. An unscrupu lous science journalist wrote a professedly documentary book on just such a theme, pretending it to be a true life story but at the same time declaring himself so bound by oaths of secrecy that there was no possibility of verifying the tale (or the probity of its author). The book was accompanied by a quasi-scientific appendix, and that was also a skillful exercise in the concealment of tracks. The au¬ thorities quoted were said to have been consulted pseudonynmusly bv the author. Many people were taken in by this yarn,

—

—

59

COM ii.\ RATI V H: A NATO M V

which wfe consider highly discreditable to author and publisher alike. In our carefully donsidered opinion, clomfitg with this extra Connotation of choice of genotype is not feasible in human beings. Cloning of plaids is the phenomenon to which the word h-setf was firs I applied, with reference to the well- known propagation of plants bv cuttings, runners, budding, or grafting: the term has now beetl exl ended to the raising oT whole plants (for instance, whole carrot plants) from single cells, "fhis usage resembles the nihers to which we have referred, in maintaining the essential connotation of asexual production of genetically identical repli¬ cates.

COM PARATI VE AN ATt >M Y hi the great post -Darwinian era, when ihe principal business of biology was a demonstration of evolutionary descent ever more cogent and ever more specific, comparative anatomy was biol¬ ogy's central discipline. Jf carried out convincingly, comparative anatomy is an exact and an exacting pursuit that calls for the ex¬ ercise of nice judgment and a certain amount of Hair. Considered pedagogical] y, com pa ml! vc anatomy has many of the viiiucs tra¬ ditionally associated with Lhe classical education called for by the hu inanities: it is understandable that in many eminent schools of biology it has remained the core of the teaching syllabus, one ol list: most famous of such schools- being the department of zoology and comparative anatomy at Oxford University. Among its graduates have been one of the world’s leading geneticists, a dircoteir nf ( he London School of Economics, and a former director-general of UNESCO— -so evidently the study ol’ com¬ parative anatomy docs not unduly narrow the: mind. The au¬ thor* of this booh write with a degree of pride excusable in alumni.

Among the triumphs of comparative anatomy is a sinking ex¬ ample of (he concept of homology. Comparative anatomists were the first to demonstrate that the miscellaneous animals formerly lumped together as 'ungulates” walk on the tips ol their iocs hence the name. The Knee oT the horse corresponds anatomically to the wrist or ankle; the horse walks upon the single digit, cor re¬

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1

lit)

CORONARY ARTitl-tV

iponding to our middle finder or middle toe. tUi>i 2 and 4 being reduced to “splint bones." The so-called even-toed jtpgulates such as sheep and cows walk on dibits 3 and 4, with 1 and f> being ves¬ tigial and sometimes disappearing, Another interesting and unexpected finding |jj Comparative anatomy was. that the tiny bones of the car dial transmit vibra¬ tions from the eardrum to the organ of hearing were formed front the hours oi the jaw liberated when the toWfer jaw of mam¬ mals was reduced to a single bone, the deniary. Again, the muscles that move (he eyeball derive in evolution and develop¬ ment from the three most anterior muscle blocks of the series that ai one time occupied the vertebrate body from end to endin this sort of way, comparative anatomy has made evolutionary sense of ihe varieties of structure found among vertebrate ani¬ mals.

CONTACT INHIBITION

The discovery by Michael Ahercrombic (I 912- 1979) of a sim¬ ple regulatory phenomenon, the mutual deterrence of amoeboid movements when cultivated cells come ill contact with one an¬ other, explained much that had until then been mysterious (for example, the fad that the repair of artificial wounds indicted on tissue culture proceeded only just far enough to make good the loss). Special interest was natural ly aroused by Abercrombie's demonstration that contact inhibition is dclectrvc in malignant cells, a property that goes some way to account for the invasivcncss of tumors. Future invest igat tun of eonlael inhibit inti is likely to turn on defining, probably by immunologic methods, the struc¬ tural properties of cell surfaces that conduce to e'otuact inhibi¬ tion or under pathological conditions to its failure,

ARTERY' The coronary is the great artery wrapped around tho heart that provides the continuous and abundant supply of arterial blood demanded by the musculature of Lhe heart (the myocardium). It is in a sense tile most important artery m the body, because upon

CORONARY

til

CREATIONISM

its correct functioning depends the functioning of all the others. Perhaps because of the continuous pounding and jolting it is ex¬ posed to, the coronary artery is rather particularly susceptible to the pathological changes to which arteries in general are vulner¬ able. Coronary' arterial disease is frequently a precursor of coro¬ nary heart disease, which in extreme form may lead to complete occlusion, often followed by death of the heart muscle (myocar¬ dial infarction). In the industrial Western world cardiovascular diseases have for some time been edging their way to the top of the list of causes of mortality'.

CREATIONISM

Scientists other than biologists have noted with surprise, per¬ haps with annoyance, the bland self-assurance with which biolo¬ gists have usurped the entire reference of the term “creationism,” II is not surprising that they should have done so, because the bio¬ logical is that aspect of creation upon which scientific evidence is most completely at variance with the biblical narrative and the only aspect of it which had been the subject of a case at law. We refer to the notorious trial in Tennessee of a schoolteacher, John T. Scopes, for violating state law by teaching the theory of evolu¬ tion, This trial is within the authors’ memory, but is remembered by most others as the subject of a thrilling forensic confrontation between Spencer Tracy and Fredric March. For biologists, then, creationism connotes the teaching that the Lord created every single species of animal and plant found in the world today, whereas biological orthodoxy has it that existing species arose over hundreds of millions of years as a result of the differentiation and divergence of their several biogenetic lin¬ eages a hypothesis compatible with all the empirical evidence. The special creation of living organisms is pan of the story, of course, but not the whole of it: what about those first verses of Genesis that answer the question “How did everything begin?” Surely creationism must comprehend the answer. The same goes for the origin of life, a subject upon which Darwin felt that specu¬ lation was useless, We are surprised at the obstinacy' with which creationists

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62

CURARK

id literal creationism. So doings they fail to realize that the evolutionary concept is a much grander and more awe-inspiring conception -in keeping with what C. S. Lewis referred to as rapiety, and fijttf many people conducive to rtvcrnicc. It is a pity that we still live under the dark influence of the single-

handed inauguration by bishop Samuel WiJberfcrce (“Soapy Sam") of an essentia! tension between biological science and (feligion.

Another consideration is that creationism in the biological sense and especially such glosses upon it as Archbishop Ussher’s (l5flUlfi56) calculation that treat ion took place in 400$ it.r:. can be empirically faulted as myth; Norse mythology, for exam¬ ple, has it that ihe sun is pursued across the sky hy two ravening wolves, bkdll and Hati, who cause partial or total eclipses of the sun by biting off part or swallowing it whole. The first few verses of Genesis cannot be empirically falsified and should perhaps her classified as imaginative literature rather than as myth. Furcly sc ion ii fie evidence has not much bearing on its acceptance: wo cannot conceive of a frontier without conceiving that which lies on either side of if; how then can we conceive in scientilie forms the frontier bci ween being and nothingness, having in mind that nothingness can have no sensory content and can tint therefore be the subject of empirically based judgments':* These are matters of faith: they lie outside science, and the popular idea that scientific evidence has refuted the biblical account of the primordial crea¬ tion is not philosophically tenable.

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CURARE Curare is an arrow poison extracted by Stmt Is American In¬ dia ns from she root bark of certain poisonous plants, especially Sttychnos io-xifera. When introduced into the body parent orally (otherwise (ban by mouth), it blocks the connection between motor nerve and muscle, hirst to be paralyzed are the muscles moving l he eyeball, then (it her vohnuary muse Its, and finally the muscles of the diaphragm; death subsequently occurs through re¬ spiratory failure. Curare has abundant uses in surgery as a muscle relaxant. Neostigmine (an am icholinest erase) is kept at hand for use in G3

CYBERNETICS

of poisoning by curare arc in some those of myasthenia gravis.

emergency. The ways similar to

symptoms

CYBERNETICS

This especially apt neologism was coined by Norbert Wiener (CyfifTTiriics [New York, IfMfi)) From the Greek word gubermles (meaning ‘‘steersman”) and intended by Wiener to refer to ‘‘the entire held of control and communication theory, whether in the machine or in the animal.'’ In introducing this notion, Wiener makes special reference to a paper by James Cleric Maxwell pubhshed in (he Proceedings uf the Ruyut Society of i/md&H in I HEitj, Writ¬ ing of governors, Maxwell gave an elementary mathematical treatment of positive and negative feedback and called attention to the inherent instability of the former. In the exercise of control, the stratagem r>f feedback plays a par¬ ticularly import a nt part, for feedback is the control of perfor¬ mance by the consequence.!; of the act performed. Of universal occurrence in biology, feedback is described as. negative when the retroaction of output upon performance is to diminish it. An ex¬ ample in point would be [he lowering of body temperature by the sweating that follows an elevation of body temperature. On the other hand, positive feedback is illustrated by the slate of af¬ fairs that arises in certain ‘‘autoimmune*’ or iinmtmologieally self-destructive diseases, in which one cT the first clients of the dis¬ ease is to create anew and therefore i*em force the very conditions that led lu the disease in the first place. An injury to the thyroid gland which gives rise to autoimmune thyroiditis (in effect, !o an¬ tithyroid antibodies reacting upon the thyroid) leads to ihe for¬ mal inrt of an i i bodies that generate still further damage to the thy¬ roid and therefore acerbate the disease. We have previously used a familiar everyday example to illus¬ trate the principle of positive feedback: ai a noisy cocktail party people have to speak louder and louder to make themselves heard. This adds to the prevailing din and so makes hearing even more difficult, causing everyone to speak louder still, Positive feedback creates an essentially unstable situation, leading in extreme eases to violent oscillations and even breakdown of the system. G4

CYRKRNETiCS

It would not be feasible to enumerate all ike situations irt which t he stratagem of feedback is used in the regulation of bod¬ ily performance, for feedback is ubiquitous. To give one example, in the endocrine system release of the: hormones produced by the thyroid gland, the adrenal cortex, and the reproductive organs is stimulated by so-called trophic hormones produced by the pitui¬ tary gland. Production of these trophic hormones is switched off by the hormones whose liberation they stimulate, and thus the output of a hormone is maintained within physiological limits by the hormone itself, As with information theory, the terminology and concepts of cybernetics were quickly taken up by biologists and have, so to speak, passed into the language a sure sign that they were needed.

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65

DEFINITION

OF LIFE AND OTHF.R TERMS

In certain formal contexts- mathematical logic, for example, in which a definition is a rule for substituting one symbol for one or more others —definitions are crucially important, but in every¬ day life and in sciences such as biology their importance is highly exaggerated. It is simply not true (hat no discourse is possible un¬ less all technical terms are precisely defined; if that were so, there would be no biology'. A principal purpose of definition is to bring peace of mind. Sometimes, though, it is too dearly bought: a "definition,” as (he word itself connotes, has a quality of finality that is often unjusti¬ fied and misleading and may have the effect of confining the mind instead of liberating it. A great many nnnhiolngists believe that animated and contentious discussions of the definition or "life” are a principal preoccupation of institutes and university departments of biology. In reality, the subject is not mentioned at all, except perhaps to disparage the rather simple-minded people who believe that an agreed-upon definition of life will lead LO a better comprehension of biology. Biologists already have a work¬ ing understanding of “life” that is good enough for present pur¬ poses; we do not believe that any current research enterprise is at all impeded by the tack of a more formal definition. The trouble is that "life,” like many other technical terms m science, has been pirated from the vernacular and is used in scientific contexts far removed from those that might arise in common speech. Situations do certainly arise in real life in which a definition of "life” (or anyhow an exact description of all that "living” con¬ notes) is genuinely important. Consider, for instance, the decision whether or not to use ibr grafting the kidney or other organ of a potential donor whose heart may still he beating. Such a decision turns upon a number of technical evaluations that belong to a world far removed from the entries in a sematological dictionary; 66

I)KMO(;RAKHY

the assessment of brain function especially, and the truest ion of whether the condition of the possible donor js reversible or not. These arc factual, empirical questions that reference to a dictio¬ nary will not help to answer. A hunger for definitions is scry often a manifestation of a deep-seated belief -one of the many philosophical fancies made fun nf in Lewis Carroll’s enchanting rVt Wonderland anti Through the Looking Glass that all words have an inner meaning that patient reflection and research will make dear and distin¬ guish from false or counterfeit meanings, which may have usurped the true meanings; indeed, amateurs will sometimes put a question about; definition in a form which reveals their enslave¬ ment to this illusion: I! What isrhc/rii/ meaning of the word 'life’?” they ask. There is no true meaning. There is a usage that serves the purposes bf working biologists well enough, and it is not the sub¬ ject of altercation or dispute.

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DEMOGRAPHY

The branch of learning that has to do With the growth, repro¬ and vital statisi its of populations was first thrust into the forefront of public attention during the l-930s. Widespread feats that the people of the Western world were dying out through in¬ fertility before long were .supplanted by the view that advances in medicine combined with the high fertility of the developing na¬ tions threatened an explosive increase in pop ti lit lion, as disastrous in its way as decline through Infertility. duction,

In demography, as in developmental biology, a certain fastidi¬ ousness Is called for in the use of technical terms. Every teacher who has heard students define “death rate" as “the number of people who die per thousand3’ would agree. We therefore include below a few definitions of frequently misused words and phrases. DEATH RATE Tim notion of a death rate in demography sounds straightforward enough, but in using the notion one must have in Hie forefront of one’s mind the nature of the independent variable in rela¬ tion to which the rate is expressed. According to the uses tq which it is to be put or the inferences that are to be drawn from it. a death rate may

67

DEMOGRAPHY he expressed as the number of persons per thousand who die in a calendar year [for example, ] HU 41 or in a year of age (in the seventieth year, for instance). Each has its special uses; in some ways the most in forma¬ mte the number who die in any year tive measure is t hÿ:*ÿ-ifrtcific of age (bet wet; n the years x and .t + 1) expressed as a fraction of those still alive at age x. The age-specific death rate is often referred leas the force of mortality.

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LIFE EXPECTANCY The registration of births and deaths that is commonplace in all civilised countries puts It within the power of a gov¬ ernment1:! statistical office to estimate a person's average ex.|>eciatiorL of further life at birth qr at any other chosen age. hi principle, the calcula¬ tion is quilt straightforward: it involves estimating from the data the total n timber of person-years lived by people of any chosen age and di¬ viding the product by the number of fxLrsons to live them. The mean expectation of life at birth, often used as a measure of the well-being and general medical prowess of a population, has increased dramai ically over die past few hundred years. This is true mainly be¬ cause of the diminution of mortality in infancy and childhood (itself the consequence of the improvements in medicine and in sanitary engi¬ neering that have reduced deaths from infection to a very low level).

The

ittean

expectation of life

at

later ages has not increased nearly so

much. Older jxÿople nevertheless have a lot going for them, not the least being the heightened resistance conferred by previous sublet hal expo¬ sures tip infectious agents a sort of immunologic wisdom and in addi¬ tion by wisdom of a more conventional kind (embodied in the phrase “once bitten, twice shy”).

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Mean expectation of life (hi years) in at

Period

Sex

birth

Age 60

1755-1*76

Malt he male

35.20 55.70

12.24 15.0b

Mule Female

40-48 44.15

18.12 M.1H

4,91

195b- 1940

Made Female

64.30 66.90

111.35 17.19

.5.25 5.49

1971-1975

Male Female

72,07

17.85

77.05

21.29

6.08 7.2fi

]856ij860

68

Age Stl 4.27 4,47

3.12

DEMOGRAPHY

—

The mean expectation olfifc of females is at all ages including per¬ haps imm conception LLJYI i I: birth- greater lhan that of malt:s. The most complete records wc have arc from Sweden. The accom pa [tying table, which applies without difference of principle to North America and Great Britain, is seen te> illustrate all die points that have been made above. M ALTH USlA N PA RAM ETER Ronald A. I’islicr's term for Alfred I.otkab ''true rate of natural increase” is an attempt to represent bv a

J.

single figure the reproductive vitality of tt population. Where is the birthrate and /, the likelihood ofliyiri g to age A;, tlie Malthusian parameter w is given by solution r:f iluj equation

J

eÿi&ttx-l.

0

The Malthusian parameter w as thought by l,olka to be an improvement on the earlier net reproduction ratio (see next definition), bm its use is Open to the same objections. NET REPRODUCTION RATIO Robert Kuczynski made I he first and most famous attempt to solve an imritisienlly insoluble demographic problem: to express the reproductive well- being and the future growth prospects of a population by a single arithmetic figure the ne1 repree duct ion ratio, or XRR. (This is somewhat analogous to reading a pa¬ tient's temperature on a clinical thermometer, as if it were possible to lake the nation1* temperature in the same sort of way.) The :N’RR may be viewed as an answer to die question, What i* the likelihood lhat a specific individual today will lx1 represented by a person of the same age in i he next generation? If we confine our attention to female births only, i fie NRR may be expressed as the ratio of live female bin hs in successive general ions: if 1 lie value is unity, the population may be thought to be just holding iis own; if less lhan Unity, the population is rc productively losing ground; conversely, tl'ilie value is more than unity, it is increasing in number. Modern demographers do not accept the principle of mea¬ suring a nation* reproductive health in this way. The single- number

—

valuation of complex quantities (*ee I1. R, Medawar, f‘In/vrs Republic [Oxford, 1982], pp. ffi“-l'M) is doomed to failure in tfii*, as in many other contexts.

fi9

DESIGN, ARGUMENT FROM

DESIGN, ARGUMENT FROM The argument takes two forms, of which Lite more familiar might be described as the case from design for the existence of God. The argument is that Nature everywhere manifests a functional fitness and working capability that is evidence of design as dear as can be seen in a watch or engine or other such artifact. Design implies a designer, William Pa Icy (1743 1805) reasoned; was this then not die supreme being, God? (“Why only one?” Hume had asked in his own skeptical reflections ori the argument from de¬

sign) The other form of ihe argument from design professes to infer only the existence hut also the benevolence of God. One does nut have to be a card-carrying monadoiogisl such as Leibniz (1646-1716) to conceive that ihe world might have taken a form other than the one in which we find ii, hut it would be downright impious to suppose that God, if He created the world, would cre¬ ate anything other than the best possible world. It is well known that Voltaire’s Candidt vigorously dissented from this view. Al¬ though in many ways a dull and tiresome book, it is, like so many satires, better known than the idea it satirizes that Lhis is the best of all possible worlds. This second form of the argument is more ambitious: it pur¬ ports to infer from the evidence of design not merely the existence of God, hut some of His character traits also, especially His good¬ ness. To demonstrate this was the a mb it ion rtf the Right Honour¬ able and Reverend Francis Henry Egcrton, Earl of Bridgewater, who died in I8tlf) and directed in his will that the (at ihat time) munificent sum of .£8,000 should be invested in gilt-edged securi¬ ties so that the dividends therefrom might Fund the publication of one thousand copies each of eight treatises “on the Fower, Wis¬ dom, and Goodness of God, as manifested in the Creation; illus¬ trating such work by all reasonable arguments, as for instance the variety arid formation of God’s creatures in the animal, vegetable, and mineral kingdoms; the effect of digestion, and thereby of conversion; the construction of the hand of man, and an infinite variety of other arguments; as also by discoveries ancient and modern, in arts, sciences, and the whole extent of literature,” With the piety expected of indeed statutorily required in not

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id

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DOWN’S SYNDROME the head of an Oxbridge college, William W'hewelJ in his own Bridgewater treatise wondered whether "the whole mass of the earth from pole to pole and from circumference to centre" might not be "employed in keeping a snowdrop in fhe position most suited to the promotion of its Vegetable health/* This quotation. which wo learned from Jonathan Howard's admirable Darwin (Oxford, 1982), epitomizes the spirit of ihe Bridgewater t rea¬ lises documents a modern Hume would make short work of, Another gem like WheweiFs was exhumed by Sir George Porter (see Ids "Sir Humphrey Davy Poet,” Interdisciplinary Seimee Re¬ views 3 jl97H|;2fj2) from Davy’s notebooks at ihe Royal Institu¬

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—

tion;

The eternal laws

Preserve one glorious wi$* design; Order amidst confusion flows, And all die system is divine,

In reality one can learn no more about the benevolence of God from ihe evidence of Nature titan one could learn of (he solvencv of a company that presented its shareholders with a balance sheet containing Credit entries only, And this is the philosophical gim¬ mick of the Bridgewater treatises; Nature’s success stories arc lin¬ gered Oyer and recounted, but the errors of nature, its many mab adap tat ions, and the cost of fitness in blood, pain, and mortality are left unpriced. It is no wonder that God cuts such a good figure in the Bridgewater treatises.

DOWN’S SYNDROME This is the medically approved name for the congenital afflic¬ tion vulgarly known as mongolism, originally so called because of John L, H, Down’s belief that It rcprescnied an example of ata¬ vism, an interpretation abetted by the supposed resemblance to the Mongolian facies of the broad, rather flat face and slanting eyes of some afflicted children. Although the mental retardation and general incapability that accompany Down’s syndrome are its most distressing symptoms, the disease is marked by many other abnormalities of the internal organs combined with a gen-

71

DOWN’S SYNDROME

shoots

era] vulnerability to infections arid the of life. Although to some degree edticiibLe, children with Down's syndrome do not often become independent of special can: and their life expec¬ tancy is lower than that of normal children. The frequency of Down's syndrome in the general population, more than l per 1,000 live births, rises very steeply with the age of the mother. Obstetricians, therefore, now recommend amniocen¬ tesis for pregnant women over thirty and, a fortiori, for expectant mothers in their early forties, in wlto tn the frequency of Down’s syn drome may lie more than l percent of live births. Dflwti's syndrome is a consequence ol a gross abnormality oi the chromosomes. Two classes of abnormality are especially asso¬ ciated with the affliction. One is trisomy-?I (the presence in tripli¬ cate of a chnuno&oiiie, number 21, that should be present only in the usual double form). Thu other abnormality is that in which chromosome 21 is present in excess because of the translocation to it of material from another chromosome, ft is the trisomic form of Down's syndrome that Increases in frequency with maternal age; Down's syndrome resulting from tra ns local ion is not so sLrotigly influenced by maternal age, but unlike the other form may run in families. Chromosomal abnormalities cannot be corrected, I he tix'almcnl of Down’s syndrome is confined to general care and sup¬ portive treatment, which in a humane society will extend to the parents ef the afflicted child as well as to the proximate victim.

It

EcotbcVi Tlje words “ecology, ” "economics,” and '‘ecumenism" all have their root in the Greek word otkas, meaning house or home. Ecol¬ ogy, topmost in the hierarchy of the life sciences, has Indeed to do with the economy oT the great house of nature, of which it seeks to reveal the si rue lure in space and time and especially the interar-

tiona of animals and plants vs- 1 1n themselves anti with each other, Its content is enormous, for ecology enjoys the entire empirical content of the sciences belpyif it irt the hierarchy as well as, of course, the concepts contextual tv peculiar to itself. The hierarchical ordering of the biosphere is discussed in the entries FiiEtRAKCri TV Find RFOUCTrONISM, Just as characteristic is the cyclic ordering of the biosphere: cycles pervade the whole of animate nature. First, of course, we think of the slow pulse of the seasons upon which are superimposed l In: lesser cycles of the months -tile tides and the alternation of night and day. The whole pattern is of cycles within cycles within cycles, the least of all that with the fastest pulse rate being the cell-division cycle in growth, in the continuing process of cell replacement and tissue repair, and in some physiological processes such as antibody formalion. The [Movements oT [he elementary' constituents of ihc bio¬ sphere from organism to and from cn v iron men t, and from orga¬ nism to organism, arc also cyclic in nature. Carbon, oxygen, and nitrogen arc never stationary, buL are at all times on the move in the biosphere. Thus m the lood chant compounds of nitrogen pass from orga¬ nism to organism. Find nitrogen is eventually ret Timed 10 the soil or to the atmosphere by the putrefaction of living organisms and their excrement brought about by the bacteria Lhai deni¬ trify nitrogenous compounds and ret urn molecular nitrogen to Lhe atmosphere. Nitrogen is recaptured by microorganisms in the roots Of leguminous plants t lint can use atmospheric nitrogen, and

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73

ECOLOGY

also by industrial processes on an enormous stale that convert at¬ mospheric nitrogen into ammonia and nitrates which reenter liv¬ ing organisms through their use as fertilizers. These various events constitute the “nitrogen cycle," of Immense importance because the cyclic movement of nitrogen is the limiting factor in what may be thought of as the “metabolism" of the biosphere (if we use that word in a sense not remotely different from its use in refer¬ ence to individual organisms). Oxygen and carbon cycles, are closely related and intersect in the process of photosynthesis, in which the energy of sunlight transforms water plus atmospheric carbon dioxide into carbohydrates, accompanied by the libera¬ tion of molecular oxygen, which is used in the respiration of both animals and plants, Analysis of the cycles of the elements and preparation of bal¬ ance sheets relating to them is a principal task of ecology. It is here that we naturally turn for guidance on such world problems as the conservation of water and the dangers entailed by the in¬ crease of carbon dioxide in the atmosphere resulting from the huge scale of industrial processes involving combustion and therefore consumption of oxygen. More carbon has been locked up in the form of coal and other fossil fuels than in the living or¬ ganisms of the biosphere. Plants, of course, make use of atmo¬ spheric carbon dioxide, and again it is to ecology (bat we look in attempting Lo assess and remedy the consequences of the destruc¬ tion of forest lands. From the standpoint of die metabolism of the biosphere the participation of the sea, and especially of the mi¬ nute marine plants of surface waters (the phytoplankton), are quantitatively of the highest importance. Thus ecology, meteorology, and geophysics have many com¬ mon interests. Modern ecology has moved a long way from the days when a biologist with a vasculum, lens, butterfly net, and supply of sandwiches rated himself an ecologist if he recorded the varieties and the degree of abundance of living things in a fresh¬ water pond, a rock pool, a copse, or an area of arable land. Every¬ thing is now very sophisticated and depends upon the use of tech¬ niques no longer within reach of the amateur. Moving animals may be made to declare their presence by minute radio transmit¬ ters that betray their positions: worldwide schemes of marking and recapture uncover major migrations of animals and 74

KM1SRVOM1C AXIS

invaluable aids in the extraordinarily dillicult msk of eompillug l.iftL tables Fur living organisms in :i natural environment, The concept "natural" is crucEgjJ, For ecology lias in common with ethology a strong convict ion that its principal business is with the Manual world —with the world as it is, Father than wiih ex¬ perimental simulations ol'ii. Even though catastrophes and vast art’

of land ami water occur time may be thought of as ecology is not an experimental subject in experiments,," “natural sense; there is no need to connive Situations that do a Baconian not occur naturally in the way a chemist is obliged to com rive conjunctions of materials or oF events that would not come about under natural circumstances. It is a matter of particular satis faclinn ihm ecology now enjoys enough [Hiliiieal clout to insure it against languishing, as do so many enterprises which are thought not to assist the advancement of politicians or of the parties For wineh they stand. movements

ELECTROPHORESIS biological macron inlet1tiles as a rule carry an electric charge, positive or negative EIS I he case may be, and by reason of this property will move in solution toward one nr the other pole of an applied electric held. Electrophoresis MILLS dues For colloidal parti¬ cles what electrolysis does Tor inorganic solutes that undergo Eoiii s' at ion in soluiion. The technique, introduced by Arno Tisc litis, has been of immense help In characterizing and isolating biologi¬ cal macromolecules. An especially useful variant is to bring about electrophoresis in a gel rather than in a liquid; ii is tl urn possible to separate various classes oFeompfmnds by using a sharp blade lo cm the gel 10 lenglhs, one of which may' contain the compound sought .

EMIJRYONIC AXIS

In the course of (heir development ail vertebrate animals go through tin embryonic period known as the neurula. a stage in which the larva has many of the characteristics of a prototypical 75

ENDOCRINE GLAND

chordate. The embryo is an elongated, bilaterally symmetrical or¬ ganism, somewhat flattened from side to side, with a well-defined head bearing paired sense organs, and a spacious body cavity (the coelom) formed as a split within the cells that make up the inter¬ mediate (mesodermal) layer of the embryo, The kidney is shaped from the stretch of coelom connecting the cavities of the segmen¬ tal muscle blocks with the main perivisceral cavity ventral to it. The formation of the nerve tube is described in the entry CHOR¬ DATA. The axial structures are of course the nerve tube and the notochord.

ENDOCRINE GLAND The most familiar kind of gland empties its secretion into a duct that passes from the gland to wherever thr secretory product works, The parotid, a sal i van1 gland, is one of these “exocrine” glands, its secretion passing through a duct into the mouth. The secretions of certain other glands (the adrenal, for exam¬ ple) act sysiemieally and not just locally. Such glands the “endocrines” are ductless and empty their secretions directly into the blood or lymph. Several glands are both exocrine and endo¬ crine: in addition to producing digestive juices, the so-called islet cells embedded in the pancreas manufacture the hormone insulin and secrete it into the bloodstream; likewise, the gonads produce germ cells and also internal secretions affecting sexual develop¬

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ment and behavior.

The evolutionary developments of the several endocrine glands have a number of features in common, one of the most striking being that a number of endocrine glands arc homologues, evolu¬ tionary descendants of organs that have become obsolete. The thyroid gland, for example, which is so vital to the regulation oT metabolic rate, is the evolutionary descendant in modern land vertebrates of an organ that at one time was part of the foodgathering apparatus of the most primitive chordates a mucussecreting groove or gutter in the floor of the pharynx, which served to spread across t he inside of the pharynx the sticky secre¬ tion that entraps minute food particles passing through the pharynx in the respiratory stream. Again, the all-important an-

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76

KN not: KIM, GLANJl

terior element oc the pituitary gland (important because other endocrine: glands arc among its target organs) was at one stage in evolution a functional median nose that passed from the roof of the mouth to the door of the brain. How did evolutionary relics come to acquire a significant en¬ docrine function? It ts most unlikely that endocrine function was acquired dc novo: ii is much more probable ihat the organ simply retained an endocrine function ii a] ready possessed when its primary function became redundant, ft is after ail very likely that many organs have an endocrine function related to their principal physiologi¬ cal activity (as tile ovaries do, for example, and the tcs(es); thus the pharangcal feeding groove referred to above as the evolution¬ ary progenitor of the thyroid gland concentrates iodine as the thy¬ roid does, and almost certainly manufactures a hormone of the thyroidal type, The classic wav (by no means the only one) of demonstrating

endocrine Function is to extirpate the gland, observe the conse¬ quences. and then demonstrate that normality can be restored by replacement of the gland or by injection of an extract made from u. The procedure is of course not feasible when the gland can¬ not be extirpated) either for anatomic reasons or because in its everyday capacity it is essential for continued life. This applies with special force to the liver (very probably the source uf a whole variety of hormones) and to the brain (part of Which, the hypo¬ thalamus* is responsible for sec reting the hormones formerly sup¬ posed to be synthesized in the posterior part of the pituitary gland). In cases such as these, circumstantial evidence provided by microanatomy, histochemistry, and the like may raise a strong presumption oT endocrine function even jf it cannot be proved with the elegant finality' of tilt: procedures that disclosed endo¬ crine function in the adrenal gland, the thyroid, and the pan¬ creas,

It is in accord with our theory of the retention of endocrine function by organs that become functionally obsolete in the course of cvoluliem that the “modern’’ endocrine glands dn very often exercise a function related to (he original function of the organ. Thus the medulla of the adrenal gland exercises much the kind of function one would expect to find in an evolutionary de-

77

ENZYMES

sccndant of a sympathetic ganglion, and the regulation of body salts is a function not unexpected of an organ the adrenal cor¬ tex that may represent the obsolete pmntphios, the first-formed vertebrate kidney. Another curious and unexplained characteristic of endocrine evolution is how frequently it has happened that two endocrine organs of completely different origins and functions have come to¬ gether in the course of evolution to form a single composite organ in the manner of the cortex and medulla of the adrenal gland, the thyroids and parathyroids, and the anterior and posterior ele¬ ments of the pituitary gland.

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—

ENZYMES

Most or the molecular transformations that constitute metabo¬ lism arc mediated through the action of proteins known as en¬ zymes that expedite such transformations so greatly that for all practical purposes they could be judged not to occur at all in the absence of the enzyme. Many enzymes depend for their action on the cooperation of accessory factors, sometimes referred to as oocnzymes, which often have enzymic properties themselves, Trypsinogcn, for instance, precursor of the most important proLein-splitting enzyme of the small intestine, trypsin, is activated by the enzyme enterokinasc. Enzymes by and large art; specific in their interaction with substrate and are very exacting wiih respect to the temperature and degree oT acidity or alkalinity at which they work best. Thus the most important protein-splitting en¬ zyme of the stomach, pepsin, works in a quite strongly acid me¬ dium and hardly at all in an alkaline medium. The molecule upon which an enzyme acts is referred to as ILS substrate, and the accepted nomenclature for enzymes is formed by adding the sulfix -ast to the substrate; thus proteases, lipases, and carhohydrases act respectively upon proteins, fats, and car¬ bohydrates. The term “proteolytic enzyme” Tor a protease is obso¬ lescent, and “protcoclasiic enzyme” is already obsolete. As with all other proteins, the assembly of enzymes is specified by the nu¬ cleic acids that encode the information directing their synthesis. It can hardly be doubted that the specification of enzyme synthesis 7&

ERRORS OF NATURE

is a principal function pf th& nucleic acids transmitted in the germ edls. Mutations that alibet t Iter synthesis of a particular enzyboe will give rise to (he corresponding enzyme-deficiency disease. We have chosen phenylketonuria as an example; i; is caused by a gene which when inherited From both parents leads Lo a deficiency of phenylalanine hydroxylase. In albinism the deficient enzyme is

tyrosinase. Enzymes also have a Wide range of uses tu biological manufac¬ tures, as discussed in our entry on B [< ? EN ( ; i tv EK RIME.

EPITHELIUM

The epithelium is a tissue composed of contiguous cells, ail of the same kind, so arranged as to bound a surface. In its original usage an epithelium bounded a convex stir face, whereas an t?*duthilium bounded an inner nr concave surface. Thus the cornea, the window of the eye, is lined on the outside by an epithelium and immediately behind it the anterior chamber of the eye is liner! internally by an en dot Indium. Otic of the very few respects in which wc have ever differed wit h i lie Penguin Dittiorwtff tyBiofogf is tit at W'C regard the term " in esolheJ turn" as unnecessary and etymologically dubious. (We presume it was so called to distinguish an epithelium of mesoder¬ mal origin a tjtiile unnecessary intrusion of the germ layer the¬ ory- into anatomy.) The cells that form the internal iining of the heart and blood vessels throughout the body are always referred to without fear of confusion as tile “vascular endothelium.”

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ERRORS OF NATURE

The following experiment, which we would prefer had not been done, was carried out on rats deprived of their adrenal glands. The cortex of (he adre nal gland is essential for life, and its re¬ moval or inactivation leads to a rapid loss of salt from the body, wiih fatal results unless a compensatory excess of salt is eaten. When rats deprived of theil adrenal glands were offered a choice

n

I'KtUJKS Of NATURE

between plain and salty drinking water, they drank the latter and survived; but when the choice was between salty water and sugary water, they drank the sugar water and died. The moral is that Nature does not always know best and that natural appetites may mislead. The Arcadian notion that Nature docs know best is widely prevalent; it underlies, fur e sample, the herbalists1 pious belief that Nature is designed to provide from its own bounteous pharmacopoeia of berries, worts, and roots a remedy for all natu¬ ral human af lections. Nature must not, oi'cotirsc, be blamed for our misconceptions of it any more than it can be blamed for the miscarriages of such artificial procedures as blood transit!si on and tissue t rat!sp I a [na¬ tion between genetically unrelated individuEils. Those who persist in their advocacy of the argument from design have a valid case to answer; they must meet an accusation just as Well founded as that repeatedly leveled against doctors whose patients suffer from the side effects of drugs or from anv other misadventure ol sup¬ posedly therapeutic procedures. Many natural adaptations arc strongly contra -adaptive be¬ cause of side effects that make people ill nr make them more sus¬ ceptible to illness than they otherwise would have been. Consider for example those prevalent sources ol hunt at! distress, the aller¬ gies, which in their various manifestations polled or food al¬ lergy, anapliy lasts, the self-destructive autoimmune diseases-— are¬ al! indirectly a consequence of our enjoying an immunologic re¬ sponse system so extremely sensitive and so very well able to discern the Intrusion into the body of nonself substances; no immu¬ nologist would question for a mo in tail the proposition that a rabbit not yet born will be able lo manufacture an antibody against a chemical compound not yet synthesized. Of course, it may properly be said that the possession of an immunologic re¬ sponse system confers upon us and upon animals generally a nft advantage for such a system is essential to life. Although a man or woman prostrated by an asthmatic seizure iriighL t Stink it a life

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not always

worth living, A second, different example of a maladaptive side effect is that associated with human upright posture, which, it has been re¬ marked, may be a constaiiL source of moral satisfaction but has se¬ rious mechanical drawbacks. In most mammals the backbone is a 80

ERRORS OR NATURE

simple un inflected arc running from head to tail a cantilever having the four legs as piers but the upright human backbone has several points of inflection: it bends somewhat foiward in the thoracic cage and in the small of the back and somewhat back¬

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ward in the sacrum. Upright postitfc exposes the backbone to new and evoltitionanly unfamiliar physical shocks and stresses, so it is no wonder that the spinal column has the reputation of being the first struct LIIV in the body to show signs of “aging/’ The great apes, though facultatively Uvo-icgged, avoid many of ihe disad¬ vantages of that condition by using their arms for walking and their knuckles as forefeel, walking characteristically not on the fiats of the feet but on their outer margins. Human beings, w alk¬ ing upright and being squarely liai-footed. are extremely vulner¬ able to such ailments as Lhe anterior protrusion of intervertebral discs and a Variety of back pains of uncertain etiology, A veterinarian once wras deeply enraged by the description of our vulnerability to injuries of the spine as an ‘’imperfection of man*': dogs, he insisted, also suffered from disc Lesions. It is unfor¬ tunate that he so badly missed the point of this description nf a disc lesion (as the maleficent side effect of an adaptation} that lie dismissed the whole argument as yet another Conspiracy to di¬ minish the standing of veterinarians and to deprive them of selfrespect arising from the fact that their patients suffer ailments oT lilt: same kind and degree nf gravity as those that a fillet human beings. He was probably noi appeased when, in correspondence, he was invited in draw a between the maladaptalions otherwise normal human and those that may afflict the beings 0f mutant honors which form so large a part of small-animal veteri¬ nary practice. We must nnt leave this subject without stressing that the net advantages of the upright posture strongly outweigh the disabil¬ ities of the kind we have mentioned: lor the upright posture Liber¬ ates the hands and so makes dexterity possible a p rice I ess pos¬

distinction

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session,

A miscarriage of immunity underlies a third example of maladaptat ion: t he susceptibility! of human beings to hemolytic dis¬ ease of the newborn. This affliction arises because the placenta is so attenuated as tu be permeable by the antiembryo antibodies Lhal are sometimes formed (see our entry on RHESUS FACTOR)

HJ

ETHOLOGY

when at parturition feta] red blood corpuscles escape into the male mat circulation. Rhesus polymorphism may of course confer some advantage that more than balances the wastage from hemolyric disease. It is hard to see w'hat (hat advantage is* because it is noi present in anthropoid apes nor in all human communities. The fourth example is of a maiadaptation of an altogether dif¬ ferent kind: a stale of affairs in which an adaptation that is dearly advantageous for a majority of people is fatally disadvantageous to a few. In the entry SICKLE-CELIi ANEMIA we explain that sicklecell trail is the heterozygous manifestation oT a gene S, which transforms norma! hemoglobin A into an abnormal form that causes the red blood corpuscles to become sickle shaped in deoxygcnaied blood. Sickle- cell trait EK widely prevalent in areas of the world where malaria is or has been endemic, because its victims enjoy a relative immunity from malaria. This adaptive coup ap¬ pears on the surface to be what a chess player would call a “bril¬ liancy11 a perfect example of the wisdom t>f Nature and the be¬ neficence of its designs. Bui alas, there is a dehil entry loo, of just the sort that the amhor of a Bridgewater i realise would be well advised to disregard: approximately one quarter of the offspring oT parents showing the sickle-cell trail will die young, because in accordance with Men deli an rules this is tile fraction that will he homozygous for gene ,V and will suffer from siekle-cell anemia, a

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killing disease. These are all cautionary talcs: they ad monish against imputing to nature a design that would tempt one to infer the existence of an omniscient Designer who is able to foresee Lhe injurious side effects of His arrangements.

ETHOLOGY In the nineteen twenties and thirties the study of animal behav¬

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ior or of that part of it which its practitioners would have deemed to be '1scicIuiÿtc,1 was in a sorry state. Living organisms were relegated to the position of laboratory performers, and ex¬ perimentation look the form ol ascertaining and recording lhe way in which an episode of behavior was influenced by modifying lhe conditions under which 11 was performed. To observe an ani-

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fl2

ETHOLOGY

mal was hot though: i animal had to be pricked, pdked, prodded. or have a bl ight tight shone into its eyes, Whereupon its be¬

havior was modified in a Way that was automatically thought to be informative (though in reality it seldom was). Merely to ob¬ serve an animal, especially in its natural environment, was not rated a scientific activity but rattier an agreeable outdoor pas¬ time, suitable for clergymen on weekdays and (or enthusiastic young mothers inculcating habits of intelligent awareness into 1 heir progeny, The word “ethology’1 is not merely an alternative designation of the science of behavior; it is a term that stands for a genuine revolution in biological thought. Ethology is rooted in the vhitTiatiott of animal behavior, an activity lha! only simpletons think simple. Except in the special case whertt an observation merely confirms or rebuts a prior expectation, observation is a difficult and sophisticated process calling upon all the intellectual virtues; at ten tion, patience, heightened awareness, caution in coming to conclusions, courage in framing expect at ions. Ethologists charac¬ teristically st tidy natural as opposed lo contrived behavior and try also to discern the structurt of natural behavior, that is to say, to discern a functionally coherent, quasi-purposive performance in what to an inexperienced observer would present itself as a se¬ quence of isolated and teleologically unconnected performances. Jt is particularly satisfying to record that the first behavioral study that would be recognised by any modern ethologist as ethological in spirit and in execution was the work of an all-around experiment al biologist w ho had made important contributions to genetics, embryology, and the stud)1 of growth. We refer to Julian S. Huxley’s paper on “The Courtship Habits of the Great Crested Grebe,” delivered to the Zoological Society of fÿondon on April 35 of the society's Procttd&igs, 21, I ill 4, and published in

Study of animal behavior with the iiuenluess that will discern a behavior structure is by no means a matter of passive obser vat Hjn.: it is an exploratory process in which the observer is constantly framing hypotheses, forming expectations about whm is going on expectations which repeated observation! will either uphold or rebut. By such means ethologists have built up an impressive anatomy of normal behavior. Behavior is studied under natural conditions because the interpretation of natural behavior is the 93

F-THOJHOGY

goal of ethology, Experimental interference such as the addition is undertaken only insofar as of removal of one egg from a nest it will throw light on natural behavior. There is no experimenta¬ tion for its own sake to create the appearance of being laudably scientific. Ethology has been more successful on the descriptive than on the causal/explanalory side that is to say, in (he interpretation of behavior in terms of the electric traffic of brain and nervous system, which is not the interpretive level at which ethologists choose to work. Learning and memory do not therefore rank as high on the agenda of ethology as they did on that of the older style of investigation which ethology has largely supplanted. What is happening is that ethology is building up a library of contextually distinctive concepts such as drive, appetitive behav¬ ior, displacement activity, and the like, in terms of which behav¬ ior can be explained at an elhological level much as political be¬ havior can be explained at a political level without recourse to psychological interpretation. If there is human physiology, human anatomy, and human ge¬ netics, why should there not also be human ethology? No reason at all. It simply has noi yet been attempted in any systematic way. When the connection between smoking and lung cancer came to be known, it would have been helpful indeed if ethologists had al¬ ready studied the ethology of smoking and categorized its various forms more rigorously than the familiar but inadequate distinc¬ tion between inhalers and uomnhalers. IL is a job that should be pro fession ally done, though oT course we are all familiar from our own experience with the medically important distinction be¬ tween, on the one hand, (hose who take occasional drags at a ciga¬ rette (leaving it between puffs in an ashtray if they have been well brought up or, if not, over the edge of a priceless marquetry table) and, on the other hand, those whose cigarettes bob up and down in the mouth as they talk (while their eyes smart and blink at the unhllcred smoke that Coils upward from the lighted end). Those who have given up smoking fed like people freed from a tyranny, especially from such appetitive activities as the patting of pockets, the groping in handbags, and the opening and shutting of draw¬ ers that may eventually confirm the dreadful suspicion that they have run out of cigarettes,

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84

ETHOIXJGY

"Olympian glibness” of psychoanalytic interpretations of human behavior have often been held up to public obloquy (see "Further Comments on Psychoanalysis71 in P_ 11. Medawar, Pluto’s Republic (Oxford, 1982], pp, 62-72). But ethology's excursions into I he interpretation of human behavior have been just as glib, and in some ways even mnne culpable because there is a kind of plausi¬ '[’he

bility about l hem which has often taken in the inexperienced or the unwary. We have in mind quasi -ct ho logical interpretations of the origin of human aggression, tribalism, and territorial posses* sivencss. The most confidently self-assured oT these arc something of an embarrassment to old pros among ethologists, who often firmly dissociate themselves from such theories. This is not to say, f if Course, that ihe study of animal behavior throws no light upon human behavior; it would be an inexplicable anomaly if it did not, for human beings evolved from lower animals and much of their behavioral repertoire is homologous with ihat of animals. Maternal care is a case in point, Tor no one in his right mind could suppose that the entire complex repertoire of maternal behavior in human beings arose tie novo with the evolution of man. This is a simple example, of course, because there is so much indepen¬ dent and parallel evidence from embryology, endocrinology, and elsewhere that upholds the homology. From the standpoint that would have been taken by a modem Dr. Johnson or Voltaire, what is most interesting about I he behavior of man is not the part that can be construed as an inheritance from lower animals but, on the contrary, ail the greater and more important pari that comprehends distinctively human practices and propensities such as moral judgment and ratiocination. [t is in any event reassuring to know that, far from being dis¬ tinctively human, play, aggressiveness, bluff, and showing off are pari of a very ancient behavioral heritage. Nor is there any human diminishmcnl in recognizing, as did Darwin in his Descent of Man (London, 1890), that man still bears in his behavioral rep¬ ertoire "the indelible stamp of his lowly origin," The descriptive cthological concepts now to be outlined arose in response to a need and have persisted because they satisfied it. Though many are figurative in nature (a characteristic nut to be avoided in the English language) the terminology is natural and unpretentious and can be understood easily by those who wrish to

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B5

EUGENICS

do so. Drive, for example, is a figure of speech fur the motivation {an¬ other figure of speech) which underlies the behavior that satisfies certain basic biological needs; expressions such as “sex drive” and “hunger drive" have an immediate intuitive intelligibility- A drive tends LO persisL until its goal, a consummtory act, is achieved. Thus the hunger drive is, as it were, switched off by eating and the sexual drive by mating. The kind of behavior that increases lire li kelihood of achieving such a goal is described as appetitive be havior, something that applies literally in the food drive and figu¬ ratively in the sexual drive. It has been a commonplace' observa¬ tion of ethologists that if a drive is frustrated or if an animal is confronted with incompatible alternatives as happened with the proverbial ass that died oT hunger because of its indecision in choosing between two equidistant and equally large bundles of hay then an animal may distract itself by 3 flurry' of activity of

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no obvious functional significance. This is a displacement activity, such as a scientist might be thought to indulge in when, stuck in the composition of a paper intended for a learned journal, lie builds a useless piece of apparatus or carries out a deeply uninfor¬ mative experiment . Doctrinaire bchaviorists arc known to regard this cut ire special terminology as an affront. Persons of more temperate judgment will instead rejoice that the richest and most versatile of all lan¬ guages has the resources for building an apt and unpretentious terminology so well suited to its purpose.

EUGENICS

Most truthfully described as a body of aspirations having os¬ tensibly to do with the genetic welfare of mankind and resting upon the authority of a science (genetics) imperfectly understood, eugenics is now so mixed up with racism that it is difficult to ap¬ praise it coolly. Yet an attempt 10 do so is imperative if we are not to continue at the mercy of amhitiuus politicians who might once again abuse the authority of genetics to promote their mischie¬ vous and illiberal ambitions. The word (for which he at one time used “vir Ecu It ure”) was coined by Francis Gallon (1822-1&1 1), who in I90& introduced

m

KUCKMCS

the notion in the following terms: "Man is gifted with pity and other kindly feelings, ho has also the power of preventing many kinds of suffering, l conceive ii to fall well within his province to replace Natural Selection by other processes that arc more merci¬ ful and not less effective. This is precisely the aim of eugenics.7’ These words, if murmured while gazing at a photograph of Gallon in his prime a benevolent-looking gentleman with ihe air of an elderly London clubman might create the impression that Gallon, deep at heart, was a reasonable and kindly scholar working to spare mankind t he cutting edge of natural selection. Any such interpretation would be wide of the mark indeed: Galton envisaged the development of a strong “caste sense” among the naturally gifted members of each social class, These, the ge¬ netic elite, would have the biggest say in legislation and, where called for, the first claim upon charity. Gallon wrote: “I do not see why any insolence of caste should prevent the gifted class, when they had the power, from treating their compatriots with all kindness, so long as they maintained celibacy. But if these contin¬ ued to procreate children inferior in moral, intellectual and physi¬ cal qualities, it is easy to believe the time may come when such persons would be considered as enemies to the State, and to have forfeited all claims to kindness” {Fraser'’.r Magazine 7 [1873]). So much for all that fine talk about man’s being "gifted with pity and other kindly feelings.” Gallon's is the morality of the gas chamber. The worldly-wise will not think it at all out of character that Galton had an unhealthy interest in the subject of capital punishment, especially in death by hanging {Nature 57 (1897]:79). The supposedly scientific justification of eugenics is a parallel or analogy which we shall show to be deeply unsound. It is the practice of tin: stockbreeder: if the stockbreeder can improve his stock by selective mating, why cannot viriculture do as much for man? The first riposte that comes to mind is that selective breed¬ ing is not the stockbreeder’s only stratagem: he has recourse also to cutting, and this is something that no eugcnicis1. lias had the te¬ merity to propose for man— unless perhaps Gallon believed that the same efTcct would be achieved by the withholding of charity, and perhaps of medical attention, and of anything else entailed by the forfeiture of all claims to kindness, to use Gallon’s own un¬

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happy expression. H7

FAJCRNIC5

The technical objections lo the parallel with stockbreedmg, however, arc more damning scientifically. The elite caste that Gallon envisaged would not be of much use unless its progeny had the same superior characteristics something which, it was confidently thought, could be achieved by bringing it about that members married only each other, because to do otherwise would be to undo the selective work of many generations of controlled

—

matings, The genetic implication here accords perfectly with elementary genetic notions that had prevailed Tor many years, namely that file well-adapted animal was homozygous with respect to the ge¬ netic factors being hred for, and that animals homozygous for cer¬ tain genes mated with others homozygous for the same genes would breed true and produce progeny genetically similar to each other and to themselves with respect to those genes. The elite, then, would be homozygous with respect to the genetic factors that made them so. Unfortunately, this is far removed from genetic re¬ ality. In nature populations arc noi homozygous but quite exten¬ sively heterozygous, although the paticrn of genetic inequality in the population may itself be fairly stable lessons learned from the observations of Th. Dobzhansky, E. Mayr, and many other population geneticists of distinction. The elite thus could not be relied upon to breed true, an ambition that could be fulfilled only if the genetic factors ihai made For eliteness were so few that se¬ lective breeding could “fix” them in the breeding stock in tile ho¬ mozygous state. So far is it from true that the end product of the stockbreeder's art is a homozygous population, that stock breeding is coming in¬ creasingly to rely ujion production and marketing of predomi¬ nantly heterozygous end products, themselves the progeny of a cross between two parental stocks neither of which need he ho¬ mozygous. Indeed, the idea that a superior caste of human beings can he raised up and wrilJ perpetuate itself by intermarriage has no solid genetic foundation: it could be done, of course, if we were content with the fixation of one or two genes thought to be spe¬ cially desirable, but the ambition of eugenicists goes well beyond such modes! procedures. The notions thus Far criticized do not relate to the program that is sometimes called negative eugenics— -the putative improve¬

—

rs

fcLKifcNtCS

ment of the human genotype by piecemeal genetic intervention, especially that which makes use of marriage guidance and genetic counseling, without any element of coercion or threatened with¬ drawal of privilege. Such measures arc preventive: their purpose is, insofar as possible, to prevent any foreseeable conjunct ion of genes that might cripple a child physically or biochemically. Al¬ though some abnormalities respond to this approach (among them phenylketonuria, hemophilia, and Huntington’s chorea) congenital abnormalities that arc due to abnormalities of the chromosomes (Down’s syndrome is the most obtrusive example) form a category apart. There is no doubt that the frequency in the population or Down’s syndrome has been dramatically reduced by a turn of opinion that decreased the mean age of motherhood by five years, Because abnormalities of (he chromosomes and the diseases they give rise to arc virtually irremediable, afllietions of this kind raise all the problems and threats that pertain to feticide, but these arc not the province of the geneticist . His rnlc is, in collabo¬ ration with the plivsician, to draw attention to the facts of the matter and give grounds for forming an opinion on whether or not premeditated feticide is a desirable course of action. Such a judgment would doubtless be formed in the clear realization that no one has conferred upon fir indeed withheld from human beings their supposed right to bring physically or m en tally disad¬ vantaged children into the world. There is, to be sure, sociological evidence which makes it seem likely that modern parents will not stand on any hypothetical right to bring defective children into the world Wc can cite, for example, the popular reaction to the discovery that hemolytic disease of the newborn is most often Hue to incompatibility of rhesus factor; because of the prevalent mis¬ conception that ait children born of rhesus-positive fathers and rhesus-negative mothers will be alllictcd by hemolytic disease (which is by no means the ease), young couples who had been blood-grouped sometimes broke off their engagements.

—

—

We shall now give a number of examples of the forms which ge¬ netic counseling might take in order to circumvent genetic disor¬ ders, Consider first the case of hemophilia, an exceedingly painful and disabling abnormality of blood clotting that makes its victim &9

EUGENICS

a

“bleeder.” hi the most familiar, most thoroughly studied form,

it is a

sex -linked recessive condition in which the victims are mainly male, although the offending gene is carried by females: the working of the Mendehan rules is such that hall the sons of a female earl ier will he afflicted and half the daughters will be carriel's. In such a case the on ly wise and charitable procedure is for the woman carrier of the gene to abstain from childbearing. For somewhat different reasons, an analogous procedure should be adopted with the grave abnormalities that are genetically con¬ trolled by late-acting dominant genes, Huntington’s chorea is one such disease, and because its effects become manifest some¬ what late in lift:, a luture victim may have children before the disease is evident. On average, half the children of a marriage between a normal person and a future choreic will be e a triers of the dominant gene and will be afflicted; the other half will be ostensibly normal. A choreic who marries and has children thus will bring into the world offspring who will either coniract a most terrible disease late' in lile or live in the shadow of a dreadful fear that they will eventually do so. Here too. the only humane and socially jusi procedure is to abstain front having children,

The so-called recessive diseases include phenylketonuria, a principal cause of low-grade mental deficiency, While it is mnsi unlikely that all such diseases have yet been identified, the order of frequency of those (hat are known is IQ 1 (one in lens of thousands).

These conditions arc described as recessive because the gene re¬ sponsible must be carried by birth the gametes that unite tn form (he new individual. In view of the in frequency of mutation and i he infertility of phenylfeetonurics, the great majority of the af¬ flicted will be the offspring of marriages between two hclerozygotes, that is. two carriers of the same offending gene. On the av¬ erage, one- quarter of the offspring of such a union will be normal, on e-quarter afflicted, and one-half carriers like their parents. In the table below we have taken two illustrative frequencies (>r af¬ flicted persons: one in ten thousand and one in forty thousand. By application of the Hard /-Weinberg Theorem, I he frequencies of the heterozygous carriers of the gene will be one in one hundred and one in iwo hundred, respectively. 90

KUGKNICS

—

Frequency of Afflicted p Krrqiÿnty »f carritb Qttterozygoies) Frequency of marri3j£$l between carriers Gene frequency f>

—

1 : 1 0,000 (2/r)“

i :5ff

I ;4f),000 i -r i oo

1:2,500 1:100

1: if),000 1:200

It is clear that if these carriers can be identified (something possible in an increasing number of recessive disorders, but not yet m all), then tire appropriate preventive measure is to discour¬ age marriage between carriers of f-he mtne harmful recessive gene. An eminent anthropologist, anxious to lind fault, construed this recommendation as the truly ludicrous proposal that marriage should l>c di scot i raged between carriers of harmful recessive genes (a proposal which, if pm into effect, would effectively abolish the institution of marriage altogether because nvrjwir is a carrier of one or more harmful recessive gen.es), if the frequency of carriers ol the two conditions we arc considering is one hi fifty and one in a h Lin deed rexpec lively, then, as the table shows, the proportion of marriages discouraged Would be one in twenty-live hundred and one in ten thousand, figures that cannot reasonably be cents tr tied as a serious threat to the liberty of tl«ffi subject or a wantonly cruet deprivation ol a person's supposed birthright to firing physically or menially disabled children into the world. Nevertheless, the procedure is not as simple as it may appear at first sight. It would entail some screening of engaged couples, which could only be dune on a voluntary basis and only when family bis to ties raised the likelihood or even the remote possibil¬ ity that one or the other parent might be a carrier. Genetically, moreover, the withholding of natural selection ean only have the effect of compounding the problem; for although it may be masked in the heterozygous state, the offending gone will con¬ tinue: to increase in frequency through the ordinary pressure of mutation. Whatever problem the gene currently gives rise to will become progressively worse generation by generation. It is not much consolation that before the situation becomes unmanage¬ able, a cure for phenylketonuria will be round; for the cure will not be a genetic cure, but only a synipiomai ic cure which, like the discouragement of intermarriage: between carriers, could prtly be dysgcnic in effect. Eli

EUKARYOTES

The problems of how 10 cope with genetic disorders arc grave and exigent and will become more so as mortality from other causes diminishes. But solutions can be found if tact, humanity, and wisdom are applied. Sec Francis Gallon: The Life and Work of a Victorian Genius by D, W. Kor rest (London, 1974).

EUKARYOTES This term refers to cells, or to organisms containing cells, in the nuclei of which the DNA as a salt dike compound with a basic protein is organized into chromosomes housed within a nucleus separated front the remainder of the cell by a distinct membrane,

EUPHENICS This term is the coinage of Joshua Lcderbcrg and stands for the attempted annulment of the effects of deleterious genes by im¬ provement of the environment. An example is given in the entry PHENYLKETONURIA, where it is suggested that phenylalanine be reduced in the diet of children constitutionally unable to manu¬ facture tilt* enzyme phenylalanine hydroxylase that is needed to m e t abol izc p he n y1 a I a n i nc, Contrary to popular belief, cuphenics does not invariably have dysgenic consequences; some euphonic procedures actually bring about genetic improvement. An example is given under SIUKLECLI.I,

ANEMIA.

EVIDENCE OF EVOLUTION

Various contemporary currents of thought have given rise in recent years to the impression, perhaps the hope, that the notion of evolution has somehow been discredited and that the doctrine of special creation has been reinstated and possibly even put on a scientific foundation. There is no substance in either view, though it is difficult not to sympathize wit li the layman’s bewilderment upon learning that acceptance of the hypothesis of evolution does 92

EVJDKNCK OK EVOLUTfOW

not rust ns lie had assumed it must upon die validity of socalled proofs of ovolulioHj most oT which arc unconvincing or Often to 01 her intirprciatiorts, but rather upon evidence of a dif¬ ferent and Far weightier kind. The host way t-o explain ihc difference is to consider why we behove that the world is “round” (spherical). When bright schoolchildren are first introduced to this notion, tiiey are olfared “proofs” of the roundness of the earthy which in retrospect scent pretty trifling; they are told that when a ship is sighted on the horizon they see first its mammas! or funnels) ihen its Other su¬ perstructures; |in ly laiejf? docs the hud heave in t-o view. This is most unconvincing a mere trick of refraction, perhaps, such as one might expect at the level of the horizon, Another such nugget of evidence is dial If three posts of equal height are stuck into the ground in a straight line, (lit: middle post will look higher than the oilier two (very difficult here to arrange matters in such a way as lo make such a “proof1 technically acceptable), Outside school our belief in the earth's being round does not depend On any OOt or l WO proofs. We accept the: idea because the whole ol navigation, aeronautics, geodesy, geometry, cartography, and chmminiriry rest upon it: it is not now possible to think ra¬ tionally on any of these subjects without accepting the concept of the roundness of [he earth. No scientist need convince himself of the truth of the matter by looking apprehensively— it might be thought —at photographs of the earth taken from the moon. Essentially the same holds for the hypothesis of evolution; op¬ ponents of the idea, who are so often philosophically as welt as sci¬ entifically il literate, think it shifty and evasive to contend that ac¬ cept a tice ol the hypothesis does jrtÿ depend upon acceptance ol certain proofs of evolution; but indeed Jt does not. Wc acxiepl the notion of evolution because it alone makes sense of the pattern of similarities and differences among contemporary living organisms

—

that is revealed by the study of comparative anatomy; of the phe¬ nomena revealed by or implied by von Baer's Law, such as the remarkable similarity between the embryos of human beings, hirds, and reptiles, on the One hand, and on ihc other, the em¬ bryos of their reputed ancestors, sucli as fish. It makes sense also of the existence of what would otherwise be thought of as somewhat anomalous animals with intermediate characteristics, such as

93

EXQGENETtC HEREDITY

feathered reptiles, fish with lungs, or mammals that lay slid ltd eggs. It makes comprehensible too tile evolutionary transforma¬ tions we have witnessed in our awn lifetimes, such as the spread ol i he nielatiic variants of maths in (he countryside near industrial areas. Another example is the evolution in many hospitals of strains of staphylococci or streptococci that are resistant to the ac¬ tion of penicillin and other autibiot ics. Finally, only the theory nf evolution makes a convincing story of the fossil record A man who believes that fossils are the remains ol organisms inundated bv Noah’s flood can believe anything: no effort ol credulity would be LOO much. Only evolution theory makes vestigial structures in contemporary organisms intelligible as, for instance, tile tran¬ sient appearance during the development of higher vertebrates of a median (pineal) eye, such as we find in lampreys. Opponents of evolution often think they have scored a point in saying that ‘'evolution is only a hypo thesis.” Yet the word “hy¬ pothesis” is used in this illustration precisely because it is logically and philosophically the correct term with which to describe a proposition of this stature.* The word has no pejorative connota¬ tion whatsoever: it is a sign of lack of learning to suppose that it

—

has. There arc still many uncertainlies about die mechanism of evolution* and some at least about the enact course it took iti the history of existing animals and plants. Nevertheless, the theory of evolution is scientifically acceptable, is indeed widely accepted: it is the product oT an exercise of mind wholly different from (hat which gave rise to the moving, imaginative literature of the fil’sl chapter of Genesis.

EXOGENETIC

HEREDITY

Exogcn eric heredity is the form of heredity (hat is mediated not throu gji ihc chromosomes but through other generally speak¬ ing, "cultural” means of information transfer. I’hat which is propagated is knowledge, know-how, and various products ol

—

—

[tic loÿicisl position f>( the p JTTUdeduct ivc arifiimtinl from which dcdutliÿ inferences may ho drawn lo sue whether or IIOL they correspond iu rail life.

* h in a provisionally boliovud-in proposition, in

isc of

ii

94

EXOCENbTLC HJiRfeDm

mind such as books, laws, rules of behavior. and mechanical and other inventions. When human an i fat: is undergo a slow, system* atic, secular change generation by generation, as they 61ten do, then we may reasonably speak of an Revolutions an dxogendt ic or, as Alfred J. Lot ha once put It, "exosomatic" evolution. as op¬ posed to evolution of the more lam i liar endogencftc or endossmja-

—

i ic

kind.

Biologists who rate themselves Straightforward, tburfi-rtiindedj no-nonsense people are apt td dismiss the whole notion of exogrnetic evolution as fanciful, woolly-minded, nr (with a certain pe¬ jorative inflection) merely “philosophical." These wise folk should try to keep ii in the forefront of 1 heir minds that the notion ofestogenelic heredity was first propounded by a specially straightfor¬ ward,

tough-minded geneticist

notorious

lor Ins lack of

nunsciisi-

caiiiy. Thomas Hunt Morgan (iBbd 194:")) wrote on the (

matter

bus:

While biologists have come to reject the theory of the inheritance of ac¬ quired characters by means of the germ-cells, nevertheless they recog¬ nize the fact that the human jract has succeeded in another way in transmittingdceriiiin i rails acquired in one generation to the next, "I here are, [Iren, in man 1wo processes of inheritance: out: through the physical COgib nutty of the germ -cells, and [he other through the transmission of ihe experiences of one generation to the next by means of example and by spoken and written language, h is his ability to communicate with his fellows and train his offspring that has probably been the chief agency in the rapid social evolution pf man. hi the animal kingdom we find many case* in which the young are protected and cared for by their parents. Such beginnings furnish the background OMt uf which has evolved the more complex relation of parents and offspring in the human race, where a prolonged period of childhood furnishes excep¬ tional opportunities for the transmission of tradition and experience. Hatis of Evolution [f-ondon: J 9d2], chap. 1(f) [ The

Scientific

'This kind of heredity, and the form of evolutionary change that is mediated through it. are sometimes referred to as cultural he¬ redity or evolution. It is ;ui injudicious designation for it gives rise to the impression I hill what is evolving is culture, whereas the ter¬ minology we have adopted makes it clear thai we an: speaking of a scheme of heredity and of evolution that is mediated through culture. Rxogenctic evolution, while an arresting notion, is also an 95

EXOCtNETfC HEREDITY

obvious one- something dibit moat biologists have come upon or worked out For themselves without prompting from Morgan, Herbert Spencer, or any of the other advocates of the idea. Per¬ haps its very obviousness is what has made it unattractive as a subject of investigation. Exogenet ic evolution is that winch has made man not merely a hut also an aerial, marine, and submarine creature which has bro ught it about that men may live at the equator or at the poles, in space, and one day, no doubt, elsewhere in tiie solar system. It is cxogcnctie evolution too which has brought it about that human sensibilities have been so far refined that by the use of one or a apt her exosomatie instrument we may sec objects many billions oT times smaller than the smallest object that can be discerned by the naked eye anti many millions of miles farther away than the most distant we tan ordinarily see. Sophisticated instruments enable us to sense X mys, moreover, and discern the heat of a candle burning four miles away. Microscopes, telescopes, Geiger counters, clothes, levers, wrenches, hammers, cutlery, and guns are among the exosomatic organs of mankind, and these evolved much as OLtl pWn proper organs evolved. There; arc some amusing and deeply instructive parallels between the evolution of endosur untie and ol exosomatic organs; both arc gradual and both may embody vestigial charac¬ teristics, especially in clothing (one thinks of those long since funciionlcss buttons at the ends of the sleeves of jackets worn by men and of the buttonholes in their lapels). Again, as they wear out or arc superseded or discarded, exosoma tic organs have to be produced again by manufacturing processes anti natural selec¬ tion has some part to play here with respect to their economic fit¬ ness: only that which works and which people want enough to buy will be reproduced anew, and a fresh variant will muon be¬ come the prevailing type in (he population. Red in tooth and claw, i he marketplace has witnessed the complete dispossession by the ballpoint of the goose quill that so long served onr greatgran d parents. Mutation plays in exosomatic evolution a role comparable to the one it plays in ordinary evolution: when Jelm Boyd l.hmlop ( I 840- 1 9Lf 1 ) invented the pneumatic tire, It conferred such a high degree of economic fitness that ii swept through the population of

terrestrial

—

creature,

m

KX0QKN FTrrC H tiREPITY

vehicles of all kinds so rapidly that a vehicle with solid tires has become a curiosity within our own lifetime. These various parallels are not to be rated much higher than fun, bin the: dilfc rentes between exosomaiie and endosomaitic evolution are pro found: lor one thing, exosomatic evolution is fully reversible and for all practical purposes endosomatic eVOlurion is not. Again, as Morgan clearly foresaw, esosomalic evolu¬ tion is in (he baniarddan style, for it embodies a learning process. blndogenetic heredity docs not and what is learned can lie come part of the heritage. The most compendious description of the content of exogenctic heredity is Karl Popper's L'Tlnrd World,” for obvious reasons now referred to as “World 3.’’ (See Popper’s Objective Knowledge [Oxford, 1-95®],) Where World i is tire ordi¬ nary physical world and World £ is the world of Otir conscious experience, World 3 comprises [he products of the human mind the world of memories, programs, rules and instructions, arguments, theories, the content ofbooks, and so on. Tn (he tiglu of this description, essentially Popper's, we can sec the force of Richard Dawkins’ conception of (he meme as a unit of exogen ct it

—

—

heredity. The reaction of many biologists to learning about exogenet ic heredity and evolution is often “So what?” There is no need to elaboraie here upon the answer that it is rh rough cKogenettc he¬ redity that human beings owe the greater pan of their present fit¬ ness and their hope of becoming fitter Still.

S7

FERTILITY In demography “fertility'1 means reproductive performance; reproductive potential or capability is referred to as “fecun¬ dity”- a point worth making, because biologists tend to use these words the other way around. By a natural extension of meaning, eggs arc described as fertile or infertile according to whether they are or arc not capable of developing into whatever they are the eggs of. Matters to do with reproduction arc dealt with elsewhere, so the present discussion will limit itself to problems of fertility as they arise in demography. During the 19305 the fertility of the population of the United States and the countries of northern Europe, continuing a trend that had begun at least fifty years before, sank to so low a level that doubts were expressed about the ability of these populations to maintain their numbers. The “twilight of parenthood” was widely spoken of. and the world’s leading demographer was con¬ fident that the Western world was facing doom in spite of the fact that population numbers were not falling. Laymen in general were not at all alarmed, not realizing that the increase, or lack of decrease, in population numbers was due to the steady accumula¬ tion of people beyond reproductive age. Demographers them¬ selves became very' interested in devising measurements of the re¬ productive vitality of a population, of its ability to maintain its numbers with regard to the prevailing regimen of fertility and mortality. One may ask of any member of the population, for example, wrhat is the likelihood that he or she will be represented by an in¬ dividual surviving to the same age in the next generation? If we ask this question of the female population only, we arc in effect asking, what is the ratio of live female births in successive genera¬ tions? The figure is Robert Kuczynski’s “net reproduction ratio” (NRR). If the NRR is greater than one, the population is more

—

98

KUiUftKS OK SI'KK.CH

holding its aWn; but if it is less than one* the population is declining. Another such measure is Alfred J. Lotl.a’i “true rate of natural increase,,” renamed by R. A. Fisher I litr ‘'Malthusian pa¬ rameter,” which expresses the rale uf Ct>nt umous compound inter¬ (lian

est at which the population is changing in size with respect to the prevailing rates of mortality and fertility. If the value is positive, i he population is holding its own; if negative, it is tint. The attempt to express the reproductive vitality of a popula¬ tion by a single scalar measure as if We were taking its tempera¬ ture -is doomed to failure;! it exhibits the same wide-eyed inno¬ cence as the fervor that has prompted some psychologists to believe that intelligence cart be measured by a single scalar figure such as the IQ, For purposes of population projection demographers have now adopted a quite different method, in which Average i&iipltiedfatuity size is the quantity considered most significant. This scheme of measurement LS much easier to resolve into independent variables that have a real meaning in terms of the way people behave in terms, for example, of marriage age, marriage rate, and pattern of family building.

—

—

FIGURES OF SPEECH

The familiars of the living world have greatly enriched every¬ day speech with met up hors and similes, not all of which are Strictly fair to the organisms that gave rise to them. "To drink like a fish ’’ is based on an obvious misunderstanding: a ftslvs apparent drinking is the swallowing movement by which it keeps up a re¬ spiratory current of oxygen- bearing water through the gills. It is less clear why newts are reputed to be under the influence nf liquor, its in the well-known English euphemism "as overtired as a newt.” We may attribute it to the somewhat tipsy-looking side-to-side moveme tit of the newrs relatively big head, produced by its sigmoid swimming movements, “Alike as two peas” is surely disrespectful to the memory of Abbe Gregor Mendel, whose niche on tile slopes of Parnassus tv as made possible by the i«? likeness oT pea seeds and pea plants. '‘As dead as m Litton” leads irresistibly to the reflection that 99

K1TNI.SS

Cambridge, England. is hardly loss famous for making sausages than as a seal of learning, and that one of the last earthly acts ol Thomas is[.range ways, eponym oT the: famous tissue culture labo¬ ratory on the outskirts of Cambridge, was to culture surviving fi¬ broblastic cells recovered from the inside or nidoaarc of a sausage, 1 hereby showing that individual cells may outlive the organism of which they were at one time a pari. ‘LAs mad as a hatter” is sociological rather than biological: it refers to the menial impairment that was at one tune brought about in battel's by toxic chemicals used in the dressing of fur. “As mad as a March hare1’ may perhaps justly impute madness to the hands single-minded absorption in its mating exeTciitjfe The roe mil men t of new figures of speech find similitudes into Lite English language is a continuous process, ait vigorous today as ever before, When A biologist Hear? someone's table maimers being compared unfavorably with those of a piranha, he or she can at tile same lime hear the little chink which .signifies that biol¬ ogy has dropped another jewel into die treasure chest of the English tongue,

FITNESS The importation into science, with special technical meanings, of word* that have a long history of vernacular usage is a constant source of confusion and embarrassment- The word “fitness" is a ease In point, for only the connotation of suitability or adapiednesx in tin: vernacular usage persists in the technical meaning. The other connotation, which calls to mind middle-aged individuals jogging around the block or taking deep breaths, ill an Qf>cti win¬ dow, is not part of (He technical meaning. i' it ness is the c h a ract eristic of organisms, of populations, or of genes that is maximised by the operation of natural selection. The Quantity or property maximized is net reproductive adorning*, the word “net” emphasizing that the measurement of fertility makes allowance for mortality (see "'net reproduct ioit ratio” under the entry J-TRTIJJTV).

It was this usage of [lie word “fitness” that prompted Herbert Spender to refer to natural selection as the agency that brought too

FORCE OF MORTAL! ]

about L ht: “survive of the fittest/' Intelligent school eh ildre ft are (|uick 10 spot the clement of tautology in this description, which might lie construed to mean the “survival ol those that survive": jt is si shhrnCj though, that those bright youngsters, far from ful¬ filling their early promise, often turn into adults who repeat ihis criticism as if il were original or in any real sense damaging. The notion of net reproductive advantage is explained and exempli¬ fied in the entry having to do .frith NATURAL, SELECTION. A wise biologist has pointed out that net reproductive advan¬ tage is not the only conceivable measure oi fit t less in the more general sense of a dap ted ness: the fitness of a mam moth’s woolly coat might well be measured by its thermal conductivity (the lower the better), but it is still appropriate to say that unless a thick woolly coal had confer riffd Darwinian fitness upon its pusscssors- ir, if we choose to put it that way. upon tin: genes that arc responsible for its formation then mammoths could not have evolved into possession of it, The recently introduced idea of in¬ clusive fitness makes explicit allowance for the fact that the net re¬ productive advantage of a gene Will necessarily include any ad¬ vantage secured vicariously* in [he sense in which parent at rare and certain types of family cooperation may provide for the prop¬ agation of an individual’s genes, "Inclusive Illness,’1 an authority 1 uis written, “may be defined as that property of an Individual or¬ ganism which will appear lo be maximised when what is really being maximised is gene survival,” Because of its adoption into technical language front vernacu¬ lar speech, the Darwinian conception ol'fimess is still the subject of grumbling criticisms. At least some: of these result Irotu a ruisunderst adding of die notion, in particular the belief ih:it fitness is measured only in terms of fertility, witn the implication that all genetic changes that provide full* enlarged fertility must of neces¬ sity prevail.

—

FOKCF OF MORTAUTY The force of mortality is the age -specific death rate. In a popu¬ lation riot subject to senescence (deterioration with increasing age) the forte of mortality will be constant, out in real life the

lt)J

FORM AMD MATHEMATICS

characteristic pattern is one in which the force of mortality starts high in the first year or two of human life because of the special dangers associated with childbirth and extreme infancy, Jt then fails to a minimum at about the age of fourteen or fifteen, the ac¬ tuarial prime of life, in which a human being is more likely to live an extra year or month or day or minute than at any other age. This is the epoch, too, at which a human being’s reproductive value is highest. After this period of prime, the force of mortality ascends inexorably until our closing years, for we do indeed be* come more vulnerable as life goes on.

FORM AND MATHEMATICS

The application of mathematical methods to the description and analysis oT biological form is an enterprise that has had a powerful appeal Tor quantitatively minded biologists. It is a sub* ject upon which two extreme and apparently irreconcilable views have been held. Sir D’Aicy Wentworth Thompson, author of the famous essay On Growth and Form (Cambridge, 1917) wrote:

The study of form may he descriptive merely, or it may become analyti¬ cal. We begin by describing the shape ol an object in the simple words of common speech: we end by describing it in the precise language of mathematics; and the one method tends to follow the other in strict sci¬ entific order and historical continuity . . . The mathematical definition of form has a quality of precision quite lacking in our earlier stage of mere description . . . We are brought by means of it into touch with CJa* lilco’s aphorism (as old as Plato, as old as Pythagoras, as old perhaps as the wisdom of the Egyptians) that (lie liook of nature is written in char¬ acters of geometry- (p, 7 19)

The antithetical view was admirably well put by David Mer¬ edith Scares Watson, one of the foremost paleontologists of the twentieth century in his SilHman I-ccturcs, Paleontology and the Modem Biology (New Haven, 1951): The existence of real, fundamental structural resemblance can only be established by using the intellectual processes which characterise that branch of zoology called morphology. Morphology is a form of logical thought remarkable in that it is not mathematical; indeed, its essential

102

FORM AND MATHEMATICS

elements, being, ax I hey are, qualities, arc not susceptible of tiiathematicn! expression, {p. 33

In the course of the next Few paragraphs we hope to show that there is art element of truth in both viewpoints, Consider first (he mathematical representation of form, ft fol¬ lows from Cartesian principles that' a system of surfaces in space can itt principle always be represented by a system of fund ional and s, the relationships relationships among three variables, being conventionally! expressed in the form F(x, y, z) 0, Thus the horns shown in the left-hand figure below may be represented algebraically by a function =ÿ

[x +

r/? + {z- yy = a{k> -/y\

Similarly, a paraboloid with cusps (center below) and its more artistic representation (on the right) are spatial realizations of the

formula +

*y/ = o.

With ijbcsC examples in mind (all from the Mathematics De¬ partment of the Science Muse tint in Londons by whose kind per¬ mission they are reproduced here), how can it validly be said that form is not susceptible to mathematical treatment?1 W&tSpti was right, though, for m the examples we Itavir chosen, there was no intention of trying to find a mathematical description of given forms sncli as we illustrate. On the contrary, the formulas came first and the figures are simply their geometric realization. Under the influence of the geometers Julius Plflckcr and Jacob S t inner, the spatial realization of complex algebraic relationships

vbl1' H.JLt

FORM AND MATHEMATICS

became something of a cottage industry. It was a pattern Irish lec¬ turer in the old City and Guilds College In London who modeled the formulas quoted in the text: it would be tile labor of a lifetime and require a battery of computers to describe mathematically the shape of even a quite simple organism and the performance of such an exercise would be completely pointless and teach one nothing. After all, it is not very often that we need a minute de¬

—

scription of a given form, More often, especially in biology, what we want to do is compare forms. This is an entirely feasible enter¬ prise mathematically made possible by the method of transfor¬ mations which, with its ancillary notions such as variance and in¬ variance, is capable of throwing light on such fundamental biological concepts as homology, Consider the image oT a lantern slide thrown on a rigid screen, and imagine that the screen is tilted i h is way or that from its nor¬ mal position at right angles to i he optical axis of the projector and the cone oflight that issues from It. Tilting the screen would cut the cone uT light at different angles, and the image projected upon the screen could be distorted in a way and to a degree that would depend on the direction and the degree of tilt; by this means wc could generate a whole class of geometric figures: circle, ellipse, parabola, and hyperbola and in an extreme case, two intersecting straight lints in fact, the conk sections. These are ge tie rated by “projective transformations,” which are susceptible to an entirely precise mathematical definition even if we cannot define mathe¬ matically the form oT the image that is projected (which might he: of a landscape: or a portrait or a whole animal). Change of shape can he mathematically defined, even if shape itself cannot. because it is independent of the subject to which it is applied, a transformation may be thought of as an operation in its own right regardless of its subject. The mathematical expression that defines (lie characteristics of and gives the rule for the operation is known as a mapping function,, as explained in the entry on TKANSIYIRMA-

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—

TIONS.

With the projector model in mind, the distinction between the properties that are variant or invariant under transformation be¬ comes self-evident. The property of being a circle or a square has no meaning in projective space, because under projection a circle becomes an ellipse or other conic section, and a square a rectan¬ gle; however, the properly of being a conic section is clearly in104

IOKM

AM)

MATHKMATICS

transformation. The truths embodied in the theo¬ projective geometry art also invariant under projective

variant under rems of

—

transformation in fact, project ivc geometry is so defined. Two other invariant properties may be mentioned: /;'warily is one, for clou which is straight on the slide wijl be straight on the screen, no matter how we uli it, and certain special ratios such as the Cross ratio or inharmonic ratio arc also invariant . Paraftetism, however. is not. It was an tuiporiani episode in ihc history of geometry when Felix Klein (1849-1 93T>j| defined a geometry as a study of properties of space that are in variant under a specified group of transformations. A “group" of operations in this sense is a set of operations such that the product or consequence ol applying any two operations of the set suceessively is itself a member of the set. Many morphological concepts which we grasp intuitively call lie defined formally in terms of I cans formation theory. Let UJ> ash, for example, what is the minimal affinity that must hold between two forms if they arc to be comparable at all!J This question has a precise answer two forms are comparable when 1 hey are homtoinorf/hic, that is, related in each other by continuous one-to-one mapping lunetions. Cicomet ncnllv this means that the mapping function which defines the transformation and so assimilates the two forms must be such that each point in one is brought into correspondence with one and only one point m the other and that Lhe function is continuous; An intuitive realization of these requirements would lie the transform}!lions brought about in a drawing on a shed of rubber that is expanded or contracted or turned or twisted in any way we please, prt&idtd the rubber is not tons. Figures so related are said to be homcomorphie; thus the two forms immediately below are homeomorphic: so are the next

TO three, all metric relations being now lost. One might well wonder if fligi properties remain invariant under these highly permissive transformations. Some do, for certainly a basic affinity remains: the relationships of i ns i den ess and outsideness, and (lit: relative Kill

K > R M AN D MATH KM ATI CS

placing of landmarks art’ lilt main invariants. $p is Egler’s Theo¬ rem , illustrated by the tirsi sci of hnmoomnrphs: I he number of enclosed spaces plui the number of meeting points equals the number of ffrics plus one. The homologies in these frames are easy to discern.

Contrast

with these sits ofhomeoiuoiphic figures tile ones now

illustrated. No process oJ continuous transformation could Ininsform these into each other. Flirjy are nonhomeomorpmC' ifdib ft; rent lopo logical rank. If these were organisms we eon Id allot

hi

:v-;

j Ultrfhl .

i

tM

,r

1 ; Jj i

Jp1

each one to a diliercnl taxon, Homeomorphy is that very basic si mi lari l y of ground plan which unites the members of a single phylum, an affinity which disregards differences that are not dif¬ ferences of ground plan, In summary, we believe that although the mathematical treatmerit of form as such is usually not possible, the exact mathemati¬ cal treatment of change of form very often is. We also believe that some of the ideas of abstract geometric theory can illuminate the fun da menial biological concepts of morphology. Thus there is a great deal of truth in both bf the antithetical opinions quoted at the start of tins enlryi For a much more sophisticated and versa¬ tile treatment of the mathematics, of form that is still basically

106

KR.AU ns

Kleinian in approach, consult Tkv Fractal GeaimUy Hcnnil 11- Mandelbrot [San FridtisCn, 1902).

of iVatffie

by

FRAUDS frauds in science arc conscious and purposeful misrepresenta¬ tions of tiic truth Ibi' personal gaitfe We cannot distinguish them morally from ordinary crimes that have a scientific setting, such as plagiarism, (heft of data nr ideas, forging of laudatory testimo¬ nials by jobseekers, and so on. Discovered scientific frauds are always considered especially! shocking, and because Only a minority can ever lie discovered they are thought to cast doubt on the probity of the entire scien¬ tific profession (“tips of icebergs" are referred to by people lor whom cliches are a habit usd substitute for thought). Clearly, this is most unfair: who knows how many venal policemen there may be, or secret diabohsts among those in holy orders, or college pres¬ idents secret lv opposed to learning in all forms? Hot we think these are the exceptions, not the rule, JL is not surprising that so many discovered frauds in science are commuted by practitioners of the Life sciences. In the phys¬ ical sciences everything is so much more cut and dried, and the subject matter so much less variable. If a scientist eager for self-ad vancemcm were to publish a fictitious statement about the physicochemical properties of eel yin imeihy hit nmoniurnbro nude nr of triiodothyronine.:, he would not long remain undiscov¬ ered; his claim would be found u> Ilou t some cation of physics or chemistry, and his work could be repeated and confuted with¬ out great exertion. No such comfortable words can be said of the notorious biological frauds: the PI It down skull, for example, which purported to show that England was a cradle not'' merely a throne of mankind; and the deeply discreditable story of the white mouse made tip with a felt-tip brush to create the illusion that it bore a living skin graft from ait unrelated black mouse. The latter was an episode that caused immense trouble to work¬ ers in the same held and diminished the reputation of a labo¬ ratory head to whom I hi: criminal owed nothing but gratitudeThen there was t hi: famous case of a professor of psychology at

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t07

FRAUD® a London! university who manipulated figures relating to ihe IQs of (wins in such a way as to support his belief (hat difference* of intelligence were due in far greater measure than was usually supposed to heredity as opposed to upbringing. His scientific crimes were eventually uncovered by a skillful in vest iga live jour¬ nalist with training in genetics. Perhaps the most notorious bio¬ logical forgery was. that associated with the name of iJaui Kammerer. who professed to have demonstrated Lamarckian inherit¬ ance in midwife loads. No commonplace exp Sail at ion can account for all (hesc frauds, The motive underlying at least three of them was a passion¬ ate belief in the truth and wider-lhan-scienilfic importance of a right-seeming doctrine tit at lay SO far Outside the accepted canon dial it was felt to be I lie subject of unlair discriniinat ion by ortho¬ dox scientists. Indeed, belief m (he Lamarckian style of inherit¬ ance burns in its devotees wiih the kind of intensity (ha> literary people regard as almost a guarantee of authenticity, We have Coleridge's assurance, Us wo had Plato’s, that there is something divine about creative inspiration; some such thought may console the tricksters when they lind that Nature is dragging her feet. Scicnlists have btien pronounced simple-minded and gullible for being taken In by these frauds. There have even been hims that they close ranks and do their best to hush up anything that might diminish their supposedly sacerdotal reputation. This is a very superficial view. It gives no weight to the important truth that science, like banking, politics, marriage, and indeed most human ret at ions hips, can only be conducted on a basis of confi¬ dence. We cannot carry on our life forever on our guard. The field naturalist who shyly brings a fossil to the museum docs not expect to he greeted with ''Another forgery, 1 supposed nor does the sci¬ entist who proudly submits his latest paper to his department head expect IO hear “Lift glad to have your paper; you know what a devoted reader of science fiction T am.”1 Science could no more prosper under such conditions than could a marriage in which a husband late from work was invariably niei by the Words: Forni¬ cating again, Fll bell" _l

Ifl8

GENETICISM A deliberately pejorative neologism, 'genetic ism” stands for the belief that in the shaping of man and of mankind generally, inheritance and genetic endowment are not merely important, they arc all-important. For its practitioners genetic explanations must be sought not only for character differences of the kind studicd by Mendel but for the rise and fall of nations, the stratifica¬

tion of society, the existence of national differences in pronuncia¬ tion (such as the ability or inability to pronounce theta in a way that differentiates it from tela), and most assuredly differences in intelligence. Indeed, in complete disregard of the consid¬ erations put forward in our entry on NATURE, AN3> NURTURE in¬ telligence has been pronounced to be some 80 percent heritable (that is, genetically prescribed). One of the gravest and most widespread aberrations of geneticism is embodied in the belief that if any characteristic is enjoyed by all individuals of the community, it must be genetically under¬ written, Thus, if it should torn out that a certain basic linguistic form such as the Aristotelian subject /predicate form is an element of all the languages of the world, then its usage must be geneti¬ cally programmed. (Some of Noam Chomsky’s writings are not guiltless of this assumption, which is also a disfigurement ofsociobiology as it steers its precarious course between the twin perils of geneticism and historicism.) It may be well to repeat in this con¬ text the reason why this supreme canon of geneticism is not satis¬ factory: ir any trait is to be judged “inborn” or genetically pro¬ grammed, then l here must be some people who lack it. The ability to taste phcnyhhiocarbamidc, for instance, is known to be genetically programmed because there arc (hose who lack it. The practice of geneticism leads to a systematic depreciation of, indeed an active enmity toward, the idea of cultural heredity as described in our entry EXOGENETIC HEREDITY. The impor-

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109

—

GENETIC AND EMBRYOl.OGIC TERMS

tancc and character of cultural heredity were first recognized by Thomas Hunt Morgan, second only to Mendel in importance in the history of genetics. Morgan’s delineation of what is now some¬ times called psychosocial evolution was scathingly dismissed by C. D. Darlington, then professor of botany at the University of Oxford and a notorious practitioner of geneticism. See his review in Nature 27ft (l979):786-787, of Morgan’s Scientific Basis of Evolu¬ tion (New York, 1932). Morgan’s reputation has, however, out¬ lived Darlington’s, and the notion of cxogcnctic heredity will doubtless outlive them both,

GENETIC AND EMBRYO LOGIC TERMS

Biologists in general, and geneticists and embryologists in par¬ ticular, lend to be meticulous in their use of technical terms and shun such slovenly turns of speech as ‘"the gene for albinism” or “the gene for tallness.” Careless usage tends to obfuscate the na¬ ture oT the interaction between the gene and the environment in which ii expresses itself, We therefore include a set of terms used in genetics and embryology' with the explanations wre deem ap¬

propriate. ALLANTOIS The excretion of waste matter other than gases is quite a p ruble m for vertebrate animals that lay shelled eggs. Their repository for fluid or semifluid waste is an embryonic organ, the allantois, that forms as an outpushing from the hind end of the embryonic gut, which abuts into either the yolk sac or the cavity of the amnion. From the way in which it is Formed, the allantois of necessity has an outer lining of richly vascular connective tissue. This tissue plays a most important part in formation of the placenta of the higher mammals, in which an allan¬ tois is also present and where development is much like that of a reptile in its early stages.

Gregor Mendel’s pioneering genetic researches were made very much easier than they otherwise would have been by the combina¬ tion ofluck and judgment that led him to study the inheritance of differ¬ ences between pairs of contrasted characters, such as tallness vs. short¬ ness in pea plants and their possession of yellow' or green seeds, which might themselves be either round or wrinkled. Thus the conception took ALLELE

lit)

GENETIC ANIJ KMIlRYOEOGit: TERMS

in pairs responsible fur root that genetic fEictoix werS essentially a pair of contrasted characters. This state of a I fairs is by no means typical. Genetic factors custom¬ arily form not pairs but sets of which, of course, not more titan two can be represented in any one organism at any one lime. -Stic It sets of characters are referred to as Allelomorphic (Greek aiks = of another sort or kind). Mendel studied the special case of binary allelism, btn mull iplc alleilsm is the more general case: tints the factors bringing about the color dilutions of.'which the extreme form is albinism form an allelic sys¬ tem-

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AMNIOCENTESES This process in solves the withdrawal of a few drops of amnioiie fluid during pregnancy to provide fetal cells that car be cultivated in order to ascertain the structural normality (or lack of it) of the makeup of the chromosomes. Ey sue ft means an abnormality such as Down’s syndrome can be identified before birth. This diagnosis can then lx: made the basis of a decision about the future of the embryo. The pierced LI re, often adapted for the fetuses of older mothers, brings with it the unexpected bonus of informing the parents of the sox of (heir child, thereby enabling friends and relatives to decide upon a name for it. AMNION Although vertebrate annuals are right Jy said to have evolved from aquatic into ierrcsma.1 or aerial animats, none is wholly emancipated, for all vertebrate animals develop in what is actually or virtually an aquatic environment. The embryonic organ that makes this feat possible is the amnion, a hag-likc structure formed front the outer¬ most of the various envelopes that surround the developing embryo, ft is lined with connective tissue, in which run blood vessels connected to the embryo’s heart. These various envelopes enclose a space, i be amnionic cavity, filled with a fluid that is in all respects os¬ motic, ionic, hydrostatic tt suitable environment for embryonic devel¬ opment. The embryo's mouth is open to the a rtUiipfic fluid, which ac¬ cordingly passes freely into the fetal gut- All vertebrate embryos are thus aquatic organisms, Vertebrate animals possesÿiBg an a ran ion arc referred to as antniotes: reptiles, birds, and mammals are so descriijtÿd and the description is jfsxoncrbiically mofe sound (hail ‘het raped.” a taxon into which birds fit un¬

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easily.

Reproduction that is hot mediated reproductive Cells such as spores or by btidding from the parental stock, is know n as asexual. It leads to the for¬ mat iph of clones of organisms of the same genetic makeup as theft pco-

ASEXUAL REPRODUCTION through gametes, but through

111

GENETIC

AND iLMIlRYOl.OGlG TERMS

genilor, si* djiat i hcrj'e is no increase of "ÿciturcio diversity. It is quite coinhence the term ''vegetative muri among sessile animals and in pi a tit s reproduction..11 often used for asexual reproduction in animals. ft is closely related to (he faculty of rcÿcntfjition and naturally lends itself to the formation of colonic* attached to One another, as in enrols and in polyps. It 3-s quite distinct froth parthenogenesis, a variant of sexual reproduction. Twinning of the kind described nsidentioa I in on r del ini tin it of TWINS represents rhe only kind of asexual reproduction found in ver¬

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tebrate animals. ASSORTATIVL MATING A technical term used especially by stu¬ dents of human heredity to refer to the mating of like With like with re¬ spect to s&me specified natural or nu ritual characltifetic. Thus any ten¬ dency of men anti women of similar stain re, intelligence; blood group, rcUtiqfti, or socioeconomic class to mate wiih each oilier would qualify as awfortulive. Mating predilections, whether associative or nonassortativc, clearly have an important influence on the genetic makeup of human populations; orthodox Jews, fin r instance. Would Lore any racial distinc¬ tiveness they still possess were it not that they incline to marry Others of the same faith, CONGENITAL ['HALT Taken Literally, the word 'conge nil id" refers only to that with Which it human being i* born. Common usage, how¬ ever, tends lo restrict the term to departure* from norniaLity. No one is likely ur be grail Red to learn that he has. eongeniial ears. There is a wide Variety of congenital aberra lions, some of which, for- example ANKNCEPI fAl V

and DOWN'S SYNDROME, are tire subject of separate entries.

as genetic linkage modifies [lie law of in do phenomenon of crossing over modifies the principle of; linkage itt (he direction of independent assortment, linkage groups do not typically maintain (heir integrity, for die matching chro¬ mosomes of a pair tend to exchange material and so recombine ihe linked genetic factors of which they are ihe vehicles, a process that enor¬

CROSSING OVER

pendent

Jusl

assortment, so the

mously enriches genetic variance. nOMlNANCE AND RECESSIVENESS If the somatic effect of an allele only shows up when like alleles have been inherited from both par¬ ent x, i he genetic trait for which that allele is responsible is said [ be re¬ ef MW in expression; short ness in pea plant* is a Case in point, one investigated by Mendel. Phenylketonuria in human be i tigs is described as a recessive flisea.se. because LIIC factor responsible for it must be in¬ herited from boih parents if the disease is to become apparent, A gene

M2

GKW-mc

AMI)

RMRRYOEJGGIC TEH MS

which manifests itself tvcn itihen inherited from only one parent is said to be domiitmif in impression, ihos t hr heterozygous progeny of' it cross bet weeri i nil and short jH:n plants wefs found t >y Mendei to be mil, Some human diseases, among [bom. Huntington's chorea, represent the H HJ 1 ward expression of a dominant genii! that is, out that need have been inherited from one patent only. Obviously, dominance and reccssivÿnfiSS do not represent moral valuations: rheyare simpily Statements about the mode of expression of genetic factors, both states tart be modified by other genetic factors- Indeed. genes vvbich are haSfwittY Ixjtwecn domi¬ nant a rtf I rffiissive winch have some ex presLxion In the ptierozygous static may evolve toward complete do mi nance or complete recessiveness of [repression. Although accord mg to tin: book ii should not be possible to distin¬ guish a homozygous dominant front the corresponding lictcro/ygoic, a recessive factor present in the hetcrozyguus sttile may sometimes exert an effect si rong enough to make the heterozygote distinguishable. This applies, for example, in the heterozygous carriers of some damaging re¬ cessive diseases; the heierozygotc "earner1' of the recessive gene nespoiib

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sible for phenyl keipnuria may have it less than normal phenylalanine tolerance 1 11 L i cun he detected by the appropriate clinical tests a con¬ sideration of some importance in the prevention of phenylketonuria by the discouragement of matings between carriers, The ittosi elementary genmic algebra shows that when two hclerozygotesofa genetic ftictor are mated, half their offspring will be heterozy¬ gous, as their parents were, and the other half will lie homozygous fob tilt two genes that entered into the hybrid, the form LJ I at ion being {'ft X 7ij = rr+ >Tt $ k

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4

ENTCLECHV

Aristotle’s "entirltreheia " was that principle oi1 spirit which in lot-ms a si met me and completes it in some essential rcs|H:cl, braking actual that which had previously been merely potential. In his (rilford lectures oi' L S3CJ4.I the renowned (Herman experimental embryologist I fans Dricsch 1941) centered bis doctrine of vitalism on a variant bf the notion of entelediv that retains the sense and thrust of the Aristotelian usage: the organism is something more than its sub¬ stance and form; it is n/nv by reason of its possession of tlii vital principle eutcdcchy. Qur entry on VITALISM di.tcusjtes this- conception. The sense of completion essential to (hr: Aristotelian usage can also be (bund in Paul Tillich's ( I IfEJfj- I 9G5| declaration that courage is the emdechv which completes a man.

EPIGENESIS In their older usages “epigenesis** and “ preform at ion” were opposites; wlteji: preformation implied the unfolding of.a structure

113

GENETIC

AND

EMBRYOLOGIC TERMS

a heady present, epigenesis referred to the acquirement of si met me and differential ion in a system ostensibly structureless, as the egg was though! to be. Now that the egg is known to he highly structured at a molecular level, the antithesis no longer males sense. In the modern usage' "Lcpigejiests'> stands fur all the pipptisses that go into implementa¬ tion of the genetic inAtj&ciions contained within the fertilized egg, i;Gcneties proposes: epigenetic* disposes,” cell, distinguished genetically by A gamete is a possessing hall' the number of chromosomes present in the ordinary sothalic cells of the body. The gametes arc egg cells (ova) in lemales, and sperm in males.

GAMETE

The word “gene’’ WEIS con sideicd by the man who first used it, Ludvig Johannsen, and by Thomag Hunt Morgan (I8fib 7 1 945), 1 he fatuous American geneticist, as a physical embodiment of Mendel’s determinant ‘‘faerrÿrs” in heredityÿ Ft was never! 1 1 dess treated art a gem-tic entity, genctieallv defined. A gene was that which was rcs|ro risible for a unit character-di!Terence in the Me-riddum canon, for example, for tallness as opposed to shortness in edible pea plants, or giecn as opposed to yellow seeds, Thus explained, a gene ap if ion; in other systems it might be defined as a pears as a unit of unit 6f rniitiitihn nr of Ct&ÿnjfg m'r'r. This purely gericiic conccptjorj of 1 lie gene remained adequate lor the interpretation of breeding e\ perdue n is for many years. The absence of a physical del in it ion was not. and was not Thought of as, an impediment to the growth of genetics. 11 was not indeed until die correcl conception of the nature of genes was happened upon (hal a physical delinition be¬ came possible. Genes have variously been (bought of as templates, prim¬ ers. models, or representative samples; as huge macr&molec tiles; as bead-like madias somehow linearly si rung: and so on. Genes are not adequately described by any of these terms, lor genes are nie$j>&- a conception first propounded for chromosomes by Erwin Schrbdinger and for genes by 1 Ians Kalmus in thi' Journal Heredity l (1950); 19, looking for a signal is ;m enterprise very diiferent from look¬ ing fur something of which one might make a microscopic preparation or mi extract or jf solution. As VL-IIII many other quest ions, the answer's. came from molecular biology. GENE

Wilhelm

—

The percent'Age or proportional representation of a gene in the population is the gene frequency, counting its homozy¬ gous representation as two and its heterozygous representation as oue.

GENE FREQUENCY

114

GENETIC AND KM 6 ft Y OLOG I C IKK MS

Thus if A and a designate a pair of contrasted Mrmlelinn genes, in a population in which the genotypes occur in the proportion AA, AA, Aa, An, Aa the frequency of the A is 0.7 and of its allele necessarily (1 - 0.7) = 0.3. Given random mating, these gene frequencies will be indefinitely conserved under the MendeJian regimen of inheritance. The HardyWeinberg Theorem makes it possible to translate statements about gene frequencies into statements about the frequencies of genotypes. In the entries ort MOLECII1.AR MOLOGY and NfCl.fat; we make clear that genetic informal km is conveyed by the linear ordering of nucleotides down the length of the molecule of nucleic acid. Taken in isolation, this statement is no more informative than to say that in old-fashioned Morse telegraphy a message is communicated by the order in which short and long electrical impulses or light Hashes suc¬ ceed one another. In fact, the genetic code is known as precisely as the Morse rendering of "M'aidiv." ( = Mayday), the international signal of distress. In the genetic code particular amino acids arc specified by a triplet of nucleotides; as there are four different nucleotides, sixty-four different triplets are possible. There is therefore some synonymy in the coding system, even allowing for special signals such as “message begins” or GENETIC CODE ACIDS

“message ends,” The genetic code and the main lines of its transcription and transla¬ tion into the distinctive structures of various proteins are the same in plants, animals, and bacteria. F.vidcntly, then, it is a very ancient inher¬ itance of the world of living tilings. GENETIC DKirr Most theorems in population genetics assume as a baseline for the norm that the members of an imerferiile population mate at random, so that every member has an equal chance of being counted among the ancestors of future generations. The Hardy- Wein¬ berg Theorem makes it clear that when mating is random and the popu¬ lation is equally divided fry sex, the gene frequency remains constant and so also do the proportions of the various genotypes, We may. how¬ ever, envisage two kinds of divergence from this stale of affairs. The first is when the departure from randomness is systematic and leads lo an in¬ crease in the proportions of one gene or genotype as a result of natural selection or of the repealed reintroduction of a gene into the population as a result of recurrent mutation. The second kind of departure is ran¬ dom; it occurs when the vagaries of random sampling create a situation where one gene is represeiutd in the filial generation more often or less often than one would expect in a strictly random mating. If chance has it that such a departure from randomness occurs in the same direction in

115

GFNETEC AND EM11RYOLOGIC TERMS

frequency in the papulation several successive gcnefsiiijns. then the may change through the operation of chance alone. This phenomenon, known as Kinetic drift, has been though I to be very Important in small populations, In large populations the chances of being counted and of not being counted among the ancestry of future generations tend to equal izeL T here is now not much doubt or much reason to doubt that drift occurs, but the magnitude of the effect and the scale of its cont rib tit ion to evolutionary change arc still in question. The notion of drift was vig¬ orously opposed by R, A. Usher, who held the lowest possible opinion of Sewall Wright (mainly, wt believe, because of jealousy), Wright was a principal pioneer of population genetics. His English contemporaries were in the main a rancorous and disputatious lot not big enough, most of them, to allot credit elsewhere than to themselves. Mendel’s theoryT Fisher declared, could have been propounded from first principles, anti in any case the results he professed to have secured were in A statis¬ tical sense too good to be true.

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The genetic system of a species is the whole of that which provides for the transmission of genetic information from one generation to lire nest. A most important element is the mating system, whether it involves inbreeding or out breeding and whether or hot it em¬ bodies any element of assortative mating. The pattern eif chromosomal behavior is of course another element in the genetic system for exam¬ ple, the frequency of crossing uver,

GENETIC SYSTEM

—

GENBT1C VARIANCE The moiety of the variance of a population that arises from genetic differences between its members is known as the genetic variance- If the measurable properties of the members of a popu¬ lation are expressed in terms of deviations, positive or negative, from theif mean value, then the variance of the measured characteristic, nec¬ essarily a positive quantity, is the mean value of the squares of the de¬ viations from the mean, En Mendel i an heredity there is no tendency for genetic variance to decline from generation to generation, as it would if blending inheritance were the rule. This is the theorem of the utmost im¬ portance in the Mendclian theory of the evolutionary proCcssA genome is the genetic apparatus of a species considered as a whole and as characteristic of it.

GENOME

GENOTYPE AND PHENOTYPE An organism’s phenotype is its Overt and manifest character makeup, whereas its genotype is its genetic com¬ position in terms of Mendclian factors or genes or whatever term may be used for the material genetic determinants. The distinction is of crucial

116

OKNKI K: AMI KMBRVCM/MIKÿTKHMS

importance in genetics and practical breeding, Thus an organism that is heterozygous for a dominant gene may have the same phenotype as the homozygous dominant, hut breeding experiments soon show that their genotypes arc entirely distinct. HARDY-WEINBERG THEOREM The population geneticists1 prac¬ tice oT thinking in terms of gene frequencies has struck many naturalists

as offensively abstract, hut the algorithm embodied in the Hardy- Wein¬

berg Theorem makes it possible to translate statements about gene fre¬ quencies imo concrete statements about the frequency of occurrence of particular genotypes. Consider a pair of contrasted Mendelian genes A and a present in a population in the frequencies p = 0,7 and q = (l p) = 0-3 respectively, The Hardy-Weinberg Theorem stales that in a random mating popula¬

—

tion, equally divided as to sex, the three possible genotypes A A, Aa, aa will be represented in the population in the frequenciesÿ-, 'Ipq, q~ respec¬ tively. Then the genotype frequencies will be AA, 0.49; Aa, 0.42; aa, 0,09, These frequencies remain constant from generation to generation, ex¬ cept insofar as some impressed "force’ f such as natural selection is

brought to hear on the population for evolutionary theory.

—a finding of immense importance

HETEROZYGOSITY AND HOMOZYGOSITY

When two like alleles

are inherited from an organism’s two parents, the organism is said to be homozygous with respect to that ailele. Thus, to choose an example of Mendel’s, if 7’and / stand for the genetic factors determining the charac¬ teristics of tallness and shortness res|wctlvely In the edible pea plant, an organism with the factor makeup TT is said to be homozygous for Tr and if its genetic makeup should chance to be ft then homozygous lor f. The makeup Tl-—resulting front the union of gametes bearing unlike fac¬ tors is said to be heterozygous or hybrid with respect to those alleles.

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HYBRID VIGOR The accession of physical vigor (especially fertility, longevity, and resistance to disease) that is found in the progeny of crosses between inbred or partially inbred organisms is known as hybrid vigor. Explanations rtf the phenomenon turn upon the restitution of a predominantly heterozygous state. It (bus applies with special force when two inbred and predominantly homozygous lines are crossed, but the concept has no application to crosses between members of different human populations, each of which is likely to be adapted to its own en¬ vironment and in any event predominantly heterozygous, l hc special mythology associated with “purity” of breeding and hybrid tty by the lay

117

GENETIC AND EMBRVOLOG1C TERMS

public and among people with a predilection for eugenics is a rare mud¬ dle with no solid scientific foundation fta in (he belief fostered by boys’ literature that “pure breeding” is an assurance of courage, fortitude, and all manly virtues, whereas hybrids or ' half-castes” may he confidently assumed to be cowardly and treacherous.

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INBREEDING AND INBRED LINE The mating system in which a lineage is perpetuated by matings between siblings that is, between brothers and sisters, or between parents and their offspring is known as inbreeding. The most extreme form occurs in those plants in which selffertilization is possible (in most hermaphrodite animals it is not). The effect of inbreeding is to increase homozygosity, leading eventually, per¬ haps, to the establishment of a pure line. Inbreeding may have the effect of bringing together somewhat deleterious recessive genes in the homo¬ zygous form in which alone they can exercise actions normally masked by wild-1 ype dominant genes, Thus inbreeding leads, as a general rule, m some degree of genetic deterioration an immemorial empirical ob¬ servation of stockbreeders, A degree of inbreeding (as in cross-cousin marriages) takes place in some human communities, and different reli¬ gions vary in their permissiveness with regard to the amount of inbreed¬

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ing allowedA lineage is inbred when the members are for practical purposes ge¬ netically uniform and as homozygous in their genetic makeup as inbreeding can make them. The progeny of a cross between two such lines, while also genetically uniform, are heterozygous with respect to every gene by which the two inbred parental lines differ. Inbreeding is a procedure fraught with difficulties, leading as often as not to the demise of the inbred line through the accumulation in it of loo many harmful recessive genes, no longer masked by wild-type dominant genes. Fertility, in particular, is often so severely impaired that it is sim¬ ply not feasible to continue to propagate the inbred line INDEPENDENT ASSORTMENT A gloss on the law of segregation, independent assortment affirms in microscopic terms that when chro¬ mosomes of matching pairs separate at gameie formation, they enter the scsrcral gametes independently of each other in random allocations. The same is true of Mendel's hereditary ’'factors’1 when they arc born on dif¬

ferent chromosomes. LARVA Any embryonic form that represents a well-defined station in the course of development may be referred to as A larva. Thus the terms bfastuta, gastruta, and murvla are used in entries having to do with

lift

(Jl'NKTlC:

AND EMBltYOLOGEC TLKMS

development

of chojgatc animals. All arc commonlv referred to as larvae, although nonj| is SIT independent free-living organism, The word is niosi common Iv apgjied, however, to some independent free-living organism iLiat more nr less radically From the adult and is traths formed into the adult by a proportionately radical rrj&tainorphosis,, the most familiar examples being die caterpillars, grubs, and maggots that arc so often the Larval stages of insects. Many larvae (specially those of sessile animals and of parasites serve a distributive the

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function. Larvae as such do not reproduce (but see the entry on NIUTI LHY) and are producer! anew only through mediation of 1 lie: adult. In some orga¬ nisms, jtidrs?d,a larva may in some nebulous sense be as "important" as the aduh- .nd an object of ar least equal zoological interest. $uch a judgment might be held to apply, for example, to the mayfly larva, for tlto ephemeral adult mayfly lives only a few hours anti is in effect a re¬ productive organ of the larva. It is a corollary of von Hirer's Law’ (hat (Lie larvae of related forms tend to resemble one another much metre closely than the respective adults into which they develop; in a number of large groups characteris¬ tic larvae often bet rat1 the affinities of ilteir respective adult forms (see, for example, oiir entry on BAkxÿCLL'sJi Crustaceans typically hate a naifplius larva, J no Husks a 1 rooliophore larva, and sea urchins and their relatives a pluieus larva. The most famous larva of all is, of course, the {involving as it tadpole of frogs and toads, the metamorphosis of docs extensive retrogressive changes, especially of the tail) is oncL of the minor miracles of nature. The ascidian tadpole is thtL mobile Larva of sea squirts anti their kin. so called because of its relatively large head anti relatively long wriggly tail. It is widely thought pf in [he form which by fleoteny became the ancestor of higher chordales. Larvae, it should be added, are subject to select ion pressures peculiar to themselves and can undergo rpme a high degree of independent evoJut ion of specialisations that often have to do with distribution. An ex¬ ample is the long sticky thread attached to the to-called glodiidium larva of the swan mussel. LINKAGE formally sjH'akiiig, linkage is a modification of the law of independent assist i men t. The segregation of Mendelian factor® and 1 licit random arid independent entry into different gametes occurs only when the factors under investigation are carried on different chromosomes, a simpler situation than that which obtains normally, For chromosomes arc (he vectors of more than one genetic factor anti such factors (end to

119

t;t:JVL

HC ANiJ

EMERYOiiatGBB TERMS

be inheriied en bloc in so-called linkage groups, of which the micro¬ scopic cf|ijivalen[ is a chromosome,

MUTATION Mutation is t he inception of inheritable variation. whether in (he germ cells (germinal mutation) or in any ordinary body cell that is capable of division (somatic mutation), thus giving rise to a mutant clone. The physical basis of mutation is a structural change in one or more of tile nucleotides that encode ihe genetic iitst ructions con¬ veyed by DNAa or it may cake the form of a structural change ijri a chro¬ mosome. The changed form to which a mutation gives rise is known as a mutant for instance, a mutant gene or. by extension, a mutant orga¬

nism.

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gene is an allele of the wild-type gene from which it repre¬ departure. The wild- type gene is .toroei itues for convenience signifietl by the symbol +. Mutant genes breed true, of course, but may undergo a further mutation either lo a new allele or 10 the original + form (back mutation). Mutations occur "spontaneously that is, from unascertained causes a1 a frequency of the order of one in tens of thousands of gametes, this frequency being increased by ionizing radiations such as X rays and gamma rays and by a variety of chemical substances, notably by alkyl¬ ating agencies. All subst ances 1 hat react with br upon DNA lend to raise the frequency of imitation also. Such agents arc nonspecific in that they do not cause one mutation rat iter titan another. The randomness of mutations is a source of consid¬ erable disquiet to amateurs df biology, yet it is fundamental to an un¬ derstanding of evolution theory to realize dial as mentioned in the entry on I.AMAKCKISM ''mutations do not arise in response to an orga¬ nism's needs nor dir I hey, except by accident, gratify them.” It is not quite fair TO say that mutations are the ‘raw material of evolutionary [hange,’1 for that sounds as if evolutionary innovations had to await the chance occurrence of a suitable mutant which, If favorable, would then be received into the genetic establishment, A more exact formulation would state that mutant genes provide for genetic diversity ami that, tilirred into the genome by sexual fusion, crossing over combi ned with A

nuttani

sents a

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ordinary Mendclian segregation yields a vast spectrum of genetic varia¬ tion i hat is the subject of selective discrimination. It is not a defining characteristic of mutations that mutants are dele¬ terious, bui they often are and noi surpri singly, considering lhai they represent a disturbance in (he existing genetic equilibrium; nor is it a defining characteristic of mutants that they are recessive in expression, although they often are. According lo R. A- fisher's original theory,

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120

GENETIC AND EM HR YOIJOGIC TERMS

mutant genes arc, generally speaking, “completely dominant " That is, they haw some expression in the heterozygous state, whereupon they may evolve into dominance or rcccssivcncss of expression according to whether or not their cHbcts arc favorable. ONTOGENY AND PHYLOGENY Art organ ism’s ontogenesis is, Liter¬ ally, its coming into being, and its ontogeny is it* development consid¬ ered abstractly and as a whole. Its phytogeny, by contrast, is its coming into being its the course of evolutionary descent and thus may he taken to stand Ibr its evolutionary history considered abstractly and as a wrholc. The Law of Recapitulation is sometimes compendiously ex¬ pressed in the form “Ontogeny recapitulates phytogeny,” OOCYTE The egg cell or female gamete, known as the oocyte, lias only the haploid number of chromosomes. It contains only one chromo¬ some from each of the pairs characteristic of the female's tissues (a numl*er restored to the regular, or diploid, condition by union with a sper¬ matozoon itself containing I he haploid number of chromosomes). The size and structure of oocytes, varying enormously from one orga¬ nism to another, depend on the amount of yotls the egg cell carries and on the number and nature of the protective envelopes around the egg. Some eggs are almost yolk free, and ihe whole substance of ilie egg after subdivision into cells participates in the development of the embryo; but the eggs of amphibians, reptiles, and notably birds carry yolk which in the course of development is relegated to an extraembryonic position, until it is enveloped by cells of the embryonic gut and thus can be used up during development, In heavily yolked eggs only a polar cap of the egg cell, the germinal disk, participates in the formation of the embryo, The egg of the ostrich must be the larges! of all cells. Unlike spermatozoa the oocytes of invertebrate animals are not re¬

plenished, Generally shaking, there is a finiie allocation of oocytes at birth and this is used up throughout life. Under these circumsiances any arrangements will be selectively advantageous that increase to a maxi¬ mum the likelihood of fertilization of the oocyte, then safeguard ii dur¬ ing the lirst few days of life. There is a premium too on prompt fertiliza¬ tion of an oocyte that has been shed. Emil Witschi and others have shown that the fertilization of overripe eggs may lead lu a variety of de¬ velopmental abnormalities. Ii is the evolution of sexual cycles ihai has maximized the chances of fertilization and embryonic survival. There is another sense in which “young” eggs are preferable to older ones: in view of the formation of a complement of oocytes at birth, it is clear that the oocytes shed by older mothers haw been longer at risk of

L2l

GENETIC AND EMBRYOLOG1C TERMS

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IO all influences inimical to eggs among them ionizing radia¬ tions and toxic chemicals, from the influence of which the oocyte may not be wholly sequestered. There is ample evidence that chromosomal abnormalities, especially those that give rise to Down’s syndrome, are more common in the children of older mothers. Ordinary' (fraternal) twinning also is more frequent among the offspring of older mothers than among those of younger mothers.

exposure

OUTBREEDING The stale of affairs characteristic of most free-living organisms in which mating occurs between organisms that are not sibs or blood relations, outbreeding is often enforced by genetic or develop¬ mental mechanisms in hermaphrodites and sessile organisms which might otherwise be especially prone to inbreeding.

At one time a popular experimental stratagem, para¬ biosis is an inelegant and generally speaking uninformative procedure in which two animals arc joined surgically in the hope that their blood cir¬ culations will fuse and become confluent. Our newer knowledge of transplantation has made it clear that if the partners in parabiosis arc genetically different, no effective vascular union can be achieved, for each partner then is an allograft upon the other. Almost anything that can be done by parabiosis can be done by simpler and more effective methods involving the use of cellular transplantation. PARABIOSIS

PLACENTA The higher mammals, accordingly described as placental, arc distinguished by the possession of an embryonic organ the pla¬ centa that is the medium of nearly alt physiological transactions be¬ tween the mother and the fetus, providing for both respiration and nu¬ trition. The placenta is formed by the apposition of vascular embryonic

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membranes to the wall of the uterus, the apposed surfaces being multi¬ ply convoluted in such a way as to greatly increase the area of the fron¬ tier between mother and feius. Placentas are, as it were, opportunistically formed in members of all classes of vertebrates except birds. Considered as an abstract point of design, a placenta might be formed by one or the other of the two ex¬ tremely vascular organs that are attached to, are part of, but lie ana¬ tomically outside the embryo, namely the allantois and the yolk sac. Pla¬ centas are of both kinds, and both may be found among the marsupials: the marsupial cat, Dasyurus, has a yolk sac placenta, and Perameics, the bandicoot, has an allantoic placenta. The higher mammals have allantoic placentas, and at one time it was taken for granted that the allantoic placenta was the medium for all

122

SQE.N ETIC AND EMBRYO I -OTIC TliUMS

physiological transact ions between mother and Ictus. It Ims become in¬ creasingly apparent ihat the yolk sac is also an important pathway, especially for mammal antibodies entering the fetus in kangaroos in particulars instead ofa placental arrangement, mtltitivt secret ioii of the uterus is taken up directly into the yolk sac. From iho way in which it in formed, the placenta must be partly ma¬ ternal and partly fetal in origin; the feint element I hut is most closely apposed to the tissues of the mother is not richly endowed with those an¬ tigens tli a t in organ grafts arouse a rejection renctinn, for this and other reasons a mammalian fetus is not treated as a foreign or no mid I' body and is not i niiLuuu hlogjetjlly reject edy though there are certain circum¬ stances in Which embryonic ingredients can immunize the mother (see i hi i

r entry on

KIIKSUS

FACTOk),

Polymorphism is the stable subdivision of an inpopulation into different genet ie types which [end to maitt* laitt their proportions froin generation to general ion and which arc such that even I lie least frequent variant occurs too frequently to be ac¬ counted for merely by the pressure of current nuuation. Familiar exam¬ ples are the subdivision of human Ijeings into the blond groups A, Ik All. and O or into the types broadly ejcscribejSjias Rhesus positive and Rhesus negative. I -css familiar is i he subdivision of populations of limn an beings and (>f ntii:'.: into difleiciit t issue transplant ai inn groups, [hose desig¬ nated IILA and Hi! respectively. Other polymorphisms are tin1 ability Lind inability to taste the compound phony it hiouiea (pbi-nylihitKarbamide), which to some people is tasteless attd to others so we are told very biller. .An oilier and theoretically very import an I example of poly¬ morphism is i he subdivision of the populations in West Africa and the Mediterranean basin into people who have either normal hemoglobin (A) or the abnormal recessive variant (Sh which ui an i tests itself as sick ic -eel I trait in hcicru/wcues or as sickle-cell anemia in Sb homozyPOLYMOK THIS M

1 r:t breeding

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The anomalously high frequency of what ary sometimes extremely deleterious genes and the stability of pr>!v morphism from gehtrai iori to general ion ]>oint to a genetic enforcement, lor which! then: arc several possible mechanisms. The variants, for example, may be mutually do]>endent for I heir own perpetuation. Such is the ease with sexual dimor¬ phism, which is genetically enforced. The more Usual State of affairs!, however, is where polymorphism is in¬ evitably kept in being because a hcteroxygoie enjoys a selective advan¬ tage over either of the cr espondittg homoiiygoijÿ forms (see tsiCKUvi;3:ci. ANKA.UA). If the heteroy.ygntcs predominate, their progeny will be

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123

GENETIC AND

K.MllRYOIjOGiC

TERMS

homozygotes acid heterozygotes in equal numbers, A st.rlf-]n;rptji iiji.* injj ad vant age is bv on means always apparent and sometimes is more the product of wishful [binking (ban of any ade¬ quately demonstrated net reproductive advantage. Polymorphism, at any rate, is not a rarity or a curiosity but part of the texture of alt normal population*. Polymorphism of genes coding for Structural macromoletu les is found almost wherever it is looked for, a circumstance that easts doubt on the orthodox belief that heterozygous advantage is always the cause of polymorphism. state of alfciin;.

POPULATION GENETICS There was a gem tine theoretical revolu¬ tion in biology when, [be population-genetic conception of evolution supplanted the genealogical or dynastic conception. The latter had been

difficult to overthrow because of the ingrained habit of envisaging the course of evolution in terms of a family tree (“Fishes begat amphibia, amphibia begat reptiles, and reptiles in their [urn begat on (he qne hand Population genetics birds and on the other hand mammals changed all this. That which evolves is a population, not a pedigree and tit EI t which results from e volt it ion is not a diHercnt organism or & new “‘type,* but rather anew population of which (he members have a spec¬ trum of genetic makeups (hat provides for superior adaptation to what¬ ever the selective forces, may have been. This WEIV of looking at things is entirely different from that figured in the' enliven nunai genealogical tables of evolutionary descent and is discussed further in the entry on

SEG REG A" II ON Expressed in microscopic rather than in purely ge¬ netic terms. Mendel's Law of Segregation slates that in the formation of gEtmeleH (he chromosomes of a matching pair pare from each other and enter separate gametes. In genetic terms, the factors responsible for the

delcrm ina tion of pairs of contrasted characters in Mendel's classic ex¬ periments (round vs, wrinkled or green vs, yellow seeds; tali vs. short plants) enter into different gametes. The segregation of genetic factors in gamete formation, followed by the random reunion of gametes at fertil¬ ization, makes possible the genetic recombi nation brought about by

sexual reproduction. SEX DETERMINATION Scmeiimes taken to refer 10 I lie ascertain¬ ment of sex, sometimes to the prior choice of sex, find sometimes to tlic process that causes an animal to belong to one sex ruthenium the other,

sex determination'’ is a very ambiguous phrase. We shall begin with he third sense.

11

i

J >4

GENETIC AND GMBdVOLOCilC

I tKM.S

111 vertebrnics tlif? primary differential inn c»f xi-x is brought About by the segregbUon of a supernumerary pair of chirm inhumes known as die se-x dimmosomes iti distinction li) (he cnlicrs, L lie: (worries,'1 whiÿft perform ordinary somatic functions. In mammals generally, it rid cert airily iti human beings, the male sex is distinguished bv jwjsseision ofnn unequal pair of sc* chromosomes, design ated X and Y. The tin a Id geno¬ type With respect to sc* is then XY, but the female genOtvpe is MM., the female has ing two like chromosomes. In gamete forma tioti in males, the sex |hmmosome5i Like the Eiutnsomes segregate, that is, they pan from cacti other so that two classes of sperm are formed in approximately cqtial numbers; X-biearing sperm and Y -hearing sperm, Here the male is she hcierogamet ic sc*. The female, being homogametic, produces oo¬ cytes that all bear an :X chromosome. It follows that upon fertiimition there is an equal chance of an egg's being fertilised by an X-bearing sperm., giving rise to a female, or by a Y> bearing sperm, giving rise 10 a male. This explains the rough numerical equality of the sexes at concep¬ tion. In some main nulls the Y chromosome is. absent and the genotype of die male is accordingly represented as XO, The heterogamet ii: se* is obviously the sex-determining sex: in mam¬ mals the male, but in birds the female is the sex- deter mining sex. In mammals it is evidently upon sperm that any operation must be carried out if one sex is to be produced rather than (he Other This is a matter of some importance in livestock breeding, and no elTort has been spared in attempting to separate male-determining rr-om female-determ ini tig sjienn for purposes of artificial in seminal ion. iÿl though miracles of ingenuity have been performed, tiie efforts thus fur haw been to no avail. As to the ascertainment of sex tide Unit of the three meanings dis¬ tinguished above), i his is iriside ptissjftfe by identification in embryonic cells of i lie Barr body referred to in (heCH ROMOSOMEX entry. The ascer¬ tainment of sex is usually a bonus consequent upon ihe prec a Lit ionary use of amniocentesis.

Tiie median ism of sexual dillcreniiatinn is such as to yield a sex ratio rtf I Op: I Op at Conception, but i lie sex ratio is different OL hirtit and changes throughput life, predominantly because in. tiiem and at all times from birth on the male is in many respects csjieciatly in resis¬ tance to infection- more vulnerable than the fens the. Thus it comes about that widows greatly outnumber widowers and iti genera) elderly women are much mom numerous than elderly men. In human beings males mu number females at birth to a degree which seems to depend upon the general stale of health, age structure, and well- being of the population. Under favorable conditions (favorable iti other than actuar¬ ial respects) the sex ratio may rise to as high as idle! 00. It has been

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125

GENETIC AND EMBRYOLOG1C TERMS

common experience that ihe sex ratio increases in favor of males during and immediately after major wars. Several explanations have been pro¬ posed, the most popular being that the especially high proportion of young brides and young mothers during and after wars, and hence the more favorable uterine environment, has the effect of sparing the more vulnerable males among the fetuses. The underlying assumption here, yet to be demonstrated conclusively, is that the primary sex ratio (the sex ratio at conception) favors males. However that may be, the effect of a relatively high sex ratio at birth is to bring about an approximate equality of the sexes during the procreative years, an equality which though highly desirable in a monogamous society is fairly often dis¬ turbed by wars, migrations, and other demographic movements. A combination of all these factors, especially emigration of males, brought it about that in Victorian England women of marriageable age vastly outnumbered possible mates, thereby leading to a cruel excess of unmarried females; this was the great age of governesses and nannies, who were often painstakingly made to feel the supposed inferiority of their position. Sir YV. S. Gilbert, whose glib doggerel was set to music by Sir Arthur Sullivan, gauged the sense and manners of theater audiences perfectly by regularly making a butt of aging, unmarried women with mat ri moil ia I aspi rat ions. This and related aspects of his character com¬ bined to make Gilbert one of the most disagreeable figures in the history of show biz.

Together wiih ''sibling," “sibman,” and “sibness,” the word “sib” (meaning a blood relation) poses something of a philological puz¬ zle. Although it is an ancient word with recorded usages going back to the thirteenth century and although it fulfills a function not discharged by any other single wrord, it simply has not been received into everyday speech even indirectly, that is, through professional usage by psycholo¬ gists, anthropologists, geneticists, and the like, If a child today were asked “Have you any sibs?” he or she would probably not understand the question, “Have you any brothers or sisters?” is the almost universal form. We have little doubt, though, that the word would be in common use if it had appeared even once in the King James Bible. Jt doe's appear in the Lindisfarnc gospels (the English translation of the eighth century' A.U.), but that is hardly enough to familiarize the English-speaking world with the word. 51B3

Unlike most mammals, human beings normally give birth to their offspring one at a time. But twinning is not uncommon, and twins

TWINS

126

CKNET1C AND HMRRYOIjOGIC TERMS

are of two kinds. hirst there are ordinary or fraternal twins, which arc in effect littcrmates. the products of two separate eggs separately fertilized and separately implanted into the uterus. from the way in which they art: formed, fraternal twins arc genetically quite distinct and, age apart, resemble each other no more closely than siblings of separate birth. Al¬ ternatively, twins may be of the kind described as identical: these derive from a single fertilized egg, as if the two daughter cells produced by the first division of the -zygote had separated and developed independently. Earring genetic accidents, such twins are of necessity of the same sex, both kinds of twinning may occur in the same pregnancy, and multiple births (triplets, quadruplets, or quintuplets) are often the consequence of both fraternal and identical twinning. Thus two siblings among triplets may be identical and the third the product of a separate fertilized egg. The processes that give rise to the formation of identical or monozy¬ gotic twdns do not invariably go to completion. If they rlo not, twins may be born that are not fully separated. These, through a variety of etymo¬ logical misadventures, ;ire often referred to as Siamese twins. The degree of their attachment varies greatly from tw in to twin; sometimes they are conjoined abdomen to abdomen or back to back, and sometimes they share a common rectum, Identical twinning is the only form of asexual reproduction found In vertebrates, li is exploited by the nine-banded armadillo and by the drmadilhdae generally, for their offspring normally ittclude a cluster of identicals derived by division from a single fertilized egg, Ordinary fraternal twins may or may not share a placenta, that is, they may or may not be synchorial. Cattle twrins invariably are. The bloods of synchorial twins often commingle freely, though of course each circulation is separate from that of the mother. When this occur*, each twin becomes a chimera: each contains its own red blood corpuscles ad¬ mixed with corpuscles belonging by right to its twin. As Francis Gallon was the lirst to foresee, twins are profoundly useful in attempting to distinguish the relative contributions of nature and nurture to human character differences. The observations possible in theory -and sometimes also in practice are of classic simplicity of de¬ sign: the differences between identical twins who have been brought up apart from each other in different environments and exposed to different educational influences may not unreasonably be attributed to the en¬ vironment, that is, in a general sense to nurture. Conversely, the differ¬ ences between ordinary twins neared together arid insofar as possible in a similar way are confidently attributed to differences of their hereditary makeup, Such studies can be useful when the observations arc carried out with scrupulous honesty and when valid techniques ol mensuration are used,

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127

GlvlMlUS AND INSANITY'

It is especially LLjifrii'iujialc. therefore, that the most fajnous and estoisibly (he most extensive of all Gal Ionian twin audits ill OHO undert akrrn by Sir CyHI Bun were of very t|ue-s dutiable probity.

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YOLEC SAC In vertebrates (hal lay shelled eggs, the yolk is contained wit hiti a double membrane known as the yolk sad'. Anatomically -speak¬ ing, (he yolk sac is an extension of the embryonic gut. Its inner lining is con (muons with lhat of ihe intestine?* and its outer lining is a connective tissue richly permeated by blood vessels connecting with the embryonic heart. Volk sacs do not have to be filled with yolk to be so described: one of the most important Ways in which mammals betray their reptilian an¬ cestry is by the possess ion of (his sac, which plays an iinpurtaot pad in tin: nourishment of the embryo and in its physiological exchanges with the mother

ZYGOTE A zygote is the reproductive cell formed by the union of male and female gametes, in which the regular diploid number of chro¬ mesomes is restored.

GENIUS AND INSANITY The idea that there is a close connection between genius and insanity is a philosophical vulgarism. Its main interest lies in how it has come to be accepted into the conventional unwisdom. The best-known formulation of the idea in which, as it scents to us, more attention is paid LO meter than to sense- is John Urydcn’s: Great wits to madness sure ire near allied And chin partitions do limit' bounds divide.

have had the notion from Seneca. Indeed, it goes back to Aristotle and to Plato's Divine Rapture of Creativity. Cesare Lombroso was among the first to propose that there is a psycho¬ logical correlation between genius and insanity but Henry Mauds ley Stoutly denied it; the whole history of the idea is one of asseveration and counterasseviiraiion . It is a literary rather than a psychological notion; Pascal, for example, yvrote, Ifextreme esprit Drydcti is said in

de t'exlTeme fohe. Where all is asseveration and cuunterasiSiCvtralioii, one cannot do better lhan lo turn to someone of Strong, broad understanding;

est

12&

GERM LAYER THEORY

and who qualifies better than Samuel Johnson, who L n Ins t.ift. of Coivlty wrot C| “The true genius is a mind of large general powers accidentally determined IO some particular direction.” This was also Charles Lamb’s opinion in his essay “The Sanity of True Ce¬ il i us," Surely he spoke with some personal authority because of the severe madness in his famiiy; he hilmsdtf periodically lost his senses.

Most of the evidence I hat purports to support the correlation between genius and insanity exists in anecdotes or reminiscences of men or women of enormous ability who have been n euro Lie or hypomanic in disposition. But i I this method of inquiry is pressed to its limit, we can as easily establish a correlation beuccen insan¬ ity and second-rate genius; men such as Fried rirh Nietzsche, Rob¬ ert Schumann, and Charles Lamb were oriented indeed, but not to a degree tit at would tempt us to describe them as geniuses. Yet might they not have been so if their wits had not been to some extent deranged? It is still difficult to understand why (he notion, which seems on its face to be self-coni radict 017, should have caught oh so readily, Perhaps it is because it scents 10 give a certain countenance to dullness: "1 may not lie very brilliant,” someone of slow wits may say, “but at least I’m not out ol my nund.”

GERM

LAYER THEORY

Formerly one of the theoretical pillars of classic descriptive em¬ bryology, the germ layer theory states that the fundamental tec¬ tonic of animal embryos is one in which the cells of the embryo arc organized into epithelial sheets, cell layers, or cellular leases or envelopes, each oi which lias a definite and prescribed fate in terms of the adult structures it eventually gene rales. There arc three layers, and the first two arise as follows: when a fertilized egg has conic to be subdivided into cells, the solid ball of cells usually hollows out to form a Hind-filled veside known as the blastuta. In the next stage this hollow ball caves in at one pole to form two layers, the inner layer enclosing a tube, the primitive gut, iv Inch communicates with the outside through an a perl u re that persists a.s ihe anus. The outer of the two layers of.cells is the 129

CJLRM 1J\VER THEORY

ectoderm, which, being the interface between organism and en¬ vironment, not unnaturally gives rise to the skin and sense organs and the entire nervous system. The inner layer, the endodenn, gives rise to (he gut and to all organs (such as the liver) that begin their life as cellular out pus flings from the gut. Between these first two germ layers various cellular movements in the embryo form a third layer, the mesoderm, which gives rise to (he segmental mus¬ cles, the skeletal structures of the body, the musculature of the gut and body wall, and the connective tissues. The cavity within this middle layer forms the principal body cavity or coelom, from which the kidneys develop. The great appeal of the germ layer theory' rested upon its being thought that the formation of the three germ layers in develop¬ ment recapitulated the evolution of animals generally: thus the most primitive many-eclled organisms, it was reasoned, would hr hollow balls of cells like the biastula, and this would be succeeded by a two-layer structure such as that, basically of polyps and hydroids, forming a two- layered or "diploblastic" grade of organiza¬ tion. 1'hcn, as with embryos, a middle layer would he added, giv¬ ing rise to a “triploblastic” grade of organization. While the germ layer theory' is no longer given much credence and the adtdt organs or tissues to which the various layers give rise are not as constant as they were formerly supposed to be, the element of truth in the theory is now clearly recognized. When Wilhelm Vogt developed the technique of marking areas of the embryo with harmless dyes m order to trace their movements in the course of development, it soon became clear that early em¬ bryonic development is very largely a matter of the movement rel¬ ative one to another of cells and groups of cells. Such movements can take place only if the substance of the embryo is orga¬ nized into cellular leaflets or sheets which can slide or creep over or between one another and which by outpushings and intuckiiigs, expansions here and contractions there, lay down the funda¬ mental structure of the adult organism. The elder Oliver Wendell Holmes (1846-1933), professor of anatomy and physiology at

Harvard Medical School, likened the process to the operations of a glassblower. Thus the germ layer theory ultimately is a theory about developmental tactics rather than about developmental strategy,

130

QON DIVAN A LAND

GONDVÿANALAND Until the Iasi quarter of the nineteenth ceuttlry the notion of r her fixity of continents (that the Continents always were whcrtiLang? Thcv were shielded, we believe, by the ancient conception of a gmti chain of bung, or great ladder of being. Iti Plato’s view, nothing could more clearly manifest (fie operations of a rational divine power than a universe in which there could be found an actual reprcscnintive of any being that might be rationally imagined. Such a scheme would be imperfect if there was anywhere a gap: (here must be a contin¬ uous gradation of creatures from the simplest and humblest all the way to the divine. 'fills was an extraordinarily vivid, persuasive, and long-lasting notion: it is perhaps the deepest root of the idea of evolution, which in a sense is the great chain “temporajized,11 as Arthur O, Lovcjoy* puts it spread out in time- The chain Underlies tile metaphysics of Leibniz arid the metaphysics of Teilhard dc Char¬ din as lie propounded il in his incoherent rhapsody, 77tr Phenamf?-

—

rwti

of Man.

Whatever the place of the great chain in the pedigree of thought dial Culminated In the evolutionary conception, it pro¬ vided also a spiritual antidote lo the impiety ol rebutting the idea lu

* Evi«ytlrte ftho wrik's oil thuConCcpi of I lit' gVtWL eha.ii! tiFtn'iiin is tlrefjJy in debt Llivm’i Qtjal Chain of Bring; A Study of the ffisloiy of in i Idar «. i EI I niÿljlL', Maasa-

eJuist-iis.

193©.

13.3

GROUP SELECTJON

of special creation. For if every conpeivablc kind of organism batl boon Specially created, would not an omnipotent Creator, an¬ swering to platonic expectations of (lie power of divinity, create every possible organism without gaps so that the existence of in¬ termediate and, in the evolutionary view, transitional forms (feathered reptiles and egg-laying mammals, for example) would be seen as the expected and natural product of a great Designer? Voltaire in his Philosophical Dictionary gave some thought to the great chain of being and Was dissatisfied with the clement in it that Lovejoy called the ''principle of plenitude'’ the principle that t here are rio gaps; alt that can be imagined must be. Voltaire disagreed. Is it not obvious, he asked, that (Here is a gap between monkey and man? Is it not easy to imagine a feat her!ess biped, intelligent hut wordless and unlike us tn appearance, which we cart train and which wilt answer our signals and which will serve us? And can one not imagine still other intermediates between these new beings and ourselves? Voltaire’s servile mutes can indeed be imagined: Ii. G. Wells dsd so anti even named them: they an: tin: Morlocks of Wells’s 7 I’m* Machine.

—

GROUP SELECTION

It is usually an individual organism, in population genetics a gene, that is taken to be the subject of natural selection that is, the element that does or does not enjoy a net re prod tic Live advan¬ tage. We need not be so restrictive, however: any sets of replicat¬ ing or replica Led entities between which t lie re are heritable differ¬ ences may be the subject of natural selixtiton. Selection of this kind is described as group selection; ii is appealed to repeatedly to account for the evolutionary origin of properties that relate to the interactions of organisms, particularly those characteristics that benefit the group as a whole, There was at one time a danger that the concept oT group selection would reintroduce 111L0 evolution theory the kind of explanatory glibness that was a weakness ol I he older Darwin¬ ism, Inn modern population geneticists now stand shoulder to shoulder in repudiating the notion that "for the benefit of the

—

134

GKOL'I' SELECTION

-specic-s” is cxplanaiion enough for the evolution of any character trait, even if it is one that mav to .some degree- -however small be disadvantageous to individual members of the group or species, A concrete example will help to make the concept plain. Con¬ sider two different populations of staphylococci such as might be found in neighboring hospitals. Bacteria like these are under con¬ stant and heavy selection pressures; they are not welcomed by hospital authorities, who do their best to make them feel un¬ wanted, and they are assaulted at all times by a variety of antisep¬ tics and antibiotics. Under such circumstances only those staphy¬ lococcal populations can survive whose members arc mutable enough to throw up variants conferring some measure of resis¬ tance to one or another antiseptic or antibiotic. The minority so endowed will be rapidly expanded by selective forces until they become the prevailing type. Thus with hindsight we can say that only those bacterial populations survive whose genetic systems, especially with respect to mutability, make them versatile enough to cope with new selective pressures and hazards. In the outcome, then, this is group selection, though what un¬ derlies iL and makes it possible is of course the orthodox Darwin¬ ian selection of the individual organisms of which the groups arc composed. Nevertheless, in a world in which the elements were just such groups or populations, evolution would to outward ap¬ pearances be Lamarckian in style; that is to say, groups would seem to have undergone a heritable transformation by a specific adaptive response to an environmental change. It would be tire¬ some to press this point in the context of group selection because it is so obviously “Darwinian7* at heart. Nevertheless, a distin¬ guished physical chemist, C. N. Hinshclwood, proposed in the 1930s that if wc regard a bacterial cell as a population of enzymes or of their replicating vehicles, an ostensibly Lamarckian adapta¬ tion of bacterial cells might be underlain by a straightforwardly Darwinian selection in the enzyme population of the cell, but what wrould the selective force be? And by what properties would an individual enzyme be advantaged in such a selective process? Hinshclwood had a good point, and if the term “group selection’’ had been current at the time, lie would have recognized in it a certain kinship writh his own ideas. 135

GROWTH,

LAWS Of*

GROWTH, LAWS OF BIOLOGICAL Two laws will be formulated here. 'Hie first is that biological growth is fundamentally of the multiplicative type.; for l lla l which results fmm biological growl h is, typicallyÿ hself capable of grow¬ ing. This property plays an important part m del r minting die most appropriate form in which to represent size as a function of age. If IF represents size (weight, ti umber, or a linear dimension, as the case may be) and / represents an organism’s age, then we may represent size as a function ol age in the alternative ways repre¬ sented by the two columns in the figure below. We may, on the one hand, plot against age the sum of all the increments of size that accumulate during life and so generate a straightforward curve of growth in which the arithmetic quantity plotted against age is idffl. or, more simply, W as in (ft). This curve of growth al¬ ways lias a point of inileciion, at which die growth rale stOjjs in¬ creasing and starts 10 go down. The point of inflection therefore shows up in the curve of growth rale {b} as a maximum and in the curve of acceleration (t) as its point of intersection with the lime axis (acceleration = 0). In spite of (he si might forty ard appeal of tile Curve ol growth and its derivatives, most si indents of growth have thought it more informal ive to ploi the curve vYsprcij#:growth- In this formulation the quantity We plot is not the simple arithmetic value IF but the accumulated increments of size considered as a proportion of the size already achieved. We plot, in fact, the (integral quantity Uw/w, more usually written Jog,, IT. The three curves spec i lie growth (ff), specific growth rale (r), and specific acceleration ( /")ÿ-are illustrated in the right-hand column of (lie figure. The curves have been plotted from an equation for ihe Grnnperiz, function (see the last line of the accompanying table), but the scales nT the ordinates have been adjusted to make the height of each graph uniform. The table demonsi rates the analytic properties of the three functions most often and most successfully used to represent the course uT growih of single organisms or oT populations. J.’he Iasi eniumn illustrates (he second of ihe Iwo laws that embody the most general Statements wc can make about biological growth. This second law is that the specific acceleration of growth is al-

—

J3fi

GROWTH, LAWS Of lllOIOGICAL

W

bgW

(d)

W T

t

dW

dipjw

it

"dt

tb) t

t t

+ d:W dt!

dt1

t

to

(0

ways negative. We shall name (his Minot’s Law, for reasons ex¬ plained in ihe entry on AGING. Combining the two laws into a single statement, we may say that although biological growth is fundamentally of the multiplicative type, living systems progres¬ sively lose the power lo multiply themselves at the rate at which they were formed. The sense of choosing the logarithmic plot (d ) in the figure as opposed to the straight forward arithmetic plot (a) is made espe137

Function “Mono-

Linear form

Equation

-

molecular”

w

Logistic

W=

Gompertz

W

—

be lost in the course of a dear relationship between the endocrine ninetion and ihe neu¬

rological function of the hypothalamus. The hypothalamus is a center of heal regulation: the tuber cinfreum of the hypothalamus domains temperature-sen skive cells that monitor body temperature continuously. Localization of function in the cerebral cortex was discovered by the electrical stimulation of various points of the cortex in the course of surgical operations. In like manner, localized stimula¬ tion of the hypothalamus has disclosed the wealth of autonomic} functions and the feelings and notions that go with them that are under hypothalamic control. 'These include, for example, the;

—

—

whole gamut of digestive, digestive, and excretory fu net ions. stimulation nl the hypothalamus may bring about sniffing, licking, mastication, swallowing, and eventually defecation. Stim¬ ulation of distinct areas of the hypothalamus produces feelings of intense hunger or satiety, the former so exigent that even well-fed animals may be induced it] rat voracious! y, the latter perhaps opening the way I oa pharmacological I v rai iona! meihod nf diet¬ ing, in which control is not so much of eating as of the inclination to cat, It is known that destruction of the satiety center leads to morbid overeating {hppetpkeMa') . Stimulation of othett centers in the hypothalamus p invokes fear, rage, aggression, extreme plea¬ sure. and sleep. Cerium hypothalamic injuries can lead to the dis¬ tressing syndrome of which many medical students must have thought themselves victims: periodic somnolence accompanied by [.oral

iUOrbid hunger. Study of the hypothalamus provides abundant information that is relevant to understanding the cerebral physical events that accompany acts or staLes of mind. Though they may help to ex¬ plain changei in states of mind, they eannui explain the states themselves: extreme fear is no mure explained by an electrical commotion in part of die hypothalamus than the sensation ol redness can be explained by a train of impulses in the optic nerve 147

HYPOTHECS AMD THKOKV

that is relayed through various substations to the temporal Lobes

of

(he

cerebral cortex.

HYPOTHESIS AND THEORY

In a philosophical vocabulary these words have precise mean¬

usages. We lihjai] attempt to expound them in order to caution biologists against such tin happy lit isu ndersland¬ ings as that referred to in the entry EVIDENCE OF EVOLUTION especially the idea that the word ‘‘hypo thesis” has a pejorative connotal ion . The declarations or propositions from which logical inferences arc drawn are variously described as premises, hypotheses, axioms, or postulates. All have the same place in logical aiiatoriiy, but different words distinguish the way in which these statements c;imt: into being and the degree oT confidence we feel in their em¬ pirical rightness. Needless to sav, these differences show up in Li nguistic usages: we assert postulates, venture to propose hypothesesÿ assume or assert axioms, or take their trulh for granted I typo theses play a special role in science, lor they are the portal of entry of imaginative thought. A hypothesis is an imaginative preconception oT what ihc truth wight be, We belie ve m hypoth¬ eses until we have reason to do otherwise in Immanuel Kant's sense of the wort! belief (“a kind of consciously imperfect asseni”). Charles Sanders iJeirce (10dM-UJ14), (he ffrrcmosl American logi¬ cian of bis era. was quite clear t hit without hypothesis there could be no advancement of science, and Karl Popper said the same. We cannot come to an approximation of the truth unless we begin with some preconception ol what the truth might be. ll is ihc essence of Popper’s philosophy that science advances by means of a continuing duologue between conjecture and refufeilitmr between the formulation ofhvpotheses and their testing by obser¬ vation and experiment, as a consequence of which we either cor¬ roborate the hypothesis or are given reason to modify it . When a hypothesis is corroborated, we gam confidence ibji and can. so to speak, put it m fora higher examination. In a Forma! logical sense hypotheses may sometimes be disproved, but there is ILO logical procedure by which a hypothesis can be proved true. A theory is a hyj>o thesis together with that which i[ logically

ings and

correct

—

>.

148

HYmTHKSIS ANU THW>K> it is a hypothesis pins the deductive inferences we draw from it. It follows, then, that a theory cannot be logically proved to be true a point upon which Popper was perfectÿ clear and so was Peirce f ‘the conclusions of science make no pretensions to he i tig more than probable," he wrote). Hypotheses are, of course, imaginative in origin: We do not deduct: hypoth¬ eses-- for a hypothesis is that front wljlph we draw deductions, Hypotheses are guesses and may of course be judicious or injudi¬ cious, foolish or wise, acceptable or not. The system of hypotheses acceptable at the moment forms what iis hi effect an 'establish¬ ment” of received beliefs, of interpretations and theoretical con¬ structions, that together constitute what Thomas S. Kuhn has called the prevailing “paradigm," a word that would not have caught on so readily if it had not fulfilled a need. Nearly till scientists believe that there is a clear-cut distinction between ftid and theory. The fact or the statement that embodies it is simply an affirmation of "the case,1’ of that which is, purged of interpret at ion and theory, William Whewell (1794 1886) denied that any such sharp distinction existed and insisted dial interpre¬ tation and theory arc Woven into our apprehension of supposedly plain facts at every level. In a finely reasoned passage ending with

entails, that is,

—

—

the words "There is a mask

or theory over

the

whole face of

na-

“Most men are unconscious ot the perpet¬ lurc/' Whewell ual habit of reading the language of the external world and translating as they read'1 (The Philosophy of the Inductive Sciences [London, 1837], voi, l,sec, 4), Tlie construction oT a theory is made possible by the existence of an underlying -system o! conventions or understandings that re¬ late to the meaning* of the terms used, the processes of sen fence transformation, and their use in logical deduction. These consti¬ tute the metathevry, of which there arc two main elements: logical syntax has to do with the rules ol deduct iotig Stfnaflies relates to the meanings of terms and the conventions embodied in defining, that is, in the replacement of one or more terms by others. The element of met at henry which enter* inln science at all levels is that which has to do with truth. Truth is a muialheoreticai con¬ cept because if is sentences or declarations that are or arc not true, and any statement that a sentence is a truth or n fit!site is meta¬ linguistic in other words, is a statement about a staieineni. The umiHivc meaning of empirical truth is clear enough: the slatewrote,

—

Nil

HYPOTHESIS

AJVIJ THEORY

men! l‘thc platypus lays eggs3' is true if and only if the platypus lays eggs. The formalization of this intuitive conception in an ad¬ equately rigorous way was Allred Tarski’s greatest contribution to logic {IjUgic, Semantics and Meitnna 'hematics, inins. J. II. Woodger [Oxford, 1956], chap. SI). The acceptance or reject ion of a theory, and therefore of the hypothesis of which it represents the deductive elaboration, is very seldom a matter of merely pronouncing it to bo true or false. This volume makes mention of a number of bold hypothesis: the hypothesis of evolution, the hypothesis of1 continental drift, (sec dtwrm-'AN'Ai.ANii), and the hypothesis (see RIJOOD AND ITS dTltCUI.ATtOM) that there is an ancient, dark, and mysterious affinity between seawater and blood such that it is proper to describe blood as an evolutionary descendant of seawater. The lirst two are widely accepted, but the third hypothesis is Taise and today is Only entertained by amateurs nr bv naturephilosophcr.x with a taste for obfuscation. The idea is rejected be¬ cause it turns nn a subsidiary hypothesis that is plainly untrue, namely that before the vertebrates left the sea, their blood or that of their ancestors had been in ionic and osmotic equilibrium wiih seawater. On the Other hand, the theory of evolution and that of continental drift an: both received ihisirics, mainly hccausc of 1 heir huge explanatory compass. both do far more than explain the facts they may have been formulated to explain facts such as the complementarity of the Atlantic coastlines of Africa and South America, the former CXJH tenet: of a feathered rcpjtjic such as arehaixipleryx, and the present existence of a mamma! that lays shelled eggs outside the body. The very least we expect of die hy¬ pothesis is that u elucidate what it was set up to explain; this cor¬ respondence does not in itself entitle us to say that it has a great explanatory compass. The enormous virtues of ilu: theories of evolution and of Continental drift are the number, variety, Eind unexpectedness of the phenomena ihcv explain. Some biological theories (we think especially of the germ layer theory and the theory of recapitulation) are definitely not true in (he forms in which they are usually propounded but have remained in the repertory; st> to speak, because there is an im¬ port am clement of truth in them; it is instructive to see how they came to take an unacceptably dogmatic form and LO

—

150

HY I'O'I'H

IS

AM)

THEORY

ask what steps should be taken to rehabilitate them, Scientific research is m>t a conti miing clamor of affinnatftm and refutalion, but Something much more tentative anti consciously explore atory in character. Outright refutation of a theory, therefore, is rather rare.

151

I

LLNESS

Every culture, no doubt, has its theory ofiilness. In the Western world generally, and perhaps in all countries where a JudcoChristian morality prevails, it is the punishment theory of illness that has taken hold: we are ill because we have done wrong, or some¬ times because our parents have done wrong. The punishment the¬ ory is an extrapolation to disease of such homely observations as those which connect stomachache with eating injudiciously, hangover with excess drinking, and syphilis with venery. The punishment theory is deeply erroneous and can sometimes be very cruel. The idea that prolapse of the uterus is a conse¬ quence of sexual overindulge nee has already been cited as an ex¬ ample of Aristotle’s gullibility and his habitual confusion between what is true and what ought, he felt, to be true. The punishment theory is a natural ally of the belief that sexual activity, being pleasurable, must be deleterious; not so long ago the idea that women had sexual desires and derived pleasure from their gratifi¬ cation was repudiated as a '‘vile calumny,” and until recently generations of schoolboys were solemnly warned that masturba¬ tion might make them go blind and perhaps even mad. The liberation of mankind from the Hark superstitions em¬ bodied in the punishment theory of illness may be rated one of the greatest benefactions of medical science. People become ill from a variety of reasons, none of which can be construed as retributory in character: dietary deficiencies; infections by bacteria, protozoa, and viruses; ma I functionings oT (he endocrine glands such as those that give rise to diabetes; Addison’s disease; and cretinism, the consequence of chronic thyroid deficiency. There is, incidentally, an element of charity in describing these last vic¬ tims as cretins, for "cretin” comes from the French ehriiun, meaning Christian. “The implication in this word,” according to lexicographer C. T. Onions, “is (hat these beings are human, although dwarfed and deformed,” There is precious little charity, 152

LMMLJNJTY

thdUgbi in l h-C interpretation of congem Lai deformity as a pUrtLshmem of the parents: ii is intolerable that superimposed on [IK: shock and corn inning tniscrv of giving birth to an abnormal or retarded child, the parents should be obliged to search in them¬ selves for explanation of 'ft misadventure that was probably dug TO chromosomal accident, ail un lucky conjunct ton of recessive genes, or a chromosomal aberration caused perhaps by ionizing radia¬ tion. Although in the main the theory of illness to whieh modern medical science has accustomed us has been liberating and benef¬ icent, its tendency to depreciate or obscure the in fluency of states of mind on stat us of health must count against u. I' he in 11 Lienee of psyche on soma has been recognized with varying degrees of con¬ viction in resistance to some infections (notably tubercular), in coronary heart disease, and even in cancer. It seems to us that a doctor who pooh-poohs or dismisses altogether the notion of an interaction between psyrchc and soma is not likely to be a very good physician.

IMMUNITY

Immunity is a slate of heightened resistance or accelerated re¬ activity toward microorganisms, transplants, or any other nun seif subs I a rices that gain access to the body. An adaptive response, im¬ munity is differentiated from ndnsuscefttibility (in the sense (hat dogs, for instance, arc not susceptible to measles not human beings to canine distemper). Animals may be norisuscepiible to microorganisms because they do not provide a suitable culture medium. Thus baby rats are not susceptible to the rodent malaria organism Plasmodium bergket because they do not provide enough para-aminobenzoic acid Tor tyrghei to grow-. The presen r entry.7 will serve as a memorandum of the conven¬ tional classification of ivnnnintly. It is said to be actively acquired when it has been aroused by an animals own exposure to an im¬ munity-provoking stimulus. This is how most people acquire im¬ munity to measles and other infectious diseases, and this is the kind ofi in rn unity generated by a vaccine Immunity is/wujitif/jtflcquired when it arises secondhand: A newborn child is passively imIJ>3

IMMUNITY

mu m zed by exposure to a maternal antibody transferred through the placenta or yolk sac or in the first milk, the colostrum, that a child receives from the breast. Alternatively, a vicarious immu¬ nity is conferred when blood serum from an immune subject is injected into a patient. In professional parlance immunity is further subdivided into humoral immunity and cell-mediated immunity (CMJ), Hu¬ moral immunity is that which is mediated through the action of a soluble antibody. The cells that are responsible forCMI arc blood leucocytes, especially lymphocytes, An Operational distinction is that humoral immunity can be passively transferred by blood scrum, whereas cell-mediated immunity cannot be transferred byserum but requires transfer of cells, This is a feat not normally possible in real life; to avoid rejection of the transferred cells as foreign grafts, donor and recipient must be related in each other as closely as identical twins are. The barrier set up by the allograft reaction could of course be circumvented if CM I could regularly be transferred by means of a cell-free extract of leucocytes, a pro¬ cedure which has been attempted with some success in human beings using the leucocyte extract named "transfer factor.” The way it works is still unknown. The (fur immunology) characteristically infelicitous term “irnmu nologit tolerance” is used to denote an immunologieally spe¬ cific state of nonreactivity toward a substance that would nor¬ mally have been antigenic. The condition occurs naturally in dizygotic twins and those animals usually cattle and sometimes human beings in which the possession of a common placenta triakes it possible for the twins mutually to transfuse each other with hlood before birth. After birth such twins are found to be chimeras who can accept skin grafts and the like from each other, as sibs normally cannot. The mechanism of tolerance is not yet fully understood. Animals as a rule are tolerant of their own bodily constituents, and ihcir failure to institute or to maintain tolerance is a cause of autoimmune disease. The immunologic response system, we have explained, is ac¬ tuated by the intrusion into the body of tionself substances, Some¬ times it even comes about that the native constituents of the body behave as nonself substances. These may become antigenic in sev-

—

—

154

IMMUNITY

era! ways: some exogenous substance may bind to Lhe constituents of the cjtrl I and thus make them Iti effect foreign (which happens when inrius i rial chemicals such us diniiroch loroben zone or picrv] chloride attach tbCmselves tn the skin and so give rise to allergic dermatitis): a second possibility is that a viral infection may alter a cell const i t u t tonally in such a way that il acquires antigenic properties distinct from and in addition to any enjoyed by the virus itself; still another possibility is dial a mutation may occur' in a clone of lymphocytes and confer a new reactivity upon them one Which they would not otherwise have possessed and which, being random in origin, might by mischance confer rcaetivily against a native ingredient of the body, Autoimmune disease or react ivity may arise also iti a fourth arid entirely distinct kind of way. As a general rule, autoimmu¬ nity is rare because, it is believed, the body acquires immunologic tolerance to its own constituents nr its own secretory products, This tolerance can arise only When the immunologic response sys¬ tem has been exposed to the bodily const fluent in the course ol development, so that the body has had an opportunity to become innnunologicaily Cognizant of it. Some bodily constituents, how ever, may be so sequestered or may arise so late in development that this tulerai tce-coi i foil ing process has no opportunity to occur, Spermatozoa ai’C an example, and so tire some constituents of the lens of the eye, which is non vascular, b is well known that an EULloirninune reaction may be artificially provoked by the inject ion

—

¬

of spermatozoa and ol lens protein. Alternatively, an injury may liberate into the bloodstream win a l would Otherwise have been a sequestered substance. Hnshimoto’s disease (autoimmune thyroiditis) seems to arise as a result of physical or other injury to the thyroid gland and this process (which as explained LEI the discussion of positive feedback is sclfaccrbatiog for antithyroid antibodies) causes more damage to the thyroid and arouses still further autoimmunity. In fact, there may be an autoimmune element in many diseases ih;it Eire accompa¬ nied by injury to bodily organs. Diseases that are suspected or known Lo be autoimmune in origin include myasthenia gravis, si paralysis which resembles that provoked by curare; multiple scle¬ rosis, a progressive paralysis of stealthy origin: and cerium other debilitating neurological disorders such ;LS SSHE (subacute

—

155

I MM [ : NO I .Of; It t

5UR.VEtLJ.AN6E

sclerosing panencephalnmydilis}. Ulcerative colitis, sympathetic ophthalmia; and rheumatoid arthritis arc also categorized as aiir lo immune

diseases.

Because of its self-acerbating character, autoimmune disease is turns upon the use of particularly difficult to manage. imm lihostipprcssivc agents or oT procedures dtrsigued to ancnnpt to interrupt a vicious cycle (For example, washing blood corpus¬

Treatment

cles free of the plasma in which they are suspended and reinject* mg them suspended in a bland plasma substimte), 'J’he special vulnerability of the nervous system to autoimmune disease must surely be due to normal set} nest rat ion of its constitu¬ ents from centers of immunologic response.

IM M UNO LOGI G S U R V LI LL A N C L

A notion that embodies a proposed teleology of the allograft re¬ immunologic surveillance attempts a rationale of the im¬ munologic process that normally prohibits transplantation of organs and tissues from one individual to another. The argument is (hut the rejection of aliogralls is a tiresome by-product ol the exisicncc of a body-wide monitoring system, of which the primary purpose is to identify and cause the rejection of malignant vari¬ ants of normal tissue cells nf incipient malignant growths! in fact. This attractive, plausible, and widely accepted hypothesis was first propounded by Lewis Thomas and developed by Maclarlane Burnet; (hr; will lo believe if to be true has always been stronger than (he evidence m its favor. Its acceptance is of course closely related to ihc immunologic theory of natural defense against cancer. Pathologists give widespread credence to the 1 bosis that incipient cancers arc far more numerous than those that even¬ tually graduate lo become a clinical threat; tire growths that do nut progress, it is argued, must have been suppressed by some normal mechanism of surveillance against cancer. The hypothesis is certainly not true in the rather naive form in which many of us at first accepted it a form based upon the supposition that incipient tumors are eliminated by an immuno¬ logic process almost exactly akin lo that which brings aboul the rejection of pi Ingrafts, This may only mean dial a cell Other than action,

—

1SH

IMim IIJUAIJ 1\

the peripheral blond lyrijphocyte is the piineiptd agent of surveil¬ lance: an altmiiiiivt possibility is the complicity of (lit: so-called natural killer cell, The hypothesis must stand or fall with (hr imiTiu nologic interpretation of resistance to tumors: if that hvpmhcsis is false, then the idea of immunologic surveillance must surety be mistaken. Right or wrong, the idea has fulfilled (he principal function of a sc: ICIU if ic theory: u has led tn observations and experiments that would not otherwise have been performed, In this ease subslant tally enlarging our overall understanding of cancer.

INDIVIDUALITY A pseudbprobterti invented by nature-philosophers to give biol¬ ogy an air of profundity, the "problem" of individuality arose out ot the following circumstances- Several groups, of which represen¬ tative members are solitary and sessile and which accordingly have considerable powers of regeneration and of asexual repro¬ duction, exist in colonial as well as solitary forms. Examples are corals and saJpas and pelagic organisms such as PhysaUa, the Por¬ tuguese man-of-war, and LLS relatives. These colonics arc, so to speak, biological polymers, of which the Structural unit Of mono¬ mer corres ponds in structure to the solitary sessile form character¬ istic of the group. In corals this is an individual hydroid or polyp, and in salpas it is a sessile individual tunicate. The so-called indi¬ viduality problem is whether these colonies (which are highly in¬ tegrated structures with a good deal of division of labor among the individual parts) should be regarded as colonies nr as individ¬

ual organisms, When w'c authors were students, the [individuality problem was one of the topics upon which we were required to write critical and analytical essays. We were not sophisticated or philosophi¬ cally literate enough at the time to denounce the individuality problem as a fraud a non problem of very little interest, upon the answer to which nothing of import anee turned. For an or¬ ganism such as lyrosor/ui is both an individual mut a colon v com¬ pounded of individuals: there is no ruling that an individual or¬ ganism, properly so called, must consist only of individual cells, In many respects a termite colony is an individual organism a

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157

INFERTILITY AND ITS REMEDIES

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social polymer of which the constituent parts correspond morphologically to the individual solitary forms. Nature-philosophers had an unhappy propensity to invent problems. Another pseudoprublem was the question of whether connective-tissue fibers are alive, as cells are alive, or are to be dismissed as dead. The manufacture of all such problems is en¬ tirely supererogatory. Biology' is already difficult enough. A gen¬ uine problem having to do with individuality is discussed in the

sort of

entry on TRANSPLANTATION.

INFERTILITY AND ITS REMEDIES Infertility in marriage is much more widespread than is com¬ monly thought: reliable estimates put its frequency in the United Kingdom today ai about 10 percent, for some causes of infertility manipulative remedies have been devised that may involve fertil¬ ization of the female egg cel! in vitro (literally, "in glass" in ef¬ fect, in a suitable vessel outside the body) before implantation into the mother's womb. Female infertility sometimes results from an obstruction or other abnormality that prevents an egg cell from passing down the oviduct into the uterus, in the wall of which, after fertilization, it normally becomes implanted. A rem¬ edy i hat has been recently introduced is the in vitro fertilization of the oocyte with the husband's sperm. Reimplantation of the fertilized egg into the uterus may be followed by a normal preg¬ nancy and delivery. Babies raised by this procedure have been referred to as icsttube babies a highly injudicious misnomer in which a taste for alliteration has got the belter of common sense. These are not babies in any ordinary use of the term: they are embryos at this stage lacking brain, eyes, ears, or nervous system. To describe them as human beings because they derive from and turn into human beings is tin a par with describing an aeorn as an oak. Embryos, babies, and human beings are different in fact and ac¬ cordingly in name: to use for one the name appropriate to one of the others is a widespread cause of mischief and misunderstand¬ ing. In order to improve the chances of successful fertilization in

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I5H

INFERTILITY

AND ITS REMEDIES

vitro the mother may be induced by hormone treat men l to "sitperovuiate” that is lo say, to produce several egg cells at the same time. Inasmuch as only one of these \sil I be fertilized and used lor Uterine implantation, the remainder, if not discarded, tin: sometimes used for the study nf lunuar development for exam¬ ple, stimulating a fertilized egg cell into forming a clone. The dis¬ carding of unused egg cells has been likened to murder by oppo¬ nents nf the whole procedure, on the grounds that the object being experimented on is a living human being, [’lie general public, however, supported by a sturdily Johnsonian common sense, regards the process as a humane and gratifying remedy, of which the dlbct is to bring into the world a child enjoying one of the most impressive advantages a newborn babe can have: mat of being very dearly wanted. When (he cause of infertility is some deficiency or inadequacy on the part of I he male, diifcrcnt expedients may be used, espe¬ cially those involving the use of A I (artificial insemination), a procedure which the media do their best lo represent as appetis¬ ing] y salacious in character. When a male partner can produce ostensibly normal sperm but lor one reason or another, whether psychological or physical, can¬ not introduce them into the vagina, artificial insemination by the husband s sperm (AIH) may well be resorted to. If things go well. the child so conceived is in every sense us parents’ child. This procedure is not normally objected to on moralistic grounds, pre¬ sumably because the entire operation is too clinical in characier to amuse prurient interest, On the other hand, there has been strong opposition to AID. artificial insemination which uses the sperm of a voluntary donor. The primary objection has been that the parental relationship under these circumstances is not genuine and that the child is no more than a step-child. It has been objected, too, that if AID were to become widely prevalent, we should populate the world with half-brothers and half-sisters and (hereby risk inadvert cm inb teed i tig. with the ensuing genetic dnninge. The likelihood of such a misadventure is negligibly small, and we are not impressed by the idea that artificial insemination is likely to Supplant the natural procreative processes and parental feelings that have sufficed hitherto. As to AID's being 'unnatu-

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i.'jy

INSTINCT

ral/3 we regard the children horn in this way as adopted children, with ihe advantage over ordinary adopted children of having grown within and having been delivered by the adoptive mother, who may accordingly be expected to feel particularly close to

them. Ali i he procedures we have discussed are special remedies for special Ills: ordinary To lb can be pleased and reassured by the thought that such antidotes arc now available to them unless indeed they are withheld out of religious bigotry or because t>r the strong but usually unfocused resentment ihat not very bright members of the lady feel at the supposed usurpation and diminishment of human prerogatives by modern science. We find this a ridiculous view, for all the procedures we have described encour¬ age a restoration rather than a withdrawal ol I'm [nan preroga¬

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tives.

INSTINCT

Instinct is a concept more easily described, explained, and ex¬ emplified than made the subject of a Torn ml definition. For the benefit of those insecure people who fed that no discourse is pos¬ sible unless words are defined a counsel of despair nullified by the fact that biologists have discussed instincts for many years wit houl attempting a formal definition the term '‘instinct is almost invariably used to describe not a single action, but a func¬ tionally connected train of performances having what ordinary people describe as a purpose (for example, a newborn marsupial's spectacularly precarious climb from womb io pouch). Perhaps the first property that comes to mind When the term "instinctive” is used is the property of being unlearned of being ostensibly the acting ouL of an innate or an inherited scenario. It should be added, however, that some performances described as wholly instinctive in reality depend, as bird song dues, on environmental cues. Automatism is another characteristic tradi¬ tionally associated with instinctive behavior, especially its per¬ formance even when it is functionally inappropriate and coniraadaptive, and it is often combined with a certain inflexibility thaL prohibits modifications to suit special circumstances,

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160

INSTINCT

As a figure of speech, performances are so me limes described as instinctive when all thai is intended is reference to the functional aptitude of a performance combined with its prompt and effec¬ tive execution. Thus accomplished drivers sometimes describe their driving as pretty much “instinctive/1 a usage that illustrates very well the truth oT Alfred North Whitehead's wise judgment in his Introduction to Mathematics (London, 1911, p. hi): ‘ [t is a pro¬ foundly erroneous truism, repeated by all copy bonks, and by emi¬ nent people when they arc making speeches, (hat we should culti¬ vate the habit of thinking what we are doing. The precise opposite is the ease. Civilization advances by extending the num¬ ber of important operations which we can perform without think¬ ing about them.” We regard this as a profound observation which most people will be able to bear out from their owrn experience. Learning a new repertoire of neuromuscular performances such as driving a car or skiing is precisely learning not to be obliged to think about them. It is learning to react promptly and appropri¬ ately to each stimulus as it presents itself. Our behavior must be quasi -instinct rial, for these are performances in which ratiocina¬ tion has no part, though judgment it is to be hoped will have been exercised by insuring against the breakage of one’s limbs that so often accompanies skiing and other people’s m when driving a car or, as English people absurdly say, "motor¬ ing.” The neuromuscular scenarios of instinctual performances in the social behavior of insects and mating behavior of animals are extraordinarily complex and at present we have no inkling of how they are programmed. Still more extraordinary is ihc situation in which a behavioral program is merely latent, although some ap¬ propriate stimulus may call it forth, Such is the case, for example, among chickens, for cocks may be caused to display the entire repertoire of female parental care if they receive injections of fe¬ male sex hormones. The more one thinks about this circumstance, Lhe less easily explicable it seems to become. Biology has no greater triumph to look forward to than a solution of the problem of how a program ofinstinctual behavior is genetically stored and epi genetically retrieved. What about plants? To describe any activity of a plant (such as the astonishing performance of an insectivorous plant like

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J61

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INTERFERON

Venus’s- flytrap) as ‘"instinctual” violates natural usage, yet the word would have been used if plants had nerves and muscles. In spite of the fact that a plant’s “psychism,” in the words of Teil¬ hard de Chardin, is so “diffuse,” there is no reason why biologists should regard the possession of a neuromuscular system or a psy¬ che as a necessary condition for an organism’s behavior to be de¬ scribed as instinctual. All that need be said is that plants have ef¬ fectors of their own and sometimes perform in ways which it is not fanciful and might even be instructive and liberating to de¬ scribe as instinctual. Plant behavior is a subject that needs to be more fully explored-

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INTERFERON

It is well known that the infection of a cell by one virus makes it relatively refractory to infection by a second virus. The chemical agent shown by Alick Isaacs and Jean Liudcnmann in 1957 to be responsible Tor this phenomenon of viral interference is known as “interferon," or, more properly, “the interferons,” Although inter¬ feron is not a single homogeneous substance, interferons have a variety of natural functions and clinical uses in local or systemicvirus infections, and for reasons still unknown arc useful in the treatment of certain forms of cancer even if the cancer is not or is not known to be of viral origin. The full capabilities of the interferons arc not yet known, for they are species specific and work best in members of the species in which they' themselves were formed. For this reason interferons are in chronically short supply. Only when adequate amounts be¬ come available quantities on the order of kilograms can their full potentialities be investigated on an adequate scale. ft is helpful, though, that interferons can be produced by other than viruses— by, for example, a variety of so-called interferon in¬ ducers, among them a number of the double-stranded synthetic polynucleotides. The production of interferon has been attempted in the following ways. First, a human leucocyte concentrate or cultured human cells, sometimes cancerous cells, can be treated with viruses or interferon inducers. The yields, however, are ade¬ quate only for small-scale laboratory experimentation. A second

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ttili

INVLR f KHK.VI A

procedure is to introduce interferon genes into microorganisms by the techniques ofbfoengipeering, and theiSt endure me microorga¬ nisms on EI massive scale, The third method, which shims before

...

us like the Holy Grail (and like the Holy Grail seems sometimes to recede as we approach it), is organic synthesis a formidable task

indeed: although natural interferon molecules have carbohydrate attachments, the working moiety of the molecule is thought to be a protein with a molecular weight of about 4,tXMJ. But those production problems are soluble and will be solved; they ate a necessary condition for fit lure progress. When sufficient quantities are available to expose interferon ton!] (he (ests labora¬ tory scientists imd clinicians have in mind for it, we are in for sonic very pleasant surprises- Tn out judgment interferon may well conic 10 rank as one of t lie truly impressive biomedical discoveries of the

twentieth century.

INVFRTFJ1RATA

A word that has the ring of a taxon, “invertebrata” is in reality merely a description ol a miscellany of animals united only by the property of not possessing a backbone. Clearly the lack of a char’ acteristic will not in itsdtf carry taxonomic weight i for if it did protozoa, also lacking backbones, would be rated invertebrates. And so would plants, Convention therefore restricts the use of the term to metazoa, (0 many-eelled animals. The groups that constitute the invertebrates are distinguish’ able into two major lines of evolution ary descent, the distinction being based partly on erribrvomc development and partly on the fundamentals ol adult structure. Thus the annelids, tbe arthro¬ pods, and for develop men t al reasons the mollusca form one such line; the annelids and arthropods possess a vent rally placed ner¬ vous system and a dorsal heart. To this lineage wc may add other groups almost certainly derived from it by ncoieny, such as the round worms (nema Lodes) and the so-called Wheel ;mi male tiles, the readers, Vertebrate animals eharact cri&t ictiHy have a dorsal ly placed nervous system and a ventral heart. Several invertebrate groups are united by lying on nr dose to die major line of descent that

m

IKKJTABILITY

leads toward the chordatcs- These poor relations arc the Kchuidÿ derms (sea urchins, starfish, and sea cucumbers) and the group of which the principal member is am phi ox us: iri addition, there are a few minor groups whose claims fur admission to the chordate line of descent are in some ways less convincing -the groups of which t tic representative members are arrowworms {Chactognatha)t the Phanmida, and moss animals (JEtfoprwta),

IRRITABILITY

A term that almost invariably figures in fists of differences be¬ tween living and inanimate matter, ‘‘irritability” means no more than reactivity or responsiveness to changes in t lie environment. Certainly the complete lack of any sue it responsiveness is often construed as evidence of Lifelessncss. "Irritability" has, however, a more particular meaning: Johannes Mi.illcr, the great German physiologist (f 801 -]&r>8), formulated a Law of Specific irritability, sometimes called his Law of Specific Nervous Energy, wlneli we describe in the entry Oil SENSE Okti.AM-S,

164

!KJNG

GRAB More than one crabJ ike crcaiurc is refarreKlrr). We cannot gainsay that drift occurs, LULL the magnitude -f J f its Contribution to evolutionary change is still a matter of debate Adherents of (he notion attach particular importance to drift as ii occurs in small populations. A second agency that may change gene frequencies systemati¬ cally is tile pressure of one current mutation the repeated SLIIV solution, for example, ol mutant allele A' for gene A. However; mutation is so infrequent an event that Darwinists do not look upon mutation pressure as an important agency in evolution. By far the most significant agency is natural selection, Darwin's own enduring contribution to biology, which lias tint diminished in profession a] esteem even though laymen and amateurs often disapprove of the notion. Among the misconceptions about neo- Darwinism none is more widely prevalent than the one which presents it as a deelaraiion that what Nature sheets is mutations or more correctly, mutant genes or mutant -organisms. Tins is a travesty of neb-Darwimsrn, and we take the opportunity to reaffirm our proposition that mu¬ tations do nut arise m response tceaJT'Ot'ganism’s needs, nor do they, except by accident, gratify (hem. Candida! lire for evolution is provided by tin: virtually infinite range of variant's thrown up by thy genetic recombination that is made possible by genetic segre¬ gation, tile random reunion ol gametes in the sexual process, and by crossing over. This prodigious combinatorial variety, with the rccojnbj titu ional elements ftitt her enriched from time to time by mrnaiion, proffers to natural selection a repertoire comprising trillions of candidates of possible organisms any one ol' which might contribute significantly to a solution of the problem of re¬ maining alive in a predominantly hostile environment. Shch is tlm uco- Darwinian theory of evolution by natural se¬ lection. Darwinism Itself has faults, of course: ii cannot be wholly acquitted of (lie charge of explanatory glib ness and the reproach that it does not account very convincingly for evolutionary progression —that is, for the adoption of solutions that are more complicated than called for by the bare requirements of subsis¬ tence and reproductive solvency. The objection most frequently made, however, is one Which cannot be sustained: that it is incon¬ ceivable that evolutionary adaptations with all their finesse and re¬ finement of detail could possibly have come about by such a

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198

JiEQTENY

mechanism. Flie “irtcopceivabiltty” cbm plaint is a criticism of Qiii twelves rather than of neo-Darwinism. \\rer cannot but remem¬ ber that the distinguished English respirhtbry physiologist John Scott Haldanedeclared it “inconceivable" that thepe should exist a chemical compound having exactly the properties dcoxyribonucleic acid is now known tO possess, as an digram of hcretiiiy, a system of instruction fqr tin: execution of development, fleibrDarwinism has its own faults, of course. Like Darwinism. it has a measure of glibness. Moreover, it is difficult k> think of any experiment or set ol observations that could possibly falsify it: one such tesl would b(S to establish a heritable difference by artifi¬ cial selection among a population of highly inbred, indeed homo¬ zygous, mice. Thus if Samuel Butler and William McDougall had been right in their surmises about tile heriiabilny ol behavior, be completely undermined bv improving neo-Darwinism learning ability by selection of inbred mice throughput an experi¬ ment lasting many generations on l he same diet, Even if any biol¬ ogist were willing to undertake such ait experiment, no grant giving body knmvn to sdencc would be willing to fund it.

NEOTENT The relative rates of development of she several parts of the body, including the gonads, are not invariant. One of the most in¬ teresting (and from an evolutionary from! of view one of the most important) departures from a set tempo and order of differentia¬ tion is that whereby organisms become sexually mature at a rela¬ tively juvenile stage. What is in effect an adult therefore retains juvenile, even larval, characteristics in adult life. The general term for the phenomenon, coined by Gavin do Beer, is pcdonuirp hosts, Neoteny, the authenticity of which cannot be questioned, is best exemplified by die Mexican axolotl, the larval form of an American salamander of the genus Ambyxtoina inter which it may be induced to metamorphose. Walter Garstang was one of the first to derive the higher ehordates from the “tadpole” larvae of sea squirts by neolcny. The inherent plausibility of the theory is witnessed by the fact that one entire class of the sea squirt phy-

tyy

NERVE GASES

lum, the so-called 1,/trvacea, is composed of clearly neolcmms sea

squirt larvae. Human beings, it is thought, owe some of their characteristics to being neotenous in relation to the great apes, Ludwig Bulk in I92fi introduced the1 term fetalizatim to describe the changes that caused human beings to retain some of the characteristics of fetal apes: the relatively enormous brain, the position of the foramen magnum and the rectangular set of the skull in rclaiiun to the backbone, the hairless body, (he light color of the skin, and cer¬ tain other characteristics. With his usual inventiveness, Aldous I luxlcy in After Many a Summer imagined a state of affairs in which extreme prolongation of life made it possible for a human being to metamorphose into an adult ape. Considered as an evolutionary stratagem, neoleny provides for relatively rapid and radical evolutionary trails form a lion, provid¬ ing what A. C, Hardy referred to as "an escape from specializa¬

tion.”

NERVE GASES

A nerve gas is a volatile liquid, often an orgartophosphorus compound, and the vapor issuing from it effectively paralyzes its victims by its action as an anticholinesterase. The nerve gases thought most highly of by those who have a mind to use them are colorless and non irritant and therefore extremely insidious in their action. They have some application as pesticides.

NERVE IMPULSES A nerve is essentially a bundle of nerve libers proceeding in the same direction. As a rule, it connects the central nervous system, brain, spinal column, and so forth with motor end organs and, conversely, connects sensory organs with (he central nervous sys¬ tem, Such bundles of fibers have a delicate connective- tissue framework and are supplied by blood vessels but not by lymphat¬ ics. A nerve within the central nervous system that connects one pari of it with another is referred to as a tract: an example is the

200

XI.1C I

K, to

ACIDS

Iran, which conveys nerve im¬ “pyramidal’ or pulses from ihc OdPÿbral cortex down the spinal cord. Peripheral nerves may ire motor or sensory nr mixed, From the way in which the eye arise.': in development, it is clear that the socalled optic nerve is not really a nerve in the sense in which the sciatic nerve may be so described; it is a brain trace The cell hf uhes oT the sensory neurones that run in tit is tract lie in the ret¬

ina itself.

Nervous communication is transacted by nerve impulses. A nerve impulse is a propagated change of state in the membrane of the nerve fiber; nothing material passes down the length of Ehe filter, any more than it dttes m a line of dominoes so arranged thai knocking one over knocks down its neighbor and so on. This too is a propagated change of state; what moves is a signup riot a mate¬ rial substance, A nerve fiber can conduct impulses in either di¬ rection. The interface between two neurones, the synapse, polarizes the impulse, which can cross the synapse one way only. Signals in the nervous system work on the I'M {frequency modulation) as opposed to the AM (amplitude modulation) system because trains of nerve impulses tidier one from another in their frequency only; [be amplitude is fixed anti does not die away as the distance from the point of stimulation increases. However, if by a narcosis or some equivalent means the amplitude is caused to drop over some stretch of nerve, it picks up again to its original value when ilu: signal has passed the affected stretch. This is evidence that nerve impulse is self-energised, that is, powered by the nerve it¬ self. The nerve impulse has been described by otic oT its principal students as “the universal currency oT LIIC nervous system ’’ In¬ deed, tin: fact that most of the business of the nervous system in¬ cluding the brain is transacted by electrical signals is one of the respects in which brain and nervous system are computerlike.

NUCLILfC AC1L>S

Proteins, carbohydrates, and fats have a huge variety of struc¬ tural and metabolic functions to perform in the body, but the functions ol nucleic acids are comparatively simple:, they arc 1 he 201

NUCLEIC ACAIJK

vectors of}jifbrtiiÿ|]oii Icjt development and heredity. Thus its nu¬ cleic acid moiety is that part of the chromosome which conveys the hereditary message, and it is another nucleic acid that relays (Ills message to the synthetic math merry of the cell, causing a pro¬ tein to be assembled in a particular way, with its constituent amino acids lined up in a specific ordcr. A nucleic acid is a huge elongated molecule of a chemically re¬ petitive (polymeric) structure.of which the backbone is Formed by Linkages between phosphate and 5-carbph sugar molecules. These are one or the other of two kinds of molecules dial give their names to ihc main categories of nucleic acid: ribose in ribonucleic acid (RNA) and iUwtyjibost in deoj$iribonud eie acid (DNA). The nucleic acid of (he chromosomes is DNA, which is found also out¬ side the nucleus in, for example, mitochondria. Attached to the phosphate backbone art nitrogen -containing organic basts that are purines or pyrimidines. The tectonic miii of a nucleic acid the monomer of which the polymer is compounded is a tiuckotidt, composed of phosphate, sugar molecule, and organic base; it Es the order of the organic bases down the length of the molecule that encodes the genetic in forma tioti or genetic nurssage that pauses from one generation to ihe next. In (he synthesis of a pro¬ tein, which requires the assembly of constituent amino acids in a particular order, the ribonucleic acids (which are of different functional species) act as go-betweens, hirst, the specific order of nucleotides in the DNA molecule is mapped onto a strand of mes¬ senger RNA. Upon the structural basis of a minute cytoplasmic panicle known as a ribosome, this messenger RNA marshals yet another (soluble) Species of RNA known as transfer RNA, each molecule attached to a specific amino acid. By this procedure in¬ formation contained in the original DNA molecule is mapped into the structure ol'a protein. By convention, the transaction be¬ tween DNA and RNA is known as transcription, while the RNA is said to be translated into the structure of protein. It is widely believed that ihe researches which uncovered the structure of nucleic acids, explained how they fulfill a genetic purpose, and demonstrated how they convey information in cel¬ lular metabolism, are among the most brilliant and illuminating scientific advances of the twentieth century. With this interpreta¬ tion we concur. Jt was a long business, though, for when nucleic

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202

—

NUCLEIC ACIDS

acids were firsE recognized as chemical entities. the methods of extraction were so violent, often involving heating in an alkali or i he like, that ihe crystalline structure bf the nucleic acid was finite destroyed. The researches that finally established (he complicity of nucleic acids in genetic information transfer arc summarized iii (he entry un MOLECULAR BIOLOG V, Ihe initiative Was in some sense a conceptual one. Only when the gene was conceived as a Jdtssogf did ilierc arise a special incentive to associate these gene messages with (be particular crystalline structure of a macro* molecule such as nucleic add. ft is the linear differentiation of the molecule that provides Idr information transfer, but replication is made possible by the fact that the hcheai Molecule is double stranded, the two strands being com [dement ary in such a way that cither half may be made the basis from which a complemen¬ tary half can be assembled,

203

ORDER

IN BIOLOGY

If vvc were to be confronted with an unfamiliar obiject, whether of microscopic si see or large enough to sec, then ask if it were a liv¬ ing organism or the remains of one, we should almost certainly hasc our answer on the degree and kind of order in the object lacing inspected. For order is everywhere evident; in an Organism's definite shape and distinctive symmetries; iii the crystalline tidi¬ ness of chromosomes, viruses, and many of the constituents of cells; in the giant polymeric molecules that are so abundant a con¬ stituent pf living organisms; and in the products of the activity of organisms such as honeycombs, spiderwebs, and the various kinds oT ‘‘houses” Or nests whirh organisms make for themselves. Order

permeates biology' through and through. A system displays order when its constituent parts are not ran¬ domly assembled but manifest only one or a few of the possible configurations of iheir elements in space and lime. So considered, any given configuration may be thought of as an improbable unc, (he degree of improbability being clearly related to the number of possible configurations. This; reflection gives intuitively a sense of the connection beLween order, disorder, and probability. No gen¬ eralization in physical science is more firmly established than that whirh declares that the direction of flow of events in the universe is always from less probable to more probable always, that LS, to¬ ward randomness and "mixed-tipncss”- toward the t:(popart it ion in the universe of that which began by being separated and nnct|ually divided. With i his, as Lord Kelvin was first to discern, goes a progressive loss of the ability io use the heal in the universe for performance of mechanical work, Although the total amount of heat energy in the universe remains constant, it is “irrevocably lost to man” and therefore “wasted," though ILOL '‘aniuhdaftd/' in thermodynamic transactions for the performance of mechanical work by heal

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2SD4

OMU It IN BIOLOGY

upon tlit; existence of inequalities in the system that arc pro¬ gressively done away with in a vast and universal leveling. In Ludwig Bolzmann’s formulation the relationship between emropy Sand order is given by the expression S = k log W, where k is the universal Bolzmann constant and W the probability of the prevailing configuration of the system. Where the probability of a rests

—

given coil figuration is unity, there is no possibility of alternative configurations. Under the circumstances, die entropy of the sys¬ 0). Such is the tem is of course zero (remembering that log 1 case of a perfectly pure crystal at 011 K (absolute zero), where heat motion is at a standstill. 1’he relationship between information and order is made intui¬ tively clear by the observation that information embodies, ex¬ presses, and often specifics order, Kor nearly all information is im¬ parled in the form of a linear configuration of symbols, the specificity of which depends upon the way in which these symbols are ordered, Consider, lor example, the anagrams time, item, mite, and emit four different words that are so by reason of the order of the alphabetic symbols of which they are composed. An ordi¬ nary message like that contained in a telegram would cease to convey information if its elements were randomly mixed as in telegrams they sometimes are. Clearly, information and disorder arc antithetical, and information accordingly can be defined and quantitatively measured as negative entropy. A chromosome or ati architect's drawing is said to cum a in information because either may be conceived as a scheme of instructions for imposing or generating order. Erwin Schrodinger (l&87-19fil} was one of the early physicists who made significant contributions to biology. In his illuminating little essay What Is Life? (Cambridge, 1944) Schrodinger was the first to propose that the phenomena of he¬ redity turn upon a coded message transmitted from one generation to the next, the message being embodied in a chromosome, con¬ sidered as an aperiodic crystal, in which the structure is such as to be relatively insulated from the disordering effects oT heat motion. See the entry on NUCLEIC ACIDS. Do living things circumvent or flout the Second Law of Ther¬ modynamics? Rudolf Clausius' famous dictum that entropy of a closed system tends always to a maximum value i.s as true of living organisms as it is of the physical world, Still, it is very natural that

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205

ORDKR IN BIOI.OCY

the pervasiveness and ubiquity of order in biological systems should have created the impression that evasion of the Second Law is a distinctive and crucially important characteristic of liv¬ ing things. This viewpoint is mistaken, however, and grows out of failure to realize that the law applies only to closed systems- systerns lit which there is no external traflic in matter or energy. In a closed system the increase of order in one place is matched by an increase of disorder elsewhere as it is. for example, in a domestic refrigerator, the cooling of which must be paid for by the heat generated in the pumps ihm compress the refrigerant gas and cir¬ culate it so that it can “excrete” its excess heat into the environ¬ ment. A living organism, said Schmdiuger, “drinks orderliness from the environment”; he was referring to the continual degra¬ dation of small molecules in die course of metabolism, which pays the thermodynamic bill for the generation of complexity, nor¬ mally of a higher order. Nevertheless, it is fair to say, as Aharon Katchalsky more than once has; “Life is a constant struggle against the tendency to produce entropy. Since there is no escap¬ ing the entropic doom imposed under die second law or thermo¬ dynamics, living organisms choose the lessor evil they produce entropy at a minimal rate by maintaining a steady stale," The production of a symmetrical molecule, or of a structure such as a spiderweb with its symmetrical features, leads to a greater loss of entropy than the production of an asymmetrical structure, The thermodynamic cost of symmetry, however, is minutely small. The entropy loss involved in spinning a spider¬ web would not, because of the symmetry, be significantly more than the loss already associated with the burning of sugar mole¬ cules to compensate for tile physical exertion of spinning (unless, of course, the spider did more work to spin a symmetrical web than to spin an untidy or haphazard otic). Robin Valentine once called our attention to a striking exam¬ ple of the degree to which changes oT order arc entirely inappaient. He cites the formation of tobacco mosaic virus (TMV) from its subunits. TMV is a highly ordered crystal, and its forma¬ tion must lead to a loss of entropy; entropy elsewhere must there¬ fore increase. So we should expect a rise in temperature of the sol¬ vent -but in fact the solvent cools. This, we were told, is because the surfaces of the virus subunits are hydrophobic and therefore

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206

ORHKRS OF M.UiM Il'DI in the water by which they are Surrounded- Wheft ihc units aggregate, their hydrophobic surfaces arc in turned, causing the solvent to become mim: disorganized; this ou (Weighs the order created in the vims. In this case, then, the Second Law actually favors the creation of a well -ordered virus, James Clerk Maxwell (l83$-.|p7l) envisaged a situation in which the Second Law of Thermodynamics was circumvented by a being with intelligence and a very high degree of perceptive ness. Let us suppose, said Maxwell, that a vessel is divided into two portions A and B by a partition in which there is a small hole. An observer able to see the individual molecules opens and closes this hole so as to allow the swifter molecules to pass front A to 11 and the slower ones to pass from B to A. He will ihtls Without ex pen Hit tirtr of work raise the temperature of B and lower that of A. in contradici ion to the Second Law of Thermodynamics. Maxwell’s “demon,” as he came to be called, highlights tint notion that in¬ formation is negative eturopy.

induce order

ORDLRS OF MAGNITUDE

In biology very small quantities are come upon more often than very large tines, and the accompanying table will serve as a memorandum of the le mi inn logy used for orders of magnitude. Order of

Name of fraction

Proportion of a inetcr

Meter

Unity

Decimeter

'Tenth

Gem i meter

Hundred)

Millimeter

Thousandth Millionth

Micrometer

Nanometer Picomder

Billionth Tritlinmh

Tiiagii i i uclt'

(power of 1U) 0 -I

—2 -3

-a

-[j

-12

We need tfi remember lot) that a desi gnat ion such as IQ - 1 stands for l /I O1, that is, pne thousandth, and thÿf( by convention I0lh= I. A corresponding terminology applies in gravimetry, in which the unit is one gram: thus milligram, microgram (fi), n-mogram.

ORIGIN OF LIFE

and so on. In volumciry, the unit of volume is one tiler: one milli¬ liter is approximately one cubic centimeter and one microliter is about one cubic millimeter. Latin prefixes are used for quantities less (ban unity and Creek prefixes for quantities greater than unity; thus (/mi-, hecto kilo,and mega- signify the multiples 10, 100, 1,000, and 1,000,000. In professional writing extremely large or extremely small figures are almost always represented as powers of ten, positive or negative as the case may be. The orders of magnitude of the quantities above, then, are (+) t, 2, 3, and 0 respectively.

ORIGIN OF LIFE

Scientists who believe neither in miracles nor in spontaneous generation have naturally fell themselves under obligation to give an account of how living systems may have arisen under the con¬ ditions prevailing on the surface of a primeval earth from inor¬ ganic precursors, the prior existence of which was taken compla¬ cently for granted. So probing the origin of life has grown into a minor research industry which some practitioners and lookers-on regard as important, exciting, and absorbing. It is only fair to say that there arc others who regard the whole subject as a painful bore. They are in good company: from a letter to Sir Joseph Hooker, we take it that Charles Darwin was one of them, and though he does not explicitly say so, Erwin Chargaffis probably another. Research into the origin of life is not of vita) importance in any sense that the advancement of learning depends upon its suc¬ cessful completion. Experiments to date show that the exposure of carbon dioxide and water to forty million electron-volt helium ions from a sixty-inch cyclotron may lead to the formation of mi¬ nute quantities of formaldehyde, which would certainly disappear very quickly under the oxidizing conditions that currently prevail on the earth (though not perhaps so rapidly m the reducing atmo¬ sphere Aleksandr Oparin has postulated Tor the primeval carih). In other experiments in which Harold Urey has played an impor¬ tant part, mixtures of water, methane, and ammonia exposed to electric discharges, uhraviolet radiation, and some other sources 20®

OR.NTIHOI.OCY

ofenel*gy may form formaldehyde, hydrogen cyanide, and hy sec¬ ondary reactions teveii amino acids and purines, essential ingredieills of protein and nucleic acid molecules respectively, From time to time ii has been claimed that metebitiliSi contain organic modules such as hydrocarbons and even a to i no acids, but die possibilities of contamination arc so great that these claims have, been greeted with e*t rente caution, Needless to say, these findings represent only a partial solution to the problem and not the more important pa rt, cither. Beyond meter assembly of the raw materials for hiological molecules, an adequate theory must postulate some means by which they can t'ccruil more molecules and enlarge their own substance, a process that will surely turn upon the formation of a membrane and a primitively cell-like structure. The present ex penmen ts dn tin I go very far, but they make one point of considerable philosophical importance: the origin oT lift from in organic precursor substances may be in die very highest degree unlikely, but the phenomenon is not inconceivable. However dim n may be, a first conception of hmv life might have come about is a necessary condition for future progress' without it, there can be none.

ORNITHOLOGY

Part science and part nautral history, ornithology owes its \ re¬ men dons popularity as a science and a scientific recreation to a simple circumstance that is sometimes forgotten when we weigh the eligibility of different kinds of animals for informal study: birds arc day animals where others, jusi as engaging in their Way mice, for instance are creatures of the night. Apart from their visibility (something very much in their favor), the beauty of birds and their tuany appealing habits have won for them a huge fan following that has more than once tempted impatient and illin formed laboratory biologists to dismiss ornithology as so much bird -watching an absurdly unjust judgment dim ignores the fact that ornithology has made a number of profou ndly impor¬ tant Conliibul ions to general biology. Profession a! biologists are not hard put to reel off a list of dt.s-

—

—

—

209

ORN[THO[£ naturaE rights. This is a most questionable argu¬ ment, for who it as conferred upon human beings tire right to bring genetically Crippled children into the world? and how many would insist on standing on their rights to the extent of know¬ ingly doing so? All hough it does not affect the principle of the situation, it is highly relevant to the practical disc nf preventive eugenics that ihe t lire at to human liberty entailed by this eugenic procedure is quantitatively very to i nor. A recessive dis¬ ease with a frequency of, say, one in ten thousand birihx is the victim of a deleterious recessive gene with a frequenev (p ) of about 1/100 in the population. According to the HandjS Weinberg Theorem, where the gene frequency is 1:100 the fre¬ quency of the afflicted homoKygotes, fr, is 1:10,000. and the frequency of the carriers to whom we arc referring, the hetorozygotes, Will be 'Ip = l:o0. The outcome oft his is that ihe Frequency of marriages between earners will he I S3,500 (i/50 X 1/ljO), On the average, therefore, only one in 2,500 particular marriages would then be contraindicated through the carriage of this partic¬ ular gene, and each disappointed partner would in theory have foriy-itine others to choose Irom. These figures, of course, paint too bright a picture because we may be ohliged to grapple with not one but several stich deleteri¬ ous recessive diseases, and partners judged eligible with respect to one recessive disease may conceivably Hunk when other genes are taken into consideration. Moreover, the quotation of frequencies that relate to the popu latiop as a whole is not likely to do much to comfort those who suffer die distress associated with being warned against a marriage which on other grounds had been deemed suitable unless of course the partners, wiih almost intwo

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—

213

PJl.TDOWN SKULL

human equanimity, tail derive an equivalent sat is fat lion from having avoided the risk of bringing a biochemically Crippled child into the world. A caution is necessary. The restoration of victims of PKU to some thing approximating a normal life by the use of diets low in phenylalanine, and the discouragement of marriages between carriers of the offending gene are measures strongly dysgcnic in tendency and would make tin: PKU problem worse in succeeding generations. Their effect is virtually to cancel the work of natural selection in eliminating the PKU genes from the population. The constant reimrodtiction into the population of the olfending genes through mutation is no longer counterbalanced; for it is only through the deaths of those that possess i! that a gene can he reduced in frequency. Under cither of die regimens of contain¬ ment recommended, the bad gene is nm removed from the popu¬ lation and there is noth mg to prevent its frequency from slowly increasing through the recurrent process of mutation.

RILTDQWN SKULL

Between 1908 anti 1912 a number of supposedly human re¬ mains were discovered by Charles Dawson anti several colleagues in a gravel pit ill Pi It down, in Sussex, England. Associated with them were a number of artifacts worked tools of flint and bone, and a number of fossil remains dating the find as early EJaleoccne. These remains were dignified by the specific name Eoanthwpm dawsvni {’‘dawn mail,” Sir Arthur Smith Wtrod ward’s Earliest Englisfi&utn). The finds were unintelligibly anomalous, the braincase being domed and u nmistaknhlv human and (he I never jaw being that of art ape. The anomaly was not resolved until twro British physical anthropologists, with the moral support of a fa¬ mous anatomist, declared the skull to be a fraud: to simulate great age the bones had been steeped in salts of chioiniutii, and to simu¬ late wear the teeth llad been artificially filed down. Later it be¬ came clear that ihe Fossil remains accompanying the skull had been deliberately planicd lo give an air of antiquity to the discov¬ ery. There is no conclusive evidence ined militating anyr one man, al-

—

214

POIKSIS

though suspicion has fathari on all the principals; in t lie d isco vffif.i tifU excluding Pierre Tetlhjond tie Oust'd In, one of DaWsotrs assis¬ tants, Teilhard in later years was die author of a work, 1'itt Human Phenomenon* of die hind seventeen th-ccSfflry scientists won id have dismissed contemptuously as a ‘'philosophic romance." Unless a confession by the real culprit comes to light, the [me answer is not likely ever to be known, All Lite same, the term ‘‘hoax," widely used to describe the episode, is uEitinly cuphemisric: this was a carefully executed crime carried out with the intention ol‘ deceiv¬ ing.

PINEAL BODY A dorsal outgrowth of the ditncephalvtt, which lies between the end brain and the thalamus, the pineal organ had an eyelike character in lower vertebrates, or was in any event light sensitive. In present-day mammals it is I bought to Lx; an endocrine gland affecting pigmentalion. The pineal body is more evident in mail than in lower animals, and its prominence lit embryonic development is something that could hot have been known to Descartcsij Perhaps 1 ids is why he pmjioscd the pineal body as the scat of the soul (he may have been influenced by the fact that he did not believe animals had souls). Descartes’s “soui" was not anything that could be con¬ tained in a material body, as the gallbladder contains bile; rather it was an animating principle- “a wind, a flame, or an ether’’ in which resided the power of t bon gin, especially of imagination.

—

—

FOIESIS

derives from the Greek A suffix familiar in biology, standing pttieshi for making or creating (it is the root also of root the English words "poesy" and “ poetry"). Tile activities referred to as erylliropoiesis, lymphopoiesis, and tin: like refer to tin: gen¬ eration of red blood corpuscles, lymphocytes, and so on. As lo the poetry, it is clear dial when Percy Bysshe Shelley in his Defence of Poetry said i hat “poetry comprehends all science," he was mi plv215

POPl-I.ATION

GK&WTH ANI1 CONTROL

ing that the act of creation involved in the composition oTpnctry was in its essence akin to tint imaginative exploit that is the origin

orall scientific ideas.

POPULATION GROWTH AND CONTROL The growth in numbers of biological populations illustrates an important anti perhaps a defining characteristic of biological growth: that which i.sfarmed bygrowth J.r itself capable offurther growing This is the distinguishing mark of growth by continuous com¬ pound interest, for if the starting number is regarded as capital and the additional members of the population formed by growth as interest, then clearly the Interest is added to caput til arid begins to earn interest on its own India If. Growth of tins hind is often re¬ ferred to as exponential nr logarithmic. The sense of this nomenclature is immediately obvious if we consider the simple case of a population of organisms, each membet of which divides into two in each LLIIIL of time; the size of the population at each unit of lime will hr as shown in (he accom¬ panying i able. Tile logarithms in the last line are necessarily the same as the exponents in the second last line, for these logarithms are taken to the base 2, the logarithm being the power to which 2 must be raised in order to give the Number of organisms in the population. Time units Number in population

Exponential form ulatiun I /iga rit hrn to base 2 It (he

0 I

,y> 0

12 2 4

21

2*

12

3

4

3

10

B

U>

32

1,024

2:I

24

}"

3

4

5

n IN

10

be seen by inspection that if one draws a graph relating logarithm of population size to elapsed time, the jxiims will Can

fall along a straight line, whereas if we had Instead plotted the arithmetic number against lime, the points would form curves sweeping rapidly upward as exponential curves do No real population could grow in exponential style for long: in real life the growth of populations is always restricted by the ac¬ tion of one or more density-dependent factors, usually having LO do 2 US

POPULATION GROWTH ANO CONTROL

with living space, inadequacy i>T nutrition, accumulation of toxic waste products, stress associated with overcrowding, and so on, ft is thus a mere figure of speech to say that human populations can ever become so numerous that they will occupy the entire land surface of the globe shoulder to shoulder,, perhaps even two deep; it is no ligurc of speech, though, to say that the density-dependent factors most likely to act upon human populations will lie famine and pestilence ol ujp imaginable severity. The past hundred years have been marked by the partial an¬ nulment df some of the most important density -dependent factors that act on human populations Thanks lo the exertions of medi¬ cal men and sanitary engineers, we have achieved a measure of death control that has not l>een counterbalanced, tin luckily, fey the degree of birth zrwirol necessary to keep the human population within reasonable bounds. The population explosion is the wellknown and frightening outcome, and a striking example of the unpredictability of many ol the malefactions consequent upon the growth of science. The exigence of the population problem prompted many poli¬

ticians and prominent personages to call for the stabilization of human populations. This is a feasible-sounding enterprise, and we should all be very fortunate if it were as easy ns going to tile moon, A population can become stable in numbers only when

appropriately matched regimens of fertility and mortality have been at work long enough for the population to achieve it stable age distribution, whereupon it will reproduce itself faithfully to that pattern. No human, population lias ever achieved this stable slate, and i ti our opinion there is never likciy to be a time in which wc are rtot worried alternatively by fears of a precipitous decline in the human population and fean that the population will grow to a politically and economically unmanageable size, At one tune the idea gained ground, specially in the Uni ret! Staitts, that if all couples would restrict ilicniselvcs to having two children, stability of numbers would be achieved. "This pro¬ posal ft has been rauarked, “has about it that air of commonsen steal rightness which is almost invariably a symptom of some aberration of reasoning," The aberration is that no weight is given lo mortality or infertility, important though they both are. An average completed family size of two would be a sure recipe 217

PRIMATES

for the catastrophic decline in human numbers which demogra¬

phers feared in the L930s, Consider the difficulties that would be faced by a hypothetical Minister for the Control of Population; in the first place, he would have to provide for the discovery of better methods of birth con¬ trol in the face of the natural conspiracy in favor of fccundiiy (to which we owe Our own presence here on earth), and these methods would have to be made available to populations who do not know how and may not want to learn how to use them: that 33 one is a formidable political, religions, and educational enter¬ prise. In a free society, one in which the members cannot be re¬ quired either to reproduce themselves ur to abstain front doing so, the Minister of Population would have to work as best he could through fiscal and educational means by bribing, coaxing, cajoling, or pleading whh people to have a greater or lesser rut tuber of children as the prevailing situation required.

PRIMATES This is a term introduced bv Linnaeus to signify monkeys. apes, and human beings. Professional zoologists often pronounce the word in three syllables, Latin style, though there is no serious like¬ lihood of confusing the connotation of Linnaeus? term with that which describes a synod of the principal of E iters of Anglican and Episcopalian churches. Linnaeus allotted primates the first rank among animals: in second place lie put mammals other than pri¬

and these, appropriately enough, he designated .acundaies. Ail other animals were of the third rank, iertiatfa (We learned of Linnaeus' distinction between primates, sccmidaies. and temaLcs from J. /.. Young's Life of Vertebrates, 2nd ed. [Oxford, 1962J.) Primates are an order of the class Mammalia: thev arc typically tong-limbed arboreal animals with many adaptations associated with the arhorea! habit and movement by brachiation, Among these are ap posable hig toes with ihumblikc fti net ions, dominance of the visual faculty, and binocular vision with forward-facing eyes a characteristic that endows animals for the first time with something that is recognizably a face. 'The primates descended from an insect ivoran slock, probably from animals much like the tree shrews. Curiously, though, the mates

—

218

PKOtfeLNS fact's of pri mates arc the basis of a taxonomic distinction: pri¬ mates with a narrow nasal septum art1: Cat ar bines and mm prise

the Old World monkeys, atuJimpnid apes, and man, Those with a broad nasal septum and a fiattish face ate the \ew World mon¬ keys, Platyrhines, It was surely Lheir similarity to man and to the animals closest to nmn (the Anlliropomotphil) (Inti induced Linnaeus to desig¬ nate primates as the first among animals. This must in turn lead ns to designate human beings as the hrsi among primates, a rank of Which only bad judgment or an adolescent style of cynicism could deprive them. Among the most manlike

characteristics of the great apes (especially chimpanzees) are, as Jane Goodall has observed, the beginnings of exogeneiic heredity: the transfer of information from generation to generation through nongenet ic channels. This is the very characteristic to which human beings owe their posi¬ tion as first among primates,

PROTEINS

1M the entry dealing specifically with them, we said of iviiCLRlo ACIDS that their essential function was to act as vectors of genetic information in communication between generation and genera¬ tion and between nucleus and cytoplasm. The baroque profusion bf different kinds of proteins and ihc multiplicity of their functions areis$j£h that no such tidy story can be told: the contract tie element of muscle fiber proteins is respon¬ sible for all muscular movement, whether m locomotion or ttt the working of heart and guts: as enzymes, proteins are involved in almost every metabolic transaction nf the body. They are the principal structural const iiuent of cells; they are responsible for the clotting of blood and lymph: and as cottnective-t issue libers (collagen, el as tin), they prevent the Organism-as-a- Whole from

falling apart. Proteins arc huge polymeric molecules, ‘'polymeric" because they arc built upon (he repetition of unit building blocks, “mono¬ mers. These are the amino acids, of which there arc some twenty different kinds, each one coded for by a triple! of nuclfotidts, in the nucleic acid molecule that specifies (Jfcir assembly in a >f

219

PROTOPLASM

particular order. The primary structure, of protein s is. given by the linear order of the amino acids along the carbon chain into which a protein molecule might in theory be unraveled. A proleirTs seeon d ary structure specifies the pattern of branching, and the ter¬ nary structure the paLlern ol its folding into a three-dimensional .structure, The complete three-dimensional strut:lure of myoglo¬ bin and oT the protein capsule of adcnovifUS- 12 arc now known both splendid feats of analysis. Proteins dlifer sctlTicietit ty in size to make centrifugation of their solutions an cHcctive method of separating them. Bearing as iliey do a net positive or negative charge, liiey migrate slowly in electric fields Willi the effect that electrophoresis may also be used for separat ion.

—

Proteins, typically, arc soluble in Water but ihc protein keratin that is the principal ingredient of hair, nail, and daw and the out¬ ermost layer of the skin is not. Water-soluble proteins cease to be so when denatured by heat or by tile action upon them of the salts of heavy metals, familiar examples ol denatured proteins are the

white of

a hard-boiled egg and the skin that forms on hot milk lefi standing. A process akin to dr n a (oration occurs when

when the water-soluble protein pbrimgtn is converted by enzymes into the insoluble fiberform, which is the structural basis of a blood or lymph clot. Proteins, moreover, are Characteristically antigens. Their im¬ munologic: properties may be used to distinguish them in a much more sensitive arid discriminating way than is possible by any merely physicochemical procedure. Proteins are nut.ntt.pus and as skeletal muscle- the form most highly prized as a food they arc normally associated with a quantity of" Ini that quickly dispels the illusion dial “Imichcrts meat,” far Front being fattening, is positively thinning in elm me¬ ter.

PROTO PI iASM Mure than fifty years ago (be biologist and mathema tical logi¬ cian Joseph Woodger wrote: “Biologists certainly speak as if there were in mil u re a stuff to which the term 'protoplasm’ is given.

ZtG

PROTOPLASM

V'\rlicn wc-flojiic LO look into the question tliei'e does nut seem w be any justification for this belief” (Biological Frinttfiiejfi | London, 1929], p. 293), Unexpectedly, HiriS Driesch, the vitulist, had anficipatcd duL modem practical usage: “Protoplasm is a mere name for what is not the nucleus.” Wo have pointed cun elsewhere that in real life the word is now only used as a general term for the ceil sap, bin in the old days when it was belie ved there was a substance to which the term “protoplasm” might property be applied, there was a good deal of discussion about its fine struct me. There was a granular theory, a ttticular: theoryÿ and indeed as many theories as there were fixalives for hardening tissues in order to make microscopic prepara¬ tions of them. For such fixatives almost invariably contain coagu¬ lants of protein, and it was the different protein precipitation patterns that gave rise to the different theories of pnot o plasm ie structure. Thomas Henry Huxley had no doubt about ihc physi¬ cal reality of protoplasm; “1 have translated the term protoplasm which is the scientific name of the substance ... for the words Review, I Feb, 1 869}. Proto¬ 'physical basis of life’ ” plasm was a kind of nature-philosophical ether; just as the ether was thought to permeate all material structures in the world and act as the medium propagation of electromagnetic waves, so the living substance protoplasm was thought to per men i e other¬ wise inanimate structures and endow- them with vivacity. The influence upon Ernst Haeckel’s mind of the idea of protoplasm, abetted by that of a great chain of being, led I tint to sus¬ pect the ex isle nee of very lowly organisms consisting of “naked protoplasm” -of UTichfeim, the primitive slime only, finch orga¬ nisms he professed to have discovered, and he cal led them Mwwa. Not to be HIU tdone by wlnit was EIL that time a rather competitive science, Huxley in the Quarterly journal of Micmcof/ical Sdeftce tiescribed a specimen of m onera from a deep North Atlantic dredg¬ ing, and out of respect for the learned zoologist of Jena he named it Bul/tfbiui ftaeckeli. Today the Word "protoplasm” is falling into disuse, a fate that would certainly not have overtaken it il it had served any useful purpose, even as a hrsi approximation to reality. The demise of the protoplasm concept resulted from the slow realization that life processes have a structural rather than a colloi¬ dal basis; even Frederick Gowland Hopkins5 famous pronounce-

{FoAhtfy

—

221

PROTOZOA

menl that life is a manifestation of a. complex dynamic equilib¬ rium in a polyp h as jg system no longer carries much weight. The earliest attempts at X-ray crystallography of bodily constituents combined with electron microscopy soon made it clear that the

Orderliness of living cells and their products is essentially a solid or crystalline orderliness, and that the hit It: organelles in the cell arc minute ‘‘solid” bodies Looking as if it was only their size that pre¬ vented our picking them up and handling them. Thus the speci¬ ficities of metabolism in time and space of why metabolic events happen here and not there, now anti not then has a structural basis, jRjmetbing. very far removed from primordial shine.

—

PROTOZOA Thai rnoieiv of the lay public Which knows that the formula iLO designates n molecule of witter knows also lhat ‘'the amoeba" is an elementary and rather lowly living organism "a mere spetk of protoplasm” is the popular cliche. Amoeba is in¬ deed a protocol in. and it is very small indeed. Schoolchildren anxious in make a good impression on rhrlr teachers or examiners should guard against making remarks such as “If one pricks the amoeba with a pin , , This is a form of words which instantly reveals a total lack of com prehension ol how small amoebas arc

—

and how large, relatively speaking, pins are. Co iw I tiered collectively, protozoa are adjudged to constitute a phylum, and although they do not lend themselves to the fullas it applies to many-celled ani¬ dress hierarchy mals, they may be usefully and naturally subdivided into a n um¬ ber of classes that are distinguished mainly by the ways in which they move, Reference has been made elsewhere to the quasi -philosophical non problem of whether individual protozoa are to be described as nonce! Eular or as single cells, Nothing turns on the decision, which embodies not much more than a nuance of meaning: those who think of cells as mechanical or administrative subdivisions ol an organism tend to refer to protozoa as noneellniar because they arc not so subdivided; (in the Other hand, those who think of the cell as the tectonic unit, and of a many-ccllcd animal as a colony

222

PKOTU/OA

of col Is enjoying £ji high degree of intcÿrÿljon and division of labor, lend to refer to protozoa as single celled. Upon one subject, how¬ ever. all zoologists agree: protozoa with all that dial implies of wholeness and degree of integration of parts -and also of self- reproduce ion. One of the classes into which the protozoa are convent ion ally subdivided, the Spoiozoaj is something of a ragbag of mainly par¬ asitic forms which ait not easy to enter under the names of other

—

classes,

Many protozoa arc parasites, and u is mainly as cl iscase-ca us¬ ing agents that they obtrude themselves upon the attention of human beings. The trypanosomes that in feel cattle, Trypanosoma bmai and T. congÿenst, arc not wholly maleficent; in a sense they tend to protect the resident immune ('attic [>opn!ation against competition fmni immigrants or Imports from elsewhere. Trypanfisomts arc responsible for two very serious human ill¬ nesses; the better known is sleeping sickness, the work of T, gambifriie or t. ThodesitHif. Tsetse flies are notoriously t he vectors of trypanosomes, which may invade brain anti central nervous sys¬ tem to cause extreme lethargy and sleepiness (hence mcephatilis Uthargicafi In -South America 71 ftltti causes a disease of protean manifestations, Chagas’ disease, whtcEi invades heart muscles and visceral gaff<a. Charles Darwin was alniosi certainly a victini of Chagas' disease, a Jjyptj&hcsis indignantly repudiated by a num¬ ber of physicians for a variety of ostensible reasons that conceal what we believe to be the principal motive: strong resentment (hat medically urujualihed scientists have so far forgotten them¬ selves as to have attempted a medical diagnosis, Tilts may be combined with the uneasy and well-founded feeling that Dar win's treatment at the hands ofh is own physicians (embodying as it did the theoretically unfounded use of arscnicals and mercurous compounds, not to mention trem merits such as “Dr. Gully’s water cure1') shows the medical profession in a rather un favorable light. We are amused to notice that Brazilian medical opinion has ea¬ gerly accepted the hypothesis of Darwin’s having been a victim of South American trypanosomiasis as if his having suffered a dis¬ ease so closely associated with the names, of iwn famous Brazilian medical scientists (Carlos Chagas and Osvaldo Cruz) were a source of some national pride.

—

32,1

PTERODACTYLS

Trypanosoma] in feelions sometimes respond to 'treatment by organic arsen Seals, though these may have grievous side effects. Protÿcoan parables are responsible also for malaria* but not for syphilis, since spirochetes have for some lime been regarded as bacteria.

PTERODACTYLS

—

Reptiles twice look to flight. Quo line of descent that which leads to birds is represented by an intermediate form such as archcupleryx; the other line of descent is that represented by pterodactyls. Although fferanodon had a wing span of more than twenty feet, pterodactyls giro era!ly are quite small. Their muscu¬ lature, the essentials of which can he inferred from the structure of the skeleton, is such as to make il certain that they could not fly by flapping wings. fhe likelihood is that pterodactyls were glid¬ ers, equipped with a llight membrane supported in fro pi by an extremely elongated fourih High of the hand. The aerodynamics of (heir flight as it relates to takeoff and landing has not yet been

—

fully worked out.

‘224

R

ECAPITULATION

Ernst Haeckel's Law oJ Recapitulation declarer that in the bourse of its develop mem an animal passes through develop¬ mental stages tui mist aka bly comparable to the forms of its pre¬ sumed evolutionary ancestors, His own accouni of the matter was fully expounded in ihe fiftli edition of ti is liiolution of Man (trails,

Joseph McCabe; London, 1906). As we have said elsewhere, the sense of the law is sometimes given by ‘'ontogeny recapitulates phylogcuy," or by the Schoolboy variant lhul jn development "an animal climbs its own family' tjfijee.'” A mammal begins life as a single cell, the ovnhrij ostensibly a structureless blob ol "protoplasm" liiaL might be Compared to a single protozoon. In the course of development all vertebrates pass through a metamorphosis which in effect converts a hollowball of Cells Lrilo a double- layered structure such as Ought be created by pushing in the ball at fine pole. This forms a so-called gas mil a and thereby establishes a firm kinship to essentially twolayered animals such as many polyps and hy droids. EvcuuiaLEy the embryonic axis is fait! down. The embryo ai this stage is a bi¬ laterally symmetrical structure with a well-defined head bearing paired sense organs, a dorsal central nervous system, and a me¬ dian dorsal backbone. This, Haeckel pointed out, was essentially ihe condition of ihe iaticclei (amphioxus), universally agreed to represent an ancestral chord ate form. In subsequent development vertebrates go through a (ishlikc stage, the expanded anterior end of the gut tube being perforated by structures looking like gill slits.

Haeckel believed that not only the soma but also the psyche obeyed the principle! of recapitulation; again in The Evolution uf Afan he wrote: “The wonderful spiritual life of a human race through many thousands of years has been evolved step by step from the lowly psychic life of the lower vertebrates, and the devel22JS

RECAPITUL/VTEON

opmertt of every chi Id -sou I is only a brief rcpct'iiion of that lorig and complex phylogenetic process,” One of the most important critical lexts on recapitulation is Gavin de Beer's EmbryoJT and Ancestors fird cd.; Oxford, 1958). Sigmund Freud accepted the idea uncritically: in Civilizejf* lion nod its Discontents (ed. James birachey; London, 1965), at¬ tempting to justify Ins belief that modern civilization is the victim of neurosis, he argued as follows: “II the development of civiliza(ion has such a Tar reaching similarity wii h the devwipmertt of an individual should wc noi be justified in coming to the conclusion that in some civilizations or epochs of civilization possibly even the whole of mankind has become neurotic?” Haeckel's La.w ol Recapitulation is not satisfactory, but as, wc point out in the entry nvptn tiFM.s ANDTHEORY, it cannot be pro¬ nounced blunily to be “wrong,” for it embodies an element of truth significant enough that we can readily understand why it

should have been propounded. The element of truth is the same as thai which is embodied in vf the devclopmcijj of a pecto¬ ral (in, cognate reasoning applying in the development of ihe human arm; The various phenomena grouped together as "recapiiulatory” in character and point i tig to an affinity between mamnuilian development anti the development trf lower verte¬ brates (for example, the appearance of visceral clefts in the devel¬ opment of higher vertebrates) seemed to Thomas limit Morgan the most convincing single piece of evidence in favor of the idea of evolution. T. H. Huxley also thought so, In spite of its substantial measure of truth, therefore, the Law of Recapitulation has faded away, or rat Iter has been ass i ltd la ted into a law of greater generality that which we associate with the name of von Baer. Jusi in time, loo, for as Stephen Jay Gould has pointed out in his authoritative text Qritogefy' and Phylogfny (Cam¬ bridge, Massachusetts, 1 languish in a familiar and noil LII real etiing septa I or of in com prehension. Their travesty is embodied in the declaration that reductionists, mechanists, and other philo¬ sophic evildoers represent the whole as "a mtn: sum of its constitu¬ ent parts." Summation is of course a perfectly respectable ftme227

KEBugrnoNisrtt

(tonal iclai.it>!] all i p

which might well obtain between parts: and might furnish a complete description: tile mass of a whole, for example, is the sum of the masses of iu const itwent parts, and the osmotic pressure of a solute is a function of the number of ions and molecules in the solution. Not even a hoiisr would maintain that a composite body bad a "true11 mass as op¬ posed to a “mere mass, with the true mass being something more than the sum of the masses of I he parts, Yel something close to this absurdity was at one time thought to account for the empiri¬ cal fact that i he combustion of a metal, such as magnesium, leads to an increase of weight. This phenomenon was diflicult to ac¬ count for in terms of the phlogiston theory, according i which phlogiston should have been given off (phlogiston, the essential principle of fire, being for inorganic chemistry roughly what Hans Driqsch’s en telrchy was for biology), Iddogiston. it jfras proposed, weighed less than nothing: small wonder, then, that tile loss of phlogiston on the combustion of a metal led to an increase of which in

sonic tastrs

weight.

ILL biology very few properties of composite systems can bo represented as merely additive functions of the properties of constitu¬ ent parts and those i haf can be so represented are of no very great interest. The functional relationships which obtain be L ween parts and which must be ascertained ifa description is to be com¬ plete are extraordinarily complex, and their clueidafi on is propor¬ tionately laborious. Indeed, the whole enterprise is so difficult and tedious that it may sometimes embody too extreme an ambition, In the tenth edition of his fystm of Logic (London, 18415) John Stuart Mill wrote as follows oT sociology: “The laws of the phe¬ nomena of society are and can be nothing but the Laws of the ac¬ tions and passions (jif human beings gathered together in the social state , . . Human beings m society have no properties but (hose which are derived from, and may be resolved into, the laws of the nature of individual men,1' A simple paraphrase converts this declaration into the form that used to cause needless dismay and resent merit among "or¬ gan ism ic" biologists: “The laws of the properties and perfor¬ mances of living organisms are and tan be nothing hut the laws of per lb nuances of living cells gathered together inio the slate characteristic of living organisms. Living organisms have no prop-

—

22K

Hl.lllJC I KJ.NISM

ertics but those which are derived from and may be resolved into the properties of individual cells,'1 I'he principle of redueibllity Obviously could be taken one or two steps lower In the hierarchy- -for cells can be resolved into molecules a nth mutaiis mutandisÿ much the same could be said about cells as was said about Organisms in relation to cells; then again, molecules might be resolved into their constituent atoms, and they in turn no doubt into element ary par titles It should be ten leu) be red, moreover, that the relationship "re¬ ducible to" is of the kind described by Ibgiciansas transitive: thus if A can be analytically reduced to B and B to C, then A can lie reduced to C. This being so, it follows that a concept belonging to the social, political, or ecological domain of discourse can be in¬ terpreted in terms of the atoms and molecules of which the mate¬ rial world is composed; to pul it concretely, such an upper-level concept as the foreign-exchange delicti should be mlerpretablc in terms of the properties and interactions of atoms and molecules, and so should the Idea of proportional representation— yet, oddly. there is no mention of these matters in any textbook of economies or physics or political science. It is evident that reducibihty has EIS limits. The success of re¬ ductive analysis in biology is due mainly to the fuel that the prop¬ erties of organisms that interest us most are exactly those that do respond to reductive treatment; the system of signaling in the transfer of gentuic information, or the physical dispositions that make possible the nervous coordination of the parts of the body. By representing a composite whole as a fu net ion of its constitu¬ ent parts; we are almost automatically empowered to envisage a domain of possible wholes other than that which formed the origi¬ nal subject of the analysis. Indeed, perhaps the simplest way to epitomize reduction ism is to envisage any particular frog as one realization in a universe bf Possible Frogs, any one of which might have become real, though In fact only one did; likewise the whole world is seen reduetively as one only of a whole domain of possi¬ ble worlds not necessarily the best.1 his way of looking at reduc¬ tive analysts makes it clear that among all conceivable ways of understanding the world, reductive analysis is the one dial makes it easiest to see how, if need be, the world flight be changed, 11 is of course the character of the interaction among l hr- eom-

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229

RR1WCTIOMSM

ponents that fixes the character of the structure, phenomenon, or performance under consideration: thus only a very limited sub¬ class of the possible interactions among cells permits their inte¬ gration into a living organism and likewise only a minority oT the possible interactions among persons i.s such that an organized society or ecological community will emerge. Before discussing emergent properties, we must make an impor¬ tant point about the empirical content of the various levels of the hierarchy into which the system of animate nature may be said to rail. In increasing order of particularity wc may tabulate the hier¬ archy thus;

—

Sociel y / comm u n i ty

Organisms Organs Cells Cellular organelles Macromolecules Molecules Atoms

Subatomic particles A significant property of this arrangement is that the higher levels include the lower levels; societies are composed of organisms, or¬ ganisms of organs?, organs? of cells, and so on. The sciences that

deal spccilically with each level, starting at the bottom with par¬ ticle physics and ending with sociology or ecology, increase in empirical richness as wc ascend the rungs of the hierarchy. Each may he said to comprehend the concepts and factual matter of its own subject plus the concepts and factual matter ofall lower-level disciplines, with sociology/ccology necessarily being the richest of all, for everything that is true of organismic biology is true also of sociology. It is a sociological not merely a physiological—truth that living organisms that inquire food exert themselves to pro¬ cure it, and k is also a truth of sociology' that the liver is rapidly damaged by ethyl alcohol and a whole variety of other organic solvents. It is a truth of organismic biology, no less than of chemis¬ try, that the interaction of an acid with an alkali produces salt and water:

—

A£[>UCT10N1SM

NaOH + HCI = NaCl +

H:0.

This is also a truth of politics, though not one that is likely lo sway the electorate. As the empirical content (the repertoire of actual or possible objects of observation) increases, so also does the conceptual conlent -not necessarily in predictable ways. Indeed, each level of the hierarchy has concepts peculiar to itself and not interprctablc in terms of the lower levels; foreign-exchange deftot has already been mentioned (it belongs to the political level, and propositions retaring to it make no sense at any lower level). Again, at the level of atomic physics and chemistry it is possible to understand how one atom of carbon may unite with two atoms of sulfur to form car¬ has a notoriously bad odor not interbon bisulfide, CSÿ but level, to which even the concept physicochemical any prctable at oT smell does not belong; for smell, along with sexuality, memory, and fear, is contextually peculiar to the level of organism ic bioTogv. Properties or phenomena that appear at higher levels of inte¬ gration and are not predictable or interpretable in the lower ranks may be described as emergent. C, Lloyd Morgan, a champion of the notion, drew a useful distinction between resultant and emergent properties, the former being understandable and indeed predict¬ able in terms of lower analytic levels (properties such as mass, os¬ motic pressure, and combustibility), whereas emergent properties cannot be predicted or interpreted by reductive analyshThe concept of emergence is not offensive. It is unpopular only because those who have successfully employed the stratagem of reductive analysis tend to feel that the designation “emergent1' implies a loss of face (a feeling quite uncalled for). The real objec¬ tion to the notion of emergence is that it has no explanatory' value: it marks the end of one train oT thought, not the inception of a new one. We arc not more deeply understanding or wiser people Jbr resolving that the possession of mind is an emergent property, for so it clearly is: there is no psyche or rudiment of psy¬ che in a crystal or in a molecule. Nor is there any rudiment of love, though Pierre Teilhard do Chardin maintained that if love were not present in some primordial Form in atoms and mole¬ cules, it could not have made its appearance ai the level of evolu¬ tion represented by mankind. Thus the union of a sodium ion

—

231

ftLKLEX

with a chloride ion Would he const rued ns a premonition of that union between higher organisms jfthith was the outcome of defended by an English admirer of Teilhard love an by pointing out (and we do not deny it) that if sodium and chlo¬ ride ions had not possessed a propensity to unite, love could hard I s' have appealed Ut a later Stage in evolution. This defense unhappily em bodies a Serious confusion dS ihought: failure in dis¬ tinguish between necessary preconditions and sufficient precondi¬ tions for a phenomenon, event, or slate -til afiairs is an egregious logical error, The idea of emergence plays a useful [tart in die biological sci¬ ences if Only bv giving a name to that which does not respond to reductive analysis, though it must be added that biological re¬ search of all kinds prospers proportionately as more and more of its subject matter docs respond.

— argument

REFLEX The definition of a reflets proposed by B. I'. Skinner may be put as follows: in anv episode of behavior where S represents a stimu¬ lus and R a response, we can speak of a reflex action when R = f(S), that is, the response is a specific fi met ion of the stimulus. The r ell ex concept is of much wider application than in neuro¬ physiology: thus immunologists have sometimes spoken of an “immunologic reMex”' when relerring to the specific relationship between llic antigenic stimulus and the immunologic response it gives rise to, It has been helpful tn immunologists to distinguish an afferent from ail efferent arm of the immune response: the for¬ mer relates to events having to do with the presentation of ant igeii a i the response center, and die latter to events having to do with the way in which the immune response is put into effect. A number of subordinate notions have grown up around the reflex concept; the term "reflex arc," Tor instance, lias been used in describe the supposedly one-track pathway by which a stimu¬ lus excites in turn a sense organ , an afferent nerve, and, after making synapse in the central nervous system, an efferent nerve and a motor end organ of some kind. Holism and nature- philosophy sharply repudiate an opinion

232

RHtSUfi FACTOR

attributed to, but not ht-Jtl by, Charles Sheri ngton of any memfeer of lib school (nor indeed by anyone excepL nature-philosophers inventing imaginary opponents on whom to launch attacks). This is t tic: opinion that ail relief behavior can be rCsoJyed into [ho M:m nf individual tt$kx arcs, someth Ihg which is of course very fa i from being i he: ease. Indeed, the reason the "reties arc" term iiiblogy went out of use was precisely because Sheri ngt on himself and his school showed very dearly how interactions in the central nervous system and tilt con verge ncc ol afferent pathways upon a singlet efferent pathway made the reflex arc a hopelessly unrealistic concept. The term "conditioned reflex” refers to a state of affairs in which a reflex response is excited not merely b\ the si i ton lus that originally gave rise to it IJLII by a conditioning stimulus that had repeatedly been caused to precede tint original siinmiiis. Gondilion!tig gives rise to the neurological equivalent of an expectation and provides also for a rudimentary form of afferent learning, that is, [earning to increase the repertoire ul stimuli to which a

certain

moior

response may be given,

RHESUS FACTOR When blood of rhesus monkeys is injected into rabbits, an anti¬ body is formed that reacts upon the red blood corpuscles of ap¬ proximately flu percent of human beings, These are rhesus posi¬ tive, the remaining 5 fi percent being described as rhesus n'egattVC-

ln keeping with the nomenclature of other blood antigens; several I actors ihat make up the rhesus antigen are usually referred to as C7 D, and E of which the mosL important clinically is D, Whereas antibodies to blood antigens A and B occur naturally in some human beings, ami rhesus Antibodies are formed only by ;tt> five immunization (for example, by transfusion into rhesusnegative individuals of blood which, though compatible for other important antigens, contains the rhesus uuLigcn), Or rhesus antibodies may be formed when a rhesus- negative mother bears a number of children who inherit (he rhesus amigen from their father, I minimization of the mothei may occur during parturition by leakage of fetal blood cells into the maternal circu233

RMtMJS FACTOR

lation. When this unhappy state of affairs occurs, maternal anti¬ bodies entering the rhesus-positive fetus may cause extensive de¬ struction of red blood corpuscles, which accordingly brings about a burst of proliferative activity among blood- forming cells

{erythroblastosis fetalis), Sensitization is much less frequent when mother and infant arc incompatible with respect to red-cell antigens of the R, O sys¬ tem the reason being that if Total red cells are of group A and the mother is of group R or group O, she has ready-made ami-A antibodies that will destroy fatal red ceils in her circulation before they can arouse antirhesus immunity. This protective effect, it has been thought, can provide the selection pressure that keeps A, II, O polymorphism in being. The selective advantage that main¬ tains rhesus polymorphism itself is not known unless perhaps it is a transient polymorphism that will eventually die Out,

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234

SENSE

ORGANS

An instrument of the kind described by engineers as a trans¬ ducer, a sensor translates one energy form or waveform imo an* oilier. Sortie examples are the p heliograph pickup and jhe micro¬ phone, which translate mechanical and atmospheric pressure vibrations respectively into voltage pulses. This is analogous to the action of biological sense organs, with the dill'erence that the latter translate environmental changes of state into nerve im¬ pulses. A sense organ is specially adapted to respond to one kind of environmental change of state rather than another to tem¬ perature. for example, or to light, pain, sound, posture (as dis¬ closed by muscle and joint .sensors), to orientation in space and angular acceleration (both the work of the car, an equilibratory as well as an acoustic organ). Furthermore, a sense organ lowers the threshold ol strength til stimulation needed to initiate a nerve im¬ pulse: sensory adaptation (a process in which a sense organ ceases to respond io a stimulus of uniform intensity) is described in (he entry on ADAPTATION. It is a phenomenon that reminds us that sense organs can respond only to a change of state. One of the most important generalisations that can be made about (he physiology oT sense organs is that embodied in Johannes Muller's Law of Specific Irritability, or Law of Spe¬ cific Nervous Energy, In effect, this law states that, the modal¬ ity of sensation w lift her of light, sound, pain, or posture is determined no| by the sense organs, vrhich after alt can only generate nerve impulses, but by the nerve itself, or rather by its central connections. Stimulation of the auditory nerve pro¬ duces sensations of sound, and of the optic nerve sensations ol light, by whatever means the nerves are stimulated. Much else in sensation is centrally governed: thus different eortieal reccplors provide for (he perception of a line that is vertical and one that is tilted.

—

—

SENSE ORGANS

in all these respects ii can be seen ihat sensation follows a Kant¬ ian pattern. Immanuel Kant's contention in The Critique of Pure Reason was thai that which we perceive or become empirically aware of is determined by the character of our faculty of intuition or perception- Kant wrsuld have been delighted to know to what a degree modern sensory physiology has confirmed his insight. He went on to say, as we need not, that some knowledge can be a priori, that is, independent of all experience. Lancelot Hogben argued that this position is undermined by the existence of a sense that Kant was unaware of, namely proprioception, the joint and muscle sense upon which postural self-awareness is based; but tve dn not find this argument convincing. The central tradition of British (as opposed to Continental) philosophy, especially as associated with the name of John Locke (UJ!32 1 70 V) , is the empiricism embodied in the line Nihil in uitellectu quod non pritts in xensu There ES nothing in the mind but what entered it by way of the senses. Biology cannot sustain this belief. While wc do not agree with Kant that there can be knowledge in¬ dependent of all experience, the empiricist axiom fails by disre¬ garding the existence of behavioral programs that constitute a kind of “inherited knowledge.” Such is the case with a mouse’s knowledge of nest building, or a bird’s of its particular song, Whatever part upbringing and sensory experience play, a large part of their specificity the property of being this song and not thnl —resides in the chromosomal recording (one might almost say tape recording) that is part of an organism’s inheritance Equally, there is nothing in biology to give scientific authority to Cartesian rationalism, which accepted as true that which rested upon an in¬ tense inner conviction of the self-evident truth of certain proposi¬ tions, combined with an inability even to imagine any skeptical argument that could shake them. It is well known that one such proposition, avowedly the first principle of Descartes's philoso¬ phy. was Cogi to ergo sum I think, therefore I am. Because all that wc know of the working of the senses is based on sensory evidence, it is of no use to appeal to physiology to res¬ cue us from the Berkeleyan idealism according to which the ex¬ terna! world exists only by virtue of the ideas of it we form in our minds, Wc cannot better Samuel Johnson: "I refute it lhus\” said Johnson, kicking a large stone so violently that he rebounded

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—

—

236

sExt'Ai. CYCLES

from it

—

‘'iKiis,”

‘i

has been remarked, simultaneously befitting

George Berkeley and cor mbo rating bir Isaac Neiÿdh’s Third Law of Motion ("Every action gas an equal and opposite reaction1"),

SESSILE ANIMALS One docs not have to be a professional zoologist to call to mind without difficulty a variety of animats (hat arc sedentary because they are permanently attached to the substratum on which they five; among them arc sea anemones, hydro ids and polyps gen¬ erally, barnacles, sea squirts, sett lilies (crinoids), and limpets Ses¬ sile animals share a number of structural and physiological adap¬ tations: they show a tendency to radial symmetry and develop cither tough external skeletons or thick, resistant, and virtually in¬ edible sheaths or tunics. The power of regeneration, and the asex¬ ual reproduction that so often goes with it, is highly developed, Hermaphroditism tends to be the rule, accompanied by various devices LO prevent self-fertilization: the fertilized eggs usually de¬ velop into mobile larvae, which undergo a radical metamorphosis before fixation to die substratum.

SEXUAL CYCLES

Whether CStrous or menstrua!, sexual cycles may be thought to have evolved in response to the selection pressures arising out of the necessity to conserve and to facilitate fertilization of the lim¬ ited number of oocytes with which the female is endowed, be¬ cause mate mammals manufacture sperm throughout life, there is no imperative reason to conserve it. It is not therefore surprising that males arc not cyclic in their capacity or apparent inclination to mount females; female mammals, On the other hand, arc re¬ ceptive only at intervals that recur cyclically during the period known as estrus from the Greek uistm, the gadfly that bites cat¬ tle and maddens them in a way believed Sit classical times to sim¬ ulate the exigence of sexual desire. Ovulation, the shedding of an oocyte, occurs just .before the onset of heat. Although in New World monkeys vestiges of this

237

SKXLAUTV

receptivity Linger, human beings, apes, and Old World monkeys arc characterized by a menstrual cycle of a somewhat different kind. The word "menstruation11 itself refers to the peri¬ odic shedding of the kndometrmm, LIIC highly vascular internal lin¬ ing of l he uterus into which the fertilised egg is implanted. A number of vascular adaptations reduce to a rmmimim the loss of blood. Ovulation occurs halfway through the menstrual cycle, in art episode sometimes accompanied by vniuclschmer?,, or m idpa m. The occurrence ol'some vaginal bleeding at the height ofestrus was long a source of confusion between the estrous and menstrual cycles. 1 ifiwever, the two arc clearly distinguished by the fact that the female is receptive throughout the menstrual cycle (a circum¬ stance which, Sir Gavin dc beer proposed, played an important part in the social evolution of the one-to-one pairing of male and female, monogamy). cvc] it:

SEXUALITY The teleology' of sexuality is not in dispute: it provides for ge¬ netic recombination, and in turn for evolutionary versatility, by enormously enlarging the candidature Tor natural selection. Compared with the rival attractions of parthenogenesis and asex¬ ual reproduction, sexuality is clearly a Good Thing but that, of course, is not explanation enough of its having evolved. Genetic recombination is a very ancient biological stratagem that must have existed long before the evolution of sex. Bacteria have sexuality, but. some have also ihc power doubtless related to the existence of a D>JA repair mechanism to "infect” each other with their indigenous DNA, as shown by the discoveries r>r Grillith and Avery that we have elsewhere recounted. Once es¬ tablished in the population, sexual dimorphism is enforced by the chromosomal mechanism described in the definition of SEX riF,-

—

—

TF,R Ml NATION.

11 is difficult lo think of any evolutionary process other than group selection that could account for the maintenance of sexual¬ in compel it ion wilh ostensibly simpler reproductive mecha¬ nisms. Still, as John Maynard Smith says in The Evolution of Sex

ity

238

SLCKLE’CF.LL ANEMIA

(Cambridge, 1978), “even if we accept that group selection has played a significant role in maintaining sexual reproduction, it cannot have contributed importantly to the origins ofsex; nor can it be important in determining the crossover frequency and re¬ combination rales,”

SICKLE-CELL ANEMIA

Hemoglobin S is an abnormal variant of hemoglobin A: per¬ sons heterozygous for hemoglobin S, having the constitution AS, suffer from a mildly disabling condition known as sickle-cell trait, in which the red cells give the appearance of collapsing into a crescent shape: or of adopting other abnormal shapes under con¬ ditions of dcoxygenation. Approximately a quarter of the progeny of parents both afflicted by sickle-cell trait will be homozygotes with the makeup SS, These are victims of sickle-cell anemia, a seriously disabling disease accompanied by gross abnormalities of liver and kidneys. We may well ask how it conics about that the gene coding for transformation of hemoglobin A into hemoglobin fi has not been wiped out by natural selection. The answer is profoundly interest¬ ing. The gene is prevalent in parts of the world where malaria is or %vas endemic specially West Africa and the Mediterranean basin. The gene persists because the heterozygous victim of sicklecell trait enjoys a measure of resistance to one of the severest forms of malaria, that which is caused by Plasmodium falciparum. This se¬ lective advantage is sufficient to make good the loss of the gene through death of the homozygous victims of sickle-cell anemia. We have here a classic example of polymorphism maintained by the selective advantage of a heterozygote. It provides also an admirable example of the efficacy of eupltenics, for if the environ¬ ment is BO far improved as to remove the threat of malaria, the gene coding for hemoglobin S will lose its selective advantage and over many generations will slowly disappear. Indeed, this appears to be happening in the U.S, South, The notion that improvement of the environment will necessarily lead to genetic deterioration can in this instance be seen for what it is a bogey,

—

239

S? (haeoriicai

6'

Several other examples are to be found In Thompson’s famous essay On Growth and Fern (Cambridge, 1917): two are shown here.

W The mathematics of Thompson’s little morphological adven¬ has sc sera I points of interest, but before propounding them

ture

2f>b

TRANSFORM ATJONS

f 1

1 L-

&

\

L id

\

r

1

V \

s 2

4

\ i

LL

b

v\

d4

u

3

:

H5T7

6

N paraparpf of vstf-ious crabs 1. Gtryon; 2, C’ny.Tdf.f,- 3, .SgffdtttiiJ'Aia/ 4, Ptwlnmh} i>, {i, Chorijiw;

should clarify a few technical] ties, All the principles of (hr method of tra,cvsfocnia lions can be explained with reference to a plane or two-dimensional system, and to this we shall confine ourselves. Any plane figure can be represented as a set of points, each point being a number couple representing a pair of corre¬ sponding values of two coordinates ,v and y; membership in the set is specified by an algebraic formula or function from which corre¬ sponding values of.r and y can be read. Vr'C

y&A

'l'K ANSFOKh I A I U >JVS

—

Wc might, for e* ample, devise a function >ÿ

circle (jr).

0)

This expression can be taken to mean that r LIIKI >ÿ are so related that their values will define the outline of a circle when plotted on

conventional graph paper, as shown on the left betdw, Suppose we now wish |o transform this circle into the larger circle shown on the right. There are two ways to do this: b> a change of points or by a change of coordinates (in practice, both amount to the same tiling).

/ y

/

\

V

y

L

7 x'

X

—

To rcpicscTil the transformation as a change of coordinates as a change oT space rather than as a change of points- wc must in the D’Arcy 'rhornpson manner devise a different space frame. If the new coordinates arc twice their original length, the two space frames are as shown in the diagrams. The relationships between and the new ones ]*'',_>ÿ'} are given by tile the old coordinates equations .t '

7'- 2,.

= 2v,

(2)

The consequence of this is that if we plot onr old circle formula (1) on tine new grid, we gel a circle whit four times the area of the original one. Alternatively, we may represent the tra us forma tion as a change of pot tits and keep the old I u tie tion (I) and the old 267

TKA K5 TORM ATI ( »N S

grid and simply substitute die new points jr'andÿ'so that Formula (1) now becomes

£ = circle 1 \ 21 a

(3)

if, now, equation (3) is plotted on the original grid (at the left), the result will he the same as plotting equation (3) on |he trans¬

formed grid (right). The equations (a) that are the key to this simple transformation and that map the old circle into the new one are known, from their use in cartography, as mapping functions. Even when restricted to the two-dimensional outline drawings to which D’Arcy Thompson necessarily confined his analysis, it LS possible to devise an explicit algebraic function such as (1) to deline the outline of a fish or whatever else may be the subject of the transformation; but the use of this method is in no way dependent upon the possibility of doing so. All we need to know is that an algebraic formulation is possible in principle that there can be conceived to exist a function such asjr = fisher) or y = fisha(jf), to cope with one or another of Thompson’s fishy transformations or, to cope with still another kind, y = man’s face | (.v) or y = man’s facej{jf). To these we may apply any transformation we please, the point (made especially in the entry on KOftM AND MATHEMATICS) being that although it will not normally be possible to define shape with mathematical exactitude, it is certainly possible to define change of shape mathematically. D’Arcy Thompson’s method of transformations is open to a number of objections or some weight. In the lirst place compari¬ son of adult with adult :s rather un biological, because the trans¬ formation is not one that could tyke place in real life. Ii is a pity Thompson did not have figures that would have enabled him to compare a juvenile with an adult form; but perhaps if he had done so, a second shortcoming in the method would have become increasingly apparent: the fact that his method is entirely static in character, D’Arcy Thompson essentially is comparing two stills from a cinematic film. Despite all its faults a consequence of the extreme difficult y of the project (he method of transformations docs make a valid bi-

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268

TH A NS HO JIM AT I O NS

olcgitai point: in differentiating forms, it is not always necessary to compare them point by point and detail by detail, calling at¬ tention to an enlargement here and a diminution (here, u broad¬ ening in one place and a narrowing in another. It may be that we can envisage the transformation as the consequence of one com¬ prehensive morphogenetic process, such as might be the work of a single gent. This important and illuminating conception is Thompson’s real contribution lo morphology, Unless the method is to remain completely sterile, it must bit pul into motion it must be made kinetic instead of static: and in particular it must be applied to development, or at least to a sequence cT evolutionary changes. Change of shape must be rep¬ resented as a function oT age or secular time. The mapping func¬ tions are the key; and the principle of the method is to gear the transformations by parameters that vary in dependence on time, whether geological or developmental. If we slay with the simple example shown on page 267, we must first express the mapping functions (2) in a more general Torm:

—

—

x' = M*))

y = *a00-

(+)

Given the mapping Functions, It is clear that the values of the two parameters A:1 and T, determine the form the transformations take (that is, the exact degree of enlargement or—if the degree oT magnification in the two dimensions is not the same the degree of distortion to the shape of, for example, an ellipse), The key to putting the transformation into motion and con¬ verting these lantern slides intu a cinema film lies in the mapping functions (4): as we have said, the parameters must be deemed to be variable and to vary in dependence upon time, We may write therefore:

—

*L -/.{ aft n £.kirtjfa-di inhibit ii in

Allan Luis, I It). 123 123 Alleles. L 17: defined, ltd III. and

clinitaljiff Fclickk; spilofSS OCOUSj ]5

A«i ir arid, (.2 Acetylcholine, 22 23, 192. ,W

«/ÿ.« Ami-

cholinesterases

roccsstvencsii,

M2 1 13; jiiiiuriiin and, L'2U Ailclmtii a i ill ie. del i tied, 1 1 1 Allergic*, 9-10, 24, 36, GO, 155 A I k iitt tl i s, 122, 123. 131, 136, 270 271 Alloiiirtric growl he It) ]i Altruism, 1 L L3, 1 7 1 . 2 HI. $ti qita bn cinhiology A tn, ii eiiis, in science mid philucum, 74, t20, 144, 1 50, 210 24 1 Aurtfinurie, ] 1>!> Amino acids, E2, !)2, [13, 194 195, 209 A.mmniiki., 74 Anrnincemicsi*, 73. Ill, 125 Amnion. I E t Atnuebas, 222, 258 Amphibians, 119, L21, 2.72, 254 Am phlox ns, 13- 14, 1114, 325 Anabiosis, H, 362 263 Anal M2 LSI ip 3 Analogy, 145 Anajhkylad ic shuck, 10, 80 Anaplasia, 17-48 . 'ni.miiiiy, r rjdu|i:sriirivu, 40, 00 61, 145 Anenccpllnly, 14-15, 34-1 i

Aclm 1 1 d rof ibis in . I ft

ACTHj set Adremjeojticolrdjihin Aciiffi invnutiiiy, 153 A it Xjfr CtealiiM \ K< ies L k:r ) , M2 Aotiwial fiK'jiMirr-ini'iti nf aging* 5

(i

ndapiation: SHMHV, 1, 333; irritability hud, 104, 235; mimicry as, IB4 IBS, 193. See aka Conÿiilljl disorders:; Evolution jmd evolution ary theory; Fitnni; lintiiLnnihiglr pnocsio; Nalure, errors of Addison's disease, 132 Adenovirus- 12, 187, 220 Adrenal gland, 2-3. 65, 76. 7J-78, 79-60

AdKnal ire, 2 Ad ty;nr hfvu’t ifi a p L i] hh i i h (ACTTH), 3 Africa, 36 Afla A (ant i>n),

57-58. 197 Menopause, ft Menstrual cycles, 44. 141, 437-433

Menial retardation, .iff Congenital dis¬ orders Mcriean-Ponti, Maurice, 184 Mcsclson, Matthew, 189 Mesoderm, 7fi, 79, [30 Mcsoi helium, 79

Mesozoic |>eriod. 131 Metabolism biospheric, 74; thyroid and, 70; ettzyiives and, 78-79; dc-

fined, 1154; diaphragm and, 190;

thermoregulation amt, 458-459 Metamorphosis, 1 19; ncolcny and, 199 400 Metaphysics. 4 7 Mctaphylcs, 70 Metastasis, 46 Meta theories, 140 Metazoans, 70 .71. 1 0:1 Meteorites, 4014 Meteorology. 74 Meliric, Jo!ten Offroy tie la. 181 Methotrexate, 49 Micellae, 114 Microscopy. 77, 78. nu-s; Dt-oxyiihounckir acid; Uihnnucictc acid Nucleotides, 202, 219-220

Mules, 191

Muller, Johannes, 164, 235 Mullerian mimicry, ISM Mullet, 26 Multiple sclerosis, 155 M Lira title acid, 251 Muscle, skeletal: adrenaline and, 2; steroids and, 3, a lit icholinesl erases and, 22-23. tin atm Myasthenia gravis Mushrooms, 264 Mussels, I 19, 189 Mu union. 111, 115, 155; in cxusornatic evolution, 5)(? 97; defined, 120-321; group sclcctkitl and, 154 L35; impar¬ lance in rvolulkiil, 198, tin aim Con¬ genital disorders; Genetics; l„iniarckism Myasthenia gravis, 23,64, 155, 191192 Myocardium, 01 62 Myoglobin, 187, 220 Mythology; classical, 54; NUIM-, 63. See alto Creationism; Eugenics; Trttllt

Objective Kmetletige (Popper), 97 Oceans, 71 Ochoa, Severn, 189

National Institute for Medical Re¬ search (J»ndon), 2(>2 Natural selection, lOO- 101, 115, 117, 193, 1116; pressure of, 4(i, 119; of groups, 134-135, 2341-239; imporlaitcc in evolution, 198. Steals" Eugenics; Evolution and evolution¬ ary theory; Fitness; Siockbuccding Nnl u ie : errors of, 71, 79 82; vs. nurture, 108. 109, 127-128, 194 196. Set aha Allergies; Congenital disorders; Otneiics; Punglossism: Tokology Nauplii, 33 Nematodes, 163

Neateetsieteim , 175 Non- Darwinism, 134, 167, 196—199 NeustigiriitlC, 23, 63 64 Neuteny, 199 200 Nerve gases, 200 Nervous system: sensory adaptation and, 1, 235-237; sytn pathetic, 2, 73, 24K 2541; rtf arthropods, 30; of print!•

Octopuses, 1IKJ OII’IL iy de la Mellrie, Jutien, 1 43 1 Oncology , see Cancer

Onions. G. T„ 193 Ontogeny, 121. See al.w Recapitulation Oulogtnf /tent {‘iiyhÿnly fConld), 227 t>nychophura. 30 ( Xu vies, 1 2 1 - 122. See also Eggs and chickens; Ca metes; Reproduction

Oparin,

Often

Aleksandr, 2(18 Iti Enemies, The (Ptip-

Stately taai

JMT), 145 Oral i gut ails, 24. ISO Order in biology, 204-207. Set atm Randomness; Taxonomy Orders of magnitude, 207-208 Organ transplants, 17,66-67,80, 122

Orgel, 1 j;sJie, li Origin ajSpeeits, The (Darwin), 81. 186

298

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.13 S3 , 181-185 Schlcide tt, Matthias, 51 Sc h 11 H lm grr , Erwin, 511-59, ill, 205,

296 Schumann, Robert, 129 Schwann, I bend or, 31 Seine:*: unrf Phifoiofthi uf i/ir Org amsm , n>f (Dricseh), 276 Seiencc and scientists: Anslnlle as pom model, 2(i-29: scientific method and, 43, 75, I 18 15 1; metaphysical specu¬ lation as source of ideas, 17; arnatetus. 74. 120, (50, 240 241; evidence and, 92- JH; frauds, 107 Lf JH, 157. 214-215, 2G1; resistance in change. 132; paradigms, 1 19; specialization. 189. Mrr uho Biology and biologists; (In-al inuisin; Demography and de¬ mographers; Ecology; Envircmmcntalisis; Ethology; Physics and physi¬ cists; Psychology anti psychologists;

Veterinarians Seiencc liction, 59-60 Scimiiijii Basis of Ei'elulioir, itu (Mor¬ gan). 95, i 10 Scientism. 44. Set itlso Port ism Scopes, Joint T . trial, 02 Scum-, 377 ,Vty 7omulhiti, '2fifi Sea anemones, 237 Sea cow1, Srrllrr’s, 19 Sea cucumber*, 161 Sea lilies, 237 Sea linns. 232-253 Seals, 252-253. 280 28) Sea squirts, 13, 14, 119, 199-200 Sea urchins, 1 19, Hi I, 211, 276 4.t- 1 1 Scgnienlalion, 30 Segregation, law of, 118, 119. 124 Selection pressure, It), 119 Self-fertilization. I 18. 237 Sttfuli Gent. 7/tc (Hawkins), 241 Semantics, 1 19 Seneca, 120

301

IXUI'LX

Senescence, 4 8, 144 I4h. Htt aha

GrtWth, law* nflmilogicrt! Sen*atkÿit adaptation and, l, 235; orgSji* of, 234 237 wwt Seustbtiit/ (Ausicn), 34 Serve! ui. 43 Serum. bipod, 42, 154 animal;, 33, 112, 119, 122, 147, 237 Scw-i-lf, Arina, H>

Sc* (gender); cancer Hind, 49; gynandtOtllDf pittite) arid, 33; dckTHiiiiu38, I SI, 124 L2C Sex ratios, 125-126 ScxuaJ etyeileÿc, itt liatrouf cycle*; McnsTftiijtt cycles Sexual desire, 1 32 Sexual development, 7(1; rieoteuy anti, I 99-200 Sexual i l V 238-239 Sexual rivalry, 4 SliaJcchpearc, William, 124

lior|

ShfirpcV’Sliafer, Ktlwaid. 249

ShaVf, Ceorge Bernard. Sheep; (ii

133, 166,

270

Shelley, Percy Bysshe, 213 Shcriiiglnji, Charles, 233 ShJykuv, (i. IS'., ]7H shuck, imaphylad ty, 10 Siamese twins, 127, 237 Sib*.. 122, p6. Sa afa1 Inbreeding Sickle-cell anemia, 52. 82, 92, 123, 239 Sidney, Philip, 28 Skin: allergic cdt-rm :i t it is and, 9; :d hi¬ ll Lsm and, 9 10; healing til' yvonnds; 41-42; grafting, 42, 154, 211, 270-271; tumors, 43. 49; ibernumÿ illation and, 2411-247,238-259; toughness, 282 Skinner. E. 1., 232 Sleep, 147 Shy fling sickness, 223

189, 190 Smallpox, 273 Smith, K. A., 1 89 Smith, J- A., 27

Smith, John Maynard, 12. S38-239, 256 Smoking, and lung cancel1, 40, 84 SniiJti. Jan -Christ iaa it, 144 Snails, 189

Snakes, &4 Social Ein!rdni/i iKiddl, 2-11 Socialists, -I, 34, 143-1 44J '2.i 7. Her u/.wi Mariinm Politics arid political AysLem;

Social nrgmiÿlion: i>f apes : 1 |]; individualism and. 137-158, -Stt ahv Ethology SÿjtLcr y lor the Prevention of Cruelly lea Animals, Id

Suci-ohiolqgy, 24ll-24li tin select iotl in, II 1 2; ideology in, 256 SafwWWggy {Wilson), 240

-

IfccfolitlgiitAiicN, 241 JWrckilogy: ll isi 1 ii ici sit 1

in, L-13; u-dLLCikiilitm and, 22E, 2140: egreippii:; icirriihology, 258 Sodium; fir Salt reguiat inn 7H 1 1 i F hjirima, 2! I SonYa;: separation Ihim germ pbsitdl 53-34, 242; influent* of psyfitlc, [33, 242-2-!4 Sc mi It America, 4t> Soviet Uniop iH'rfl- 167, |7ii ITS, 245 Special creation doctrine, n-r Creation[MJ'I

Species, in

taxortoEity, 253*-i2_5_5

Specificity, 24 i 96, LOO, 24 L Spencer, Sfie'rl it 1 eff-r, 1 Javld, L 7 Sperm. 114, 12L 123, 133 Spina hiliHit, 14 13, 2-M. 256-251

Hfrtoen,

Spirit, posture and, IK I HI Spiny antcalen, 185, 191 Spirochetes, 224, 230, 23 L Spoil luiieou* genera!iuu. 243-246

SfMttiuiwrilt* {/rrifftttiwt /JrVfljtci lo Djuint\r Sfmreti, Ill, 24(j

Tkf

fnJUT fPifricYju 24 1 i

SPOITIUA, 223 Squids, LOO Stalin, Josef, 1 77 Staphylococd, !H, 133 Starfish, 164 Sid HIT, Jacufj, 103 Stephen, Ixdie, 241 Steroids, 2-3, 10 Stewardship, 13-20, 79-80, 182-183, 191

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