DARWIN AND HIS CRITICS

The Receptionof Darwin's Theory of Euoluti,on by the ScientificCommunity

DAVID L.. HULL

The University of ChicagoPress

Chicago and London t"fr mf vfü{".!4q48

The University of Chicago Press,Chicago 60637 DEDICATED IN APPRECIATION TO The University of ChicagoPress, Ltd., Lon-don Virginia and Glenn D. Bouseman @ 1973by David L. HuIl All rights resewed. Published l97B Iris and Robert H. Reid University of ChicagoPress edition 1983 Printed in the United Statesof America

90 89 88 87 86 2345

Library of Congress Cataloging in Publication Data

Hull, David L. Darwin and his critics.

Reprint. Originally published: Cambridge, Mass.: Harvard University Press,1973. Bibliography: p' ' Includes index. l. Darwin, Charles,1809*1882, On the origin o{ species. 2. Darwin, Charles, 1809-1882.The descent o[ man. 3. Evolution. I. Title. QH365.08H84 1983 575.0r'62 83-4855 rsBN 0-226-36046-6

89 , / B50Q Preface produce the finished version of the von Baer paper. wayne Gailis offered numerous. suggestionsfor improving the translation of pictet's essay.Kather- ine Kirkish, Dawn Klemme and Dorothy Dietrich labored to type and retype the lengthy manuscript. This anthology was prepared under National ScienceFoundation Grants GS-1971 and GS-3102.

D.L.H. Contents

I Introductory

Chapter I.. Introduction . 3 Chapter II. The Inductive Method 16 Chapter III. Occult Qualities 37 Chapter IV. Teleology JJ Chapter V. Essences ot

II eviews

ol JosephDalton Hooker (1817-1911) UT WilliamBenjamin Carpenter ( 1813-1885) 87 H. G. Bronn( 1800-1862) 118 ThomasVemon Wollaston ( I 821-1 Bi8 ) 126 FrangoisJules Pictet (1809-1872) L+2 AdamSedgwick ( 1785-1873) 155 111 RichardOwen ( 1804-1892) LI L SamuelHaughton ( 1821-1897) 216 WilliamHopkins ( 1793-1 866 ) 229 HenryFawcett ( 1833-1884) zto FrederickWollaston Hutton ( I 836-1905) 292 FleemingJenkin ( 1833-1 885 ) 302 Contents

St. George Mivart Jackson ( 1827_1900 ) and ChauncyWright ( 1830_t 875 ) J3 l Karl Ernstvon Baer (l7g}_l}7 6) itlo Louis Agassiz( 1807-1 873 ) 428

Conclusion 450 Bibliography +59 trntroductory Index +69 Introduction

Darwin expected theologians, people untrained in scientific investigation, This leads me to remark that I have always been treated honestly by my and even those scientists who were strongly religious to object violently reviewers, passing over those without scientific knowleirge as not worthy of to his theory of evolution. He had also anticipated the skepticism of even notice. My views have often been grossly misrepresented, bitterly opposed and the most dispassionate scientists. He had not Iabored over twenty years ridiculed, but this has been generally done, as I believe, i'gooä faith.- for nothing gathering facts to support his theory and attempting to discount Charies Darwin, Autobiography, p. l2S. those that apparently conflicted with it. But he had not anticipated the vehemence with which even I have got fairly sick the most respected scientists and philosophers of hostile reviews. Nevertheless, they have been of in his day would denounce his efforts as not being use in showing me when properly "scientific." to expatiate a little and to introduce a few new discussions. To the extent that these latter reactions were genuine and not the result of religious bigotry, they can be explained I entirely agree with by reference to the philosophies you, that the difficulties on my notions are terrific, yet oT science popular in Darwin's day. In this chapter Darwin's understanding having seen what arl the Reviews have said against me, r have far more of the philosophies confidence in of science of his day and his own. views on science the generar truth of the doctrine than r formerly had.-charres will be set out as fully as possible. Darwin to T. H. Huxley, Down, December 2, 1860, Lit'e and.Letters,2:147. Darwin had both the good fortune and the misfortune to begin his scien- tific career at precisely that moment in history when philosophy of science came into its own in England. Of course, philosophers from plato and Aristotle had always written on epistemology and, after the scientific revolu- tion, they were presented with the added advantage and obligation of recori- ciling their philosophies with the current state of science. some of these philosophers were also themselves scientists. But the works of Descartes, Locke, Hume, Berkeley, Leibnitz, and Kant do not exhibit the same concern with the accomplishments of science and the nature of the .,scientific method" which has come to characterize philosophy of science.l

i. I an not want to exaggeratethe differencebetween epistemology and philosophy of science.I have no serious quarrel with those who want to identify the rwo, as doesGerd Buchdahl(1969). However,r am primarily interesredin thl reception of-evolutionarytheory by scientistsin the niniteenth century. For this pr.ior., I have chosento narrow the focus of my discussionto those areas of epistem"togy which seem most closely connected to the scientific enterprisc. Darwin and His Critics Introduction

all alvare of its shortcomings. Commencing with John Herschel's Preliminary Discourse on tha Study out above, Flerschel, Whewell, and Mill were of Natural Philosoplty (1830), English-speaking scientistsbecame self-con- Science had not and could not proceed by the method set out by Bacon. scious about the proper method of doing science. During the years Yet Bacon was the patron saint of the scientific revolution, and "inductive" 1837-1842, when Darwin was residing in London and rvorking on the species was an honorific title not to be discarded' lightly' Al1 three men wanted problem, the great debate on the philosophy of science erupted between to reservethe term "induction" for the processby which scientific knowledge. wanted to use it to refer to the means William Whewell (1794*1866) and John Stuart Mill (1806-1873). In 1833 is attained. Simultaneously they also Whewell contributed his Astronomy and General Physics Considered witlt by which such knowledge was proved {actual. For Herschel and Mill induc- the reference to Natural Theology to the Bridgewater Treatises. In 1837 he tion was the discovery of empirical laws in the facts, reasoning from the published his History of the Inductiue Sciencesand in 1840 The Philosophy known to the unknown. Concurrently, this inductive method insured of con- of Inductiue Sciences,Founded upon their History. Darwin was impressed truth of these laws. For Whewell, induction was the superinducing to by the breadth of lOn the Origin of Species Races in the struggle (1561-1626) to contrast his abortive "inductive method" with the Aris- ol Natural selection, or tlte Preseruation of Fauoured coincidence was' to say the least, a totelian "deductive method." As popularly misconceived, the deductive for Life (1859). For Darwin, this method consistedin an irresponsibleleap to a conclusion of high generality mixed blessing. Discourse which, and the subsequentdeduction of consequencesof these generalizations re- In his last year at cambridge, Darwin read I{erschel',s in him"a burn- gardlessof observedfacts. Perhaps the scholasticsat their worst were guilty along with I{umboldt,s PersonalNarratiue (1818), stirred the noble structure of such maneuvers, but the above characterization was not only a parody ing zeal to add even the most humble contribution to eticit precisely this of Aristotle but also fails to identify the actual weaknessesin Aristotle's of Natural Science."3Herschel had written his book to scientific revolution. system. The inductive method, also as popularly misconceived, began with reaction in his readers.Newton had brought about the the details of Newton's observation and proceeded by the cautious construction of generalizations Henceforth, all scientists had to do was to filI in always within the New- of greater and greater generality. The deductive method proceeded from great structure, perhaps expanding upon it, but science and reiigion' the peak of the pyramid of knowledge down to its base,whereas the induc- tonian framework. Nor was there any conflict between o{ the Bible, but scientists tive method started at the base and worked up. The superiority of a pyramid Geology had challenged the literal interpretation concern themselves resting on its baserather than its peak was obvious. and theologians had made their peace. scientists could but the first cre- Although Bacon carne close to advocating the inductive method as set with the workings of the material world, once created, 2. Darwin (1958),p. 66. 3. Darwin (1958),p. 67. Darwin and His Critics Introduction

ation, 'life, mind and soul were the province of the theologian. "To but he was not prepared for the criticism which his methodology was to ascend to the origin of things, and to speculate on the creation, is not receive from the most respectedphilosophers and scientistsof his day. Most the businessof the natural philosopher."a Not only were scientistsmaliing contemporary commentators tend to dismiss these criticisms as facile, disin- great contributions to the noble edifice of science and to mankind by genuous and superficial, suspectingthat they stemmed more from a distaste applications of science in medicine and industry, but their discoveriesalso of the content of Darwin's theory than from his methodology, but this lent support to religion through natural theology. As they discovered more dismissal is itself too facile. Certainly the repeated invocation of the clearly how nature worked, they showed how great the creator's wisdom Baconian method by many of Darwin's critics and even by Darwin himself had been. In his youth Darwin had hoped to join in this great parade indicated no great understanding of the actual nature of this method or of scientists and men of God marching arm in arm to produce a better the philosophy from which it stemmed, but the leading philosophers con- world. Instead he stopped it dead in its tracks. temporary with Darwin, John Herschel, William Whewell, and John Stuart In his early publications, Darwin gave every appearance of contributing Miil, were equally adamant in their conviction that the Origin of Species his share to received science. His journals concerning the voyage of the was just one mass of conjecture. Darwin had proved nothing! From a Beagle were in the best tradition of such narratives. FIis monographs on philosophical point of view, evolutionary theory was sorely deficient. Even living and fossil barnacles certainly were in no way controversial. Even today, both Darwin's original efforts .and more recent reformulations are the publication of his papers on the formation of the Parallel Roads of repeatedly found philosophically objectionable.GEvolutionary theory seems Glen Roy (1839) and of coral reefs (1842), though theoretical in nature, capable of offending almost everyone. did not detract lrom ]ris growing reputation as a true inductive scientist. In the first, he expiained the appearance of a series of parallel shelveson In the nineteenth centur-y, "to be scientific" meant to be like John the sides of a glen in Scotland in terms of the gradual elevation of the I-Ierschel'sextension of physical astronomy to the sidereal legions.T Thus, land. The parallei roads were actually the remnants of former beaches. Darwin was especially anxious to heal the opinion of Herschel, the "great In the second, he explained the forrnation of coral reefs in terms of the philosopher" referred to in the opening paragraph ol the Origin He sent gradual subsidence of the ocean floor. New coral grew on the old as it Herschel a copy of his bool< and wrote to Lyell to pass on any comments feii beneath the surface of the warer. But with the publication of the Origin which the great physicist might make since "I should excessivelylike to oI Species,large segmentsof the scientific and intellectual community, hear whether I produce any effect on.such a mind."8 Herschel's opinion turned on him. Both Adam Sedgwick, the eminent geologist, and Richard was rapidly forthcoming. Darwin wrote to Lyell, "I have heard, by a round- Owen, the leading comparative anatomist of the day, had encouraged Dar- about channel, that Herschel saysmy book 'is the law of higgeldy-piggeldy.' win in his early work. After the Origin, their praise turned to ridicule. What this exactly means I do not know, but it is evidently very contemptu- Sedgwick (1860) complained that Darwin had "departed from the true ous. If true this is a great blow and discouragement."e In the face of inductive track." Owen, while admitting that he himself had casually enter- such a rejection by the most eminent philosopher-scientistof the century, tained the notion of natural selection,had judiciously refrained from enun- it is easy to understand Darwin's pleasure when he discovered in an equally ciating it. It was "just one of those obvious possibilities that might float roundabout way that another great philosopher, John Stuart Mill, thought through the imagination of any speculative naturalist; only the sober that his reasoning ln the Origin was "in the most exact accordance with searcher after truth would prefer a blamelesssilence to sending the proposi- the strict principles of logic."lo On closer examination, however, Mil.l's tion forth as explanatory of the origin of species, without its inductive 6. See,for example,Woodger (1929), Kneale (1949), von Bertalantry(1952), foundations."s Grene (1958),Himmelfarb (1959), Manser (1965), and Mooreheadand Kaplan (1e67). Darwin was prepared for the abuse which the content of his theory, 7. Cannon(1961), p. 238. especially its implications for man, was to receive from certain quarters, 8. Darwin,November 23, 1859,Lif e andLetters (1887),2:26. 9. Darwin,December 12, 1859,ibid., 2:37. 4. Herschel(1830), p. 38. 10.Darwin, Henry Fawcett to C. Darwin,January 16, 1861,More Letters(1903), 5. Owen (1860). 1:189. Dalwin and His Critics Introduction

endorsement can be seen to be not nearly reassuring. Darwin had prop_ the logical order of a reconstruction of scientific method. According to erly used the Method of Hypothesis, but this rnethod belonged to the logic empiricist epistemology,all knowledge has its foundation in experience.This of discovery, not proof. In spite of twenty years' labor, Darwin hacl failed tenet was mistakenly taken to imply that a1l scientific investigation has to provide proof for his theory of evolution by natural selection. to begin with observation. The true inductive scientist began collecting Darwin's own views on the nature of science exhibited the conflicts and data indiscriminately, with no preconceived ideas, and gradually evolved ,,hy- inconsistenciestypical of his day. He evidencecl the usual distrust of broader and broader generalizations.The process of scientific investigation potheses" while grudgingly admitting their necessity.For example, in a assured both the truth and the empirical meaningfulness of the resultant letter to I{ooker, Darwin claimed that he looked upon "a strong tendency propositions. Deductivists approached nature with a hypothesis already in to generalize as an entire evil"11 and yet admitted in his Autobiography: mind, and speculators flew too quickly to generalizations of too great a "f cannot resist fo'ning one on every subject.,'l2 In the opening paragraph scope. Thus, Darwin can be found saying of his coral reef paper, 'oNo of the Origin of SpeciesDarwin sketched the following history of the devel- other worl< of mine was begun in so deductive a spirit as this; for the opment of his theory: whole theory was thought out on the west coast of S. America before I had seen a rue coral reef."lo Similarly with respect to his theory of When on board H.M.S. "Beagle," as naturalist, I was much struck evolution, he conceded to Asa Gray, "What you hint at generally is very, with certain facts in the distribution of the inhabitants of south America, and_in the geological relations of the present to the past inhabitants very true: that my work will be grieiriously hypothetical, and large parts of that continent. These facts seemed to me to throw some lieht on by no means worthy of being called induction, my commonest error being the origin of species-that mystery of mysteries, as it has been called probably induction from too few facts."15 by one of our greatest philosophers. On my return home, it occurred In a letter to FIenry Fawcett, however, Darwin indicated that he realized to me, in 1837, that something might perhaps be made out on this ques_ that data cannot be gathered efficiently without some hypothesis in mind: tion by patiently accumulating and reflecting on all sorts of facts wirich could possibly have any bearing on it. Afte; five years, work I allowed About thirty years ago there was much talk that geologistsought only "to myself to speculate on the subject, and drew up some short notes; these observe and not to theorize; and I well remember someone saying I enlarged in lB44 into a sketch of the concluiions, which then seemecl that at this rate a man might as well go into a gravel-pit and count to me probable: from that period to the present day I have steadily the pebbles and describe the colours. FIow odd it is that anyone should pursuedthe sameobject (p. 1). not see that all observation must be for or aeainst some view if it is to be of any service!t6 rn his Autobiography Darwin recalls roughly this same sequenceof events but adds that he "worked on true Baconian principles and without a'y What mattered was that the hypothesis be an empirical hypothesis, one theory collected facts on a wholesale scale."t3 But Darwin was well aware that could be verified or refuted by observation, and that serious attemPts that the possibility of speciesevolving had occurred to him soon after his be made to gather the relevant data. Immediately after saying that his return from his voyage on the Beagte (if not before) and his principle coral reef paper was begun in a deductive manner, Darwin adds, "I had of natural selection not much later, in october 1838. Five years may have therefore only to verify and extend my views by a careful examination elapsed before he permitted himself to write an essayon the subject, but of coral reefs."l7 Darwin's own experience as a scientist forced him to he had speculated and collected facts in the iight of these speculations recognize that the order in which hypotheseswere formed and the relevant from the very first. data gathered was not rigidly set. It helped to have a hypothesis in mind, The source of this fabricatio' is easy to uncover. one of the most preva- but hypotheses had to be changed as the investigation proceeded.ls His lent confusions in the work of even the best scientists and philosophers theory of the formation of coral reefswas formulated before he had collected was between the temporal order of an actual scientific investigation and 14. Ibid.,p. 98. 15.Darwin, November 29, 1859, More Letters (1903), 1:126. l. 1 Darwin, January11, 1844,More Letters( 1903) , 1: 39. 16. Darwin,September 18, 1861, ibid., l:195. 12.Darwin (1958),p. 1al. 17.Darwin (1958),p.98. 13.Damin (195S),p. 119. iB. Ibid.,p. 14i. t0 Dalwin and His Critics Introduction 1l

very much of the relevant data and turned out to be largely factual. I{is chided him for objecting to the skepticism of scientific men. "You would theory of evolution by natural selection was formulated after several years not fulminate quite so much if you had had so many wild-goose chases of observationsas a naturalist, followed by two decadesof additional, selec- after facts stated by men not trained in scientific accuracy."2o tive investigation, and it too was basically correct. I{is theory of the Parallel Darwin's conservative views on publication were rewarded to some de- Roads of Glen Roy had much the same history on a smailer scale as his gree. His Origin ot' Species did not suffer the same fate as those works theory of evolution, but was mistaken. In the case of inheritance, Darwin on evolution that had preceded it. It was treatecl as a serious work of actually did amass facts wholesale before he succeeded in working out science even by those who denounced it. But a similar reticence on the his theory of pangenesis.Its {ate was even more unhappy than that of part of Gregor Mendel resulted in his laws of heredity being overlooked the Parallel Roads theory. Clearly there was no connection between the for almost forty years. Mendel published his laws in 1865, soon after the temporal order of fact-gathering and hypothesizing and the truth of the appearance of the Origin He too wanted to avoid being branded a specu- hypothesis. lator. In his original paper he barely alludes to his unobservable "factors," Ilowever, Darwin did think that the temporal order of the verification though the cogency of his entire argument rested upon their existence. and the publishing of a hypothesiswas important in the sociologyof science, In a letter to Carl Nägeli (X{endel, 1867), he claimed that, "as an empirical both for the salmeteorology.He felt that the originality of his impressionisticsketches would sciencesby the prevalence of deductive reasoning in the for"mer. Of Spencer, be enough to rnotivate others to undertake the subordinate task of filling Darwin complained: out and verifying his theories. As Burkhardt (1970) has aptly observed, His deductive manner of treating any subject is wholly opposed to public neglect and private ridicule were the late of his theories. prior ro my frame of mind. I{is conclusions never convince me; and over and knowing that chambers was the author of the vestiges of creation, Darwin over again I have said to myself, after reading one of his discussions,- 20. Darwin,April 30, 1861,More Letters(1903),2:443; see also, Darwin (1871), 19.Darwin, 1863, More Letters(1g03), 2:323. p. 606. 12 Darwin and His Critics Intloduction IJ

"Here would be a fine subject for half-a-dozen years' work." Ilis funda- he seldom was presented with a situation in which he could use such deduc- mentai generalizations (which have been compared in importance by tive reasoning. He .was constantly forced to deal in probabilities, and no some personswith Newton's Laws ! which I daresaymay be very valuable ) one could tell him how to compute and combine such probabilities. I{e under a philosophical point of view, are of such a nature that they agreed with Lyel1 about "mathematicians not being better able to judge do not seem to me to be of any strictly scientific use. They partalgeologists ought to be trusting mathematicians."2a And in his autobiography he saysof his theory of par.rgenesis: Darwin could not help but know the crucial role which mathematics Towards the end of the work I give my well-abused hypothesis of had played in physics, since Hersihel had repeatedly emphasized it in his pangenesis.An unverified hypothesisis of little or no value. But if anyone Discourse,.but it did not seem to be in the least useful in his own work should hereafter be led to make observations by which some such hy- in biology. On occasion he had to make some simple computations. When pothesis could be established,I shall have done good service, as an aston- these proved too much for l.rim, he asked for help. In later life his son ishing number of isolated facts can thus be connected together and ren- dered intelligible.20 Francis took over this duty. What seemed to bother Darwin was that the kind of mathematical techniques he needed most were not available. For Darwin produced several theoretical works in his career: two were in Darwin, mathematics consisted of deductive reasouing, and he distrusted error (pangenesisand his explanation of the Parallel Roads of Glen Roy) greatly "deductive reasoning in the mixed sciences." In his own work, 25. Dar-win,June 17, 1860, ibid., 1:154. For severalamusing anecdotes about Darwin's mathematical ineptnesssee Himmelfarb (1959). 21. Darwin (1958),p. 109; seealso letter to J. Fiske,December 8, 1874,Life 26: For a further discussion see the comments to the reviews of Haughton and and Letters(1887), 2:371. Fawcett. 22. Darwin,March 4, 1850,More Letters (1903), 2:133. 27. DeBeer (1960), 3:142. 23. Darwin,April 15,1872, ibid., 1 :336. 28. Darwin, April 23, |BGL,Life and Letters ( 1887), 2: 155. 24. J)arwin,August 7, 1869,More Letters (1903), l:315. 29. Darwin (1958), p. 120. 14 Darwin and I-Iis Clitics Intloduction 15

and two correct (evolutionary theory and his explanation of the formation book that scientifrc revolutions are so traumatic that no reasons can be of coral reefs).30 His procedures in formulating. articulating, and verifying given for preferring one theory to another. Either one accepts the old these theories and explar-rationswere roughly the same, yet no one com- theoly and its standards of rneaningfulness and truth or the new theory plained of the methodology of l.risGlen Roy or coral reefs papers. If Dar- and its differing standards. The transition is almost mystical. Needless to win's methodology was faulty in the Origin, then it should have been equally say, considerable controversy has followed upon l{uhn's reconstruction of faulty in all of his scientific works. scientific revolutions as fundamentally arational processes.llowever, all of' What was wrong with Darwin's theories? Was his methodology faulty? the discussions in this dispute have centered on revolutions in physical What is the nature of inductive formulation and proof which eluded Dar- theory. The revolutions in biology have been al1 but ignored.3l The essays win? These are the questions which occur to the modern reader when in this anthology should provide arnple source material for the disputants first confronted by the reviews of the Origin of Speciesand Darwin's later on the valious sidesof this controversy. work, especially the Descent of Man. Some of the reviewers were obviously In Chapter 2 the logic of justification ar.rdits relation to discovery will biased. Some were merely mouthing undigested platitudes. But many of be examined. What did it take ro proue a scientific theory? Why had the reviewers were competent scientistshonestly trying to evaluate a novel Newton's theory supposedly fulfilled the requirements of proof while Dar- theory against tl-re commonly accepted standards o{ scientific excellence, win's failed? In Chapter 3 the problems,surrounding concept formation and evolutionary theory consistently came up wanting. The solution to and meaning will be discussed.Early scientists were deeply impressed bv these puzzles can be found ir-r the philosophies of science promulgated by the failure of Aristotelian science in the hands of the Scholastics. They such philosophersas I{erschel, Whewell, and Mill and their most important identified this failure rvitl'r the "deductive method" and with the central predecessors,Aristotle, Bacon, and Newton. Darwin was caught in the rnid- role of "occult qualities" in ear'ly scientific theories. The fear of occult dle of a great debate over some of the most fundamental issues in the qualities was so strong in many scientiststhat any reference to unobservables philosophy of science-the difference between deduction and induction and was looked upon with extreme suspicion.But coexisting with this hard-nosed the role of each in science,the difference between concept formation and empiricism was an equally strong belief in God as an underlying first cause the discovery of scientific laws, the lelation between the logic of discovery and his occasional dilect intervention in natural processes.This schizo- and the logic of justification, the nature of mathematical axioms and their phrenic attitude of scientistsproved to be one of the strongest impediments relation to experience,the distinction between occult qualities and theoreti- to the acceptance of evolutionary theory. As I(uhn (1962) has observed: cal entities, and the role of God's direct intervention in nature. Before "For many men the abolition of that teleological kind of evolution was the philosophers of science had thoroughly sorted out these issues,they were most significant and least palatable of Darwin's suggestions.The Origin presented with an original and highly probiematic scientific theory to eval- of Speciesrecognized no goal seteither by God or nature" (p. 171). uate. That they rejected evolutionary theory, a theory which has outlasted Chapter 4 will deal with the effect that essentialismhad on the acceptance many of the theories judged to be exemplars of scientific method, says of evolutionary theory. Although this topic has been discussedextensively something about the views of science held by these philosophers and elsewhereseit is too intimately connected with the problems at issue to scientists. allow omission..Seldom in the history of ideas has a scientific theory con- flicted so openly with a metaphysical principle as did evolutionary theory In the succeedingchapters, the interconnections between Darwin's theory with the doctrine of the immutability of species.s3 of evolution and the philosophiesof scienceculrent in his day will be traced. 31. SeeRuse (1970 and 1971),Greene (1971), and Ghiselin(1971). It is hoped that this discussion will aid the reader in understanding the 32. Mayr (1959a)and Hull ( 1965). various criticisms in the ensuing reviews and in placing them in their ap- 33. The following works are recommended for further reading in the philosophies of Aristotle, ßacon, llerschel, Whewell and Mill : Blunt (1903), Ducasse (1951 propriate conceptual setting, I(uhn (1962) has argued in his influential and 1960), Anschutz (1953), Heathcote (1953), Hochberg (1953), Strong (1955), Cannon (1961), Walsh (i962), Grene (1963), and Butts (1968). 30. For a discussionof someof Darwin's other scientifictheories see Ghiselin (1969). fhe Inductive Method t7

with those of their principles. But this was not the natural history and experiencethat was wanted; far from it.t

As far as Aristotle's professed epistemology is concerned, Bacon's charac- terization is anything but fair, though it accurately depicts the level to which it frequently sank in actual practice. IJowever, in singling out Aris--. totle's emphasis on deduction at the expense of induction, Bacon failed 2 ' The Inductive Method to identify the most significant source of error in Alistotle's epistemology. In fact, deduction will continue to play a central role in scientific procedures tlrroughout the history of science.The real culprits are the quest for absolute certainty in the acquisition of knowledge and Aristotle's use of intuition rn the light of the great advances in physics in the seventeenth and to accomplish this end. Future philosophers of sciencelike Bacon, Flerschel, eighteenth centuries, nineteenth-century philosophers ancl scientistscollabo- and Mill will join Aristotle in his quest for absolute certainty but will rated to produce a philosophy of scienceconsistent with these achievements. attempt to obtain it by a strict application of inductive logic. In their informal remarlanimals. Animals are divided into additional classes they framed the art. After that, if any new particulars and examples of reduced scope, e.g., protozoans, round worms, and chordates. Each of rep.u.gnanjto their dogmas were mooted and adduced, either they sultly these classesis subdivided in turn until the lowest level is reached-species, molded them into their system by distinctions ancl explanations of their ryle3, or else coarsely got rid of them by exceptions; *frlt" to such par_ 1. Bacon(1620); bk. I- AphorismCXXV. ticulars as were not repugnant they labored to issign causesin co.rformiry 2. For example,see J. J. Bakerand G. Allen ( 1968). 1B Darwin ar-rdFIis Critics rlre Inductive Method l9 subspecies,ol valieties. At the bottom of the pyramid are arrayed individual Hcrc lhe increase in generality is obvious. The conclusion is more general organisms. tbiLn the premises taken separately or together. But there has been no When we turn to a consideraiton of statements of greater and greater lscent in the pyramid of concepts. Crows and blackness are rnentioned generality and inferences among thern, the whole idea of descending and in all the constituent statements. To use such an inductive argument one ascending in a pyramid ceasesto be appropriate. For example, the following rnust alleady l

|.l f, .f;

l I 20 Darwin and FIis Critics rhe Inductive Method 2l

and Mill attempt to eliminate it by trying to make inductive inferences small induction,s but as Aristotle's own efforts and those of his followers more rigorous, Aristotle by recourse to intuition, and whervell bv reference give ample proof, these precautions tend to be ignored in an epistemology to self-evident truth. based on the infallible intuition of immutable essences.The source of error For Aristotle, k'owledge began with the observation of individuars rike in Aristotle's epistemology is not the deductive organization of hnowledge. Callias, Socrates,Alcibiades, and Ajax and proceeded by simple enumera- After all, verification by the deduction of observational consequencesis tion until one intuited that which is universal in .them-their essence,or one of the best ways of checking the truth of a scientific law, but deduction formal cause. This process of concept formation preceded any inductive to the individual as exemplified in argument (2) has no place in Aristotelian inferences in the strict sense,since it preceded the formation of statements. epistemology.Science deals only with that which is universal, with essences. It cannot be represented as in argument (3), since in this argument one After essenceshave been genuinely intuited, checking by observation is already has the concepts, crow and black. one merery observesindividuals superfluous. and intuits their essence.For example, one might intuit that all the incli- By the time of Francis Bacon (1561-1626), the scientific revolution was viduals listed above were men, or human beings, or animals. Intuition well under way with the work of Copernicus, Galileo, Tycho Brahe, I(epler, need not begin with the lowest universal and proceed only iater to universals Gilbert, and I{arvey, but to anyone living at the time the trend would of higher generality. It is possible to observe only one member of one have been difficult to discern. Bacon hoped to replace the Aristotelian speciesof a universal of high generality and still correctly intuit that uni- deductive method with his method of i-rue induction, or induction by exclu- versal. usually more extensive observationsare necessary.The number and sion. Just as Aristotle had devised a set of lules for deduction, Bacon was variety of observations needed for intuition vary from person to person going to do the same for inductive logic. I{e hoped to produce an inductive and from subject mattel' to subject matter. Fewer observations are usually machine for grinding out true, scientific laws. necessaryin mathematics than in such empirical sciencesas biology. Nor Bacon's plan was to begin with extensive gathering of data without any did Aristotle think that the preceding enumeration of individuals could speculation.GIfe felt that the best way to preclude any premature specula- be complete, since he believed that there were indefinitely rnany individuals tion was to have this labor performed by unlettered underlings. Besides, in any species.It is not possible to observe all human beings and then he believed that it was "somewhat beneath the dignity of an undertaking merely by mechanically summing. their properties to discover their.essence- like mine that I should spend my orvn time in a matter which is open Intuition was necessary. to almost every man's industry."? No doubt comments like these prompted Little has been said thus far about intuition. There is very little to say. Harvey to say that Bacon wrote philosophy "like a Lord Chancellor." Bacon Although intuition is the source of all certain knowledge, Aristotle hardly was never to have his army of workers. Instead, in the last year of his mentions it. According to Aristotle, the essenceof mankind is to nous, life he himself tried to mal

degree. For example, if the nature of heat is under investigation, those and are deductive in nature. Aristotle was cognisant of this fact.8 Many things that seemed hot would be listed on the fir.st table, those that lacked later philosophers were not. This conflict between the desire to mahe induc- heat on the second, and variations in heat on the third. Only after these tion certain while still remaining inductive is evident in Bacon's writings. tables were filled out did induction actually begin. True induction for Bacon Induction by exclusion was not only a method of discovery but it afforded was induction by exclusion or, as it is sometimes called, complete elimina- absolutely certain knowledge. "Now what the sciences stand in need of tion. If the relevant concepts have already been formulated and if natural is a form of induction which shall analyse experience and take it to pieces, phenomena can be divided into a finite number of discrete natural kinds, and by a due process of exclusion and rejection lead to an inevitable then induction by complete elimination is possible. All the possible causes conclusion."0 of a kind of event can be listed and all but one eliminateci. But under Bacon nraintaincd that scientistswere to proceed from senscperception such circumstances induction by complete enumeration is also possible. of the individual to the lowest universals and from there gradually, without Bacon thought that the only induction recognized by Aristotle and prac- omitting a step, to axioms of greatest generality.'n Taken literally, this ticed by his followers was induction by simple enumeration as exemplified view of induction would completely eliminate deduction as anything but in argument (3). But Aristotle did not consider rhe process by which the an after-the-fact exercise,but on occasion, Bacon seems to think otherwise. universalswere abstracted from the individual as induction;it was intuition. Both deduction and induction have roles to play in science-"from the Induction of any kind could occur only at the level of universals, and new light of axioms, which have been" educed from those particulars by at this level both induction by complete enumeration and induction by a certain method and rule, shall in their turn point out the way again complete exclusion (or elimination) are possible, since Aristotle believed to new particulars, greater thir-rgsmay be looked for. For our road does in the existence of a finite number of discrete natural kinds. Argument not lie on a level, but ascends and descendsl first ascending to axioms, (5) below is an example of an induction by complete exclusion. then descendingto works."11 It is difficult to reconcile these remarks concerning the role'of deduction (5) Scalene triangles have three (6) Man, the horse, and the mule in science with Bacon's earlier pronouncements about gradual ascent. If sides. are longJived. the formation of concepts or the discovery of laws is to proceed by true induction, jumps, Isosceles triangles have three Man, the horse, and the mule step by step, without any how can a concept or a law be oI wider sides. are all bilelessanimals. scope than the evidence from which it was derived? To the extent that true induction is possible, the collateral security of deducing Equilateral triangles have three Hence, all bileless animals are new confirming instancesis impossible. sides. long-lived. Herschel, Mill, and Whewell all concurred at least verbally in Bacon's Hence, all triangles have three sides. confused distinction between deduction and induction in terms of increasing and decreasinggenerality, and much of lferschel and Mill consistsmerely in tidying up Bacon's methods of induction. Both authors, however, empha- The conclusion to argument (5) seemsto follow from the premisesneces- sized the role of deduction a good deal more strongly than Bacon had. sarily because of the suppressedpremise that these are all the speciesof For example, I{erschel says: triangle that there are. All speciesof triangle have been enumerated. when the suppressedpremise is added, the argument becomes deductive. Argu- It is to our immortal countryman Bacon that we owe the broad an- ment (6) is actually taken from Aristotle. Here, too, the cleductive nature nouncement of this grand and fertile principle; and the development of the idea, that the whole of natural philosophy consists entirely of of the inference is readily apparent. only if the three speciesmentioned are ail the bilelessanimals which exist is the argument valid. Both induction B. Aristotle,Posterior Analytics" 68b15, by complete enumeration and induction by complete elimination are possible 9. Bacon(1620), p. 19. 10. Ibid.,bk. 1, AphorismCIV. only in a world which is divisible into a finite number of natural kinds 11. Bacon(1620), bk. 1, AphorismCIII. 24 Darwin and Ilis Critics .rre Inductive Method 25

a series of inductive seneralizations, commencine \a,it[ the nrost circum- Herschel and MilI thought that both the logic of discovery and the logic stantially stated particulars, and carried to u.iver.sal la*,s, or axioms, of justification could be analyzed in terms of deduction and induction, which comprehend i' their statements every subordi'ate degree of gen- ryhereasWhewell thought that no simple rules could be given for the process erality, and of a corresponding seriesof inverted reasoning fÄm genäars to particulars, by which these axioms ar"etr.aced back into their ri*roresr of discovery.15For Ilerschel and Mill the key tool in the logic of discovery consequences,and all ltarticular propositiorrs deduced from them and justification was induction by elimination. 3ut it is very itnportant . to observe,that the successfulprocess of scien_ Darwin repeatedly made use of induction by elimination. For example, tific enquiry demands continually the alternate use of both the inductiue in his paper on the Parallel Roads of Glen Roy (1839), he reasoned that and de dt tct iue mcthod.r, these roads or shelves were caused by either lakes or arms of the sea. Herschel resolves tl-re conflicting roles of deduction and inductio' by If they were caused by lakes, then huge barriers had to be erected and observing that "in the study of nature, we must not, therefore, be scrupulous removed successivelyat the rnouth of the glen. Since Darwin could not as to hoza we reach to a l

12.Herschel (1830), pp. 104,174-t75 15. Ibid.,pp. 199,284; Flerschel (1841), pp. 196-197. 13. Ibid., p. 164. 16.September 6, 1861,More Letters (1903), 2:188. 14.Mill (1874),pp. 68-69. 17.Darwin (1958),p. 84. 26 Darwin and His Critics i'he Inductive Method 27

was not that the principle of exclusion could neuer be trusted but that be of greatest use to Darwin's critics was their contention that only logically it could never be trusted completely. It could, however, confer some prob- necessarymodes of inf erence aflorded proot'. Although MiU recognized the ability on a hypothesis. It could not in actual practice make a hypothesis importance of approximations in science, they were merely stages on the absolutely certain, since in the natural sciencesit is never possibleto elimi_ road to something better.zl Until this final stage was reached, proof had nate all alternatives. not been provided. The only reason for resorting to approximations was In his Glen Roy paper Darwin had obviously overlooked the possibility that the correct definitions had not yet been discovered, the phenomena. of ice barriers, but there were other possibilities as weil. For example, had not been correctly reduced to natural kinds. When they had been even if the shelves had been lormed by sea action, a gradual d"c."or. discerned, universal correlation was guaranteed.22In abstract scienceslihe in sea level would have explained ihem as welr as a gradual elevation zoology, botany and geology "a probability is of no account; it is but of the land. (In point of fact, the sea level had decreased 400 feet in a momentary halt on the road to certainty, zrnd a hint for fresh the preceding 1000 years.) In his coral reefs paper (1842) Darwin ex_ experiments,"23 plained the growth of coral reefs by reference to the gradual sinking of Mill has received considerable credit for not dismissing evolutionary the ocean floor. The facts, he contended, were inexplicable by any other theory out of hand as l{erschel and Whewell had done,2abut the credit theory. In this instance Darwin's theory was basically correct, but he had is not deserved.'z5Mill discussesevolutionary theory in a footnote to his not eliminated all the possibilities-to name one, a gradual increase in System of Logic, but only after treating Broussais' hypothesis about the sea level. (As mentioned previously, the opposite had actually occurred. localization of disease, Gilbert's contention that the earth is a magnet, Darwin also mentions certain phenomena which wourd have had the same and the suggestion that the brain be looked upon as akin to a voltaic effect as a drop in sealevel.) pile. Finally, Mill says: Darwin also used this line of reasoning in the Origin of Species (p. 33) and, The Descent of Man (p. 269). Again he had not eliminated all pos- fuIr. Darwin's remarkable speculation on the Origin ot' Speciesis an- other unimpeachable example of a legitimate hypothesis. What he terms sible alternatives, bur he did think that he was justifiecl in cliscounting the "natural selection" is not only a uera causa, but one proved to be capable current explanation in terms of special creation. I-Ie dismissed it, not of producing effects of the same kind with those which the hypothesis because it was an i'correct scientific explanation, but because it was not ascribes to it: the question of possibility is entirely one of degree. It a proper scientific explanation at all. "I would give absolutely nothing is unreasonable to accuse Mr. Darwin (as has been done) of violating for the. theory of Natural selection, if it requires miraculous additions at the rules of Induction. The rules of Induction are concelned with the conditions of Proof. Mr. Darwin has never pretended that his doctrine any one stage of descent."18Darwin's reasoning on this issue will be ex_ was proved. I-Ie was not bound by the ruies of Induction, but by those amined later in chapter 4.1e It might also be mentioned that Bacon was of Hypothesis. And these last have seldom been more completely fulfilled. no more successful than Darwin in eliminating all alternative explanations Ile has opened a path of inquiry full of promise, the results of which for phenomena he was investigating. For example, his explanation of the none can foresee.And is it not a wonderful feat of scientific knowledse tides was erroneous because, in opposition to Garileo, he discounted the and ingenuity to have rendered so bold a suggestion, which the fiÄt impulse of every one was to reject once, admissible and discussabie, rotation of the earth. Galileo's explanation, however, was equally at erroneous.2o evelras a conjecture?'?6 The method of exclusion, when incomplete, failed to provide absolute Mill's endorsement was a double-edged l

philosophers set, it might not be the theory that was at fault. what then from a law, that law must be universal in form. Neither. deducibility nor is the current view on the philosophy of science? How does evolutionary the universality of the relevant laws can be abandoned without losing this theory, both in its original form and in its modern reformulations. measure eleganceand simplicity. Flowever, many putative laws in science,especially up to today's standards? in biology and specifically in evolutionary theory, are not universal in form. The most widely accepted moclel of scientific method.among logical em_ Thev are statistical.statements, trend and tendency statements,and approxi- piricists is termed the hypothetico-cleductivemodel (H-D model). On this rlations. From the statement that blue-eyed couples almost always produce' model, a hypothesis is formulated in some unspecified manner and then blue-eyed children, it is impossible to deduce the eye-color of a particular checked by deducing va'ious consequencesfrom it. If the deductions turrr child. I{orvever, it can be inferred tl-rat it is highly likely that all of the out to be true, then the hypothesis is gradually confirmed. No scientific clrildren of a blue-eyed couple, ceteris paribus, will have blue eyes. The hypothesis, however, is ever completely confirmed or verified. Scie.tific inferenceis inductive. laws are universal in form, and not all consequencescan be crrecked.How- If all less-than-universalstatements are interpreted merely as particular ever, if one of the deductive consequencesof the hypothesis turns out to statements which assert o,nly that at least one subject has the predicate be false, the hypothesis is immediately shown to be false and must be indicated, then the relation between verification and falsification is reversed. rejected.I{ence, falsification is very easy. \/erification becomes easy; falsification impossible. But scientists do not The I{-D model has the virtue that it does not prescribe any rigid proce- treat all less-than-universal statements as particul:rr statements. There is dures in discovery. There is no cut-and-d'ied rogic of discovery. certainly considerabledifference between the claim that 99 percent of smokers wili there may be methods of scientific investigation which have proved fruitful die of lung cancer and the claim that 1 percent of them wi1l. This difference in the past and are more likely to produce results than others. For example, is the subject matter of statistics and probability theory. In this type of analogiesand models are two very effective means of discovery,while simple inference, neither verification nor falsification is easy. In neither case will trial-and-error is not very efficient. But the chief virtue of the H-D model a single observation suffice-even in principle. Populations have to be de- is that it recognizesthe impossibility of absorute proof for any scientific fined and samples taken. Currently, philosophers of science are trying to theory. According to the method of "inverse creduction" incorporated in iormulate ivhat might be cailed a hypothetico-inductive model of science, the H-D model, a scientific theory can become increasingly more probable; but it is proving to be a very frustrating task. Numcrous troublesome para- that is all. rn inverse deduction, one reasons from the truth of specific doxeshave arisen,and few solutionshave been forthcoming. inferences made from a law to the increased likerihood that the law is How appropriate are current schematizations for evolutionary theory? true. From the point of view of deductive logic such inferences arc fal- Darwin maintained that the Origin was one long argument and a convinc- lacious-the fallacy of affirming the consequent. of course, early philoso- ing one at that: phers of science recognized the method of inverse deduction but thousht Sorne of my critics have said, "Oh, he is a good observer, but has it was oniy a temporar.yheuristic device. no llower of reasoning." I do not think that this can be true, for the As might be expected from its brevity, the foregoing clescription of the Origin of Species is one long argument from the beginning to the end, I{-D model is overly sirnple. IJypotheses are not tested in isolation but and it has convinced not a fe'rv able men. No one could have written embedded in theories. Thus, if a decluctive consequenceof the theory turns it without somepower of leasoning.3t out to be false, a single hypothesis is not falsified. I{ather, any one of An argument it may be, but the traditional notions of deduction and severai hypothesesand observations may be at fault. rnstead of abandoni'g induction were completely inadequate for characterizing it. For example, a theory upon a negative deduction, the theory is usually modified, and Darwin saysin the opening paragraphs of the Origin: considerable latitude is permitted in the degree of modification permissible ,,same,, while still terming the theory the theory. For I am well aware that scarcely a single point is discussedin this volume on which facts cannot be aclduced, often apirarently leading to The eleganceand simplicity of the H-D model stems from its deductive character. In order for singular observation statements to be deducible 31. Darwin (1958),p. 140. rz20 : Dar.winand His Critics i The Inductive Method JJ conclusions opposite to those at which I have arrived. A fair resurt can sequencesof the law. Darwin's basic principles related inferentially be obtained only by fully.stating were u"a Uofun.ing th" fr.i, il;;;;""., i on both sidesof each question; but not in a strict deductive hierarchy. Evolutionary theory was basically and this cannot possiblybe here däne-r, i' statisticalin nature. The relevant inferenceswere inductive. In a letter to Il. G. Bronn, Darwin ,.you Charles S. Peirce was one of the few philosophers admits, put very well and very who recognized and fairly that I can in no onc i.stance exprairr the course of modification emphasized the statistical nature of evolutionary theory. FIe saw Darwin's in any particular instance."ss If theory as one more application of the statistical method which evolution by natural selection was to be Maxwell accepted at all, it woulcr (1831-1879) have to be "chiefly from trris view connecting had used so successfullyin physicsand Quetelet (1796-1874) under an intelligible point of view in sociology.s?The work of these men and had prepared the a host of facts. when we descend to others scientific details, \,\'ecan prove that no community one specieshas changecl; nor can we prove for "the idea that fortuitous events may result in a physical that the supposed changes are beneficial, law."38 Peirce's accurate understanding which is the groundwork of the of the structure of evolutionary theory. Nor can we explain why some species have changed and others theory is sufficiently rare to warrant reproducing in its entirety: have not."3r As Huxley The Darwinian cont,lol,ersyis, in large part, a question of logic. Mr. observed, the origin is "a mass of facts crushed and pounded Darwin proposed to apply the statistical method to biology. The same into shape,rather than rreld together by the orclinary mediurn of an obviorrs thing has'been done in a widely dif{erent branch of science, the theory logical bond; due attention will, *,ithout doubt, clisco'er this bond, but of gases.Though unable to say r,irhat the ,movements of any particular it is often hard to find."35 The modern reader frequently grows impatient molecule of gas would be on a certain hypothesis regarding the constitu- with Darwin's method in the tion of this class of bodies, Clausius and Maxwell were yet able, by Origin of piling example on example, but this was the the application of the doctrine of probabilities, to predict that in the only rnethocl open to hirn given ti-restructure of evorutionary long run such and such a proportion of the n-'roleculeswould, under theory' This format is still characteristic of works in evorutionary theory.36 given circumstances, acquire such and such velocities; that there would As Darwin formulated it, evolutionary trreory clid not permit verification take itlace, every second, such and such a number of collisions, etc.; or falsification by the simple expedient of deducing a single observational and from these propositions they were able to deduce certain properties consequenceand checking of gases, especially in regard to their heat-relations. In like manner, it. Given Newton's equations and a few reason- ably unproblematic simplifying Darwin while unable to say what the operation of variation and natural assumptions and boundary conditions, a physicist selection in every individual case will be, demonstrates that in the Iong could deduce some fairly precise observational consequenceswhich run they will adapt animals to their circumstances.Whether or not exist- could be used to confirm or disconfirm his theory. He courd deduce where ing anirnal forms are due to such action, or what position the theory Mars should be at a precise time. Darwin's theory was neither mathematicar ought to take, forms the subject of a discussion in which questions of in notation nor deductive in form. Given evolutionary theory and the kind fact and questionsof logic are curiously interlaced.3e of data available to a biologist, no precise,unequivocar inferencesrvere possi- Although Peirce was almost alone in approving of ble' one the form of Darwin's could not predict how an extant spe;ies wourd evorve or retrodict theory, he joined the majority in rejecting selected parts of the content. how an extinct species did evolve. At best, only a range of some more He preferred Agassiz'sEssay on Classification (1859).40 In 1893 he passed or less possible outcomes could be generated. In this respect) Darwin,s the following judgment on evolutionary theory: theory was at a decidecl disaclvantage.The two means of verification recog- nized in Darwin's day were What I mean is that his hypothesis, while without dispute one of the deductive subsumption of one general law under a more general law the most ingenious and pretty ever devised, and while argued with a and the deduction of specific observationar con- 37. JamesClerk Maxwell was a Scottishphysicist whose famous equations revolu- 31. Darwin (1S59),p. 2. tionizedphysics. M. A. Quetelettrsed statistics in a rudimentaryway in compiling 33. 5, t860,i4ore figures{or crimesand suicides;see O_uetelet(1846). Herschelreviewed this work _October Letters(1903), I :172_17J.- - ' 34. Dawin, Lile an'dLetters (1887),ZriiOt. " in the EdinburghReaieu (1850), 42 i1-57. 35. Huxley(t896), p. 25. 38. Peirce(1935), 6:297. 36. (1877\. SeeDobzhansty (tStZ;, Mayr (1942and 1963). 39. Peirce 40. Peirce(1931), 1;203-205. 34 Darwin and I-Iis Critics fhe Inductive Method 35

t, wealth of knowledge, a strength of logic, a charm too crude to permit an adequate formulation of evolutionary theory. In- of rhetoric, and above i: all with a certain magnetic genuinenessthat was almost irresistible, did stead, they cail for a molecular version of evolutionary theory, hoping in not appear, at first, at all near to being proved; and to a sober mind this manner to fulfill the requirements of the H-D model.as This reductive its case looks less hopeful now than it did twenty years ago.41 maneuver is quite common in science.Whenever laws at one level of analysis appear indeterministic, analysis of the phenomena at a lower level often At the turn of the centuly, the fortunes of evolutionary theory had relations are closer to universality. The only thing that stands' reached their lowest ebb. Physicists to a man had proved that the earth reveals which in the way of true, universal laws is accuracy of measurement and the was not neariy as old as Darwin's theory required. Geneticists such as level analysis. It should be remembered, however, that after years of de Vries and Morgan were claiming that mutations were discrete, not of successin physics, the reductive program was frustrated at the subatotnic gradual; thus, Darwin had been wrong in thinking that evolution was gradual. The excessesof evolutionists like Haeckel and the disputes concern- level. alternative, philosophers of science have more work to do' ing orthogenesis and neo-Lamarckianism had earned for evolution a de- On the first cideclly bad reputation. It was more metaphysics than science.a2One would They have to work out the details and general outline of a reconstruction expect the situation to irnplove consiclerablywhen physicists and geneticists of science appropriate to evolutionary theory in its present form. After much better evolutionary theory looked when Peirce switched discoveredtheir errors, and it did, but the problem of the form of evolution- all, notice how to the Maxwellian paradigm. On the second alternative, ary theory remained unchanged. It was still, at best, pr.obabilistic. In the from the Newtonian have more work to do. They have to produce a scientific theory 1930's Fisher, Haldane, and Wright attempted to use the recent advances biologists universal laws which permit specific predictions. On either in genetics to produce a theory of evolution which was both mathematical consisting of theory and philosophy of science are still at odds' and genetical. The unit of evolution became the gene, and evolutionary view, evolutionary Most of this chapter has concetned the detrimentil effects of early phi- change was to be measured in terms of changes in gene frequencies.Even of scienceon the reception and accePtanceoI evolutionary theory' so, the situation with respect to verification did not irnprove much. Given losophies must be said in defense of these systems.When early philoso- modern evolutionary theory, knowledge of mutation rates, rates of difier- A few words were not concerned with rigid proof and certainty, much ential reproduction, and so forth, the best that a modern evolutionist could phers of science to science in general and to evolutionary do was to provide a distribution function of possible outcomes.a3 that they said was applicable (Compare Hopkins' strict interpretation with Fawcett's Two alternatives seem open to us at this juncture: either revert to a theory in particular. treatment in this volume.) For example, Bacon provides hypothetico-inductive model of science or argue that evolutionary theory more informal devices to help in scientific investigation. These praeroga- after a century is still inadequately formulated and that in a more finished a list of auxiliary instantiarunl are much more original and applicable to actual scientific form will conform to the lI-D model. The problem with the first alternative tiue than his methods of true induction' Almost everything that is that there is no H-I model. Thus, this alternative reduces to the admission investigation had to say about the discovery and verification of scientific the- that there is no reconstruction of scienceappropriate to evolutionary theory I-Ierschel not being rigorous-fits evolutionary theory perfectly. as it now stands. Biologists are currently working on the second alternative. ories-when he was is similarly reievant when he is discussing such things as multiple Some are attempting to reformulate macro-evolutionary theory more rig- Miil approximate generalizations,and probable inference. orously so that deductive confirmation or disconfirmation is possible.aa causation, Even the extensivefact-gathering encouraged by these empiricist philoso- others find evolutionary theory in terms of organisms and their interactions phies of science was not entirely detrimental to evolutionary theory, given 41. Peirce(1935), 6:297. its statistical nature. Darwin did not waste the twenty years preceding 42. unfortunately,space prohibits us from pursuingthe history - of the reception tlre publication of the Origin. Only such a wide sarnpling of data had of evolutionarytheory during this period. Peter Vorzimmer (lg70) has wiitten an informedbut uneventreatise on these"years of controversy."see also provine the slightest chance of supporting it. The relation between Whewell's phi- fl971). 43. See,Ior- exalnple,Lewontin (196g); for fur-thercliscussion sec Hull (1974), 44. MacArthurand Wilson (i967) andWilliams (I9?0). 45. Schaffner(1969). $. 36 Darwin and His Critics K. & losophy of scienceand evolutionary theory is even more equivocal. Nothrng H" in Whewell's second-levelphilosophy of science was incompatible with evo- f lutionary theory. He did not concur in the popular conviction that a strict M, logic of discovery would assure truth. In the colligation of ideas why not superinduce the idea of evolution by natural selection on the facts? Certain $. ideas are self-evident. Why not evolution? The answer can be found at ki a deeper level in a belief which Whewell shared with Aristotle, Bacon, N Herschel, ' and Mill, a belief in the existence of natural kinds definable $. 3 Occult Qualities by a single set of necessaryand sufficient conditions, a belief in essences. $], Empiricists wanted to eliminate so-called "occult qualities" from science and yet they retained that element in earlier philosophies which contributed $', Nineteenth-century scientists were in agreement that all references to the most to the prevalence of metaphysical entities-essentialism. $' $. occult qualities should be excluded from science, but they were not clear as to rvhat it was about a quality that made it occult. Bacon thought that such Aristotelian notions as the hdt and the moist were occult qualitres ili"r but that his own explanation in terms of the movement of unobservable particles was perfectly acceptable. Newton thought of light as being cor- puscular but excluded all reference to such theoretical entities from his published writings. Such hypothesesas light corpuscle! and the aether had no place in science.Darwin found Forbes's explanation of the distribution of living creatures in terms of polar principles absolute rubbish, on a par with magnetism moving tables. Owen's Law of Irrelative Repetition in terms of a polarizing force opposing the Platonic rati'o was scarcely better. Yet his own theories necessitated unobservable gemmules and the spon- täneous generation of the original life fonns in the distant past. Mendel claimed that he defined constancy of type merely as the retention of a character during the period of observation, yet could not avoid postulating unobservable"factors" as the cause of his observed ratios. In the preceding chapter, the Victorian aversion to speculation in the senseof large inductive leaps was examined. In this chapter we will deal with speculation in the senseof unobservable entities, substances,and properties. The crucial dis- tinction is between theoretical entities for which indirect evidence can be obtained and metaphysical entities which are unobservable in principle.

Bacon intended the notion of gradual induction and complete elimination to insure Ihe truth of the generalizations derived, but induction from ex- perience also served a second function in empiricist epistemology-to insure the empirical content of scientific terms. If scientific concepts are abstracted from experience, regardless of how large the inductive leap, they will still be grouncled in experience and not empty verbiage. From Bacon and New- 3B Darwin and His Critics Occult Qualities 39 ton to l{erschel and Mill, scientistsand empiricist philosophers had a deep- rras known by intuition, and intuition was infallible. Observation might seated aversion to what they viewed as Scholastic occult qualities. One rvell excite intuition to act, but only intuition was capable of apprehending of the primary goals of scientistsduring and after the scientific revolution the tme objects of scientific knowledge-eternal, immutable essences.The was to make certain that scientific concepts and generalizations were not most obvious objection to Aristotle's postulation of infallible intuition is empir'ically meaningless. The issue was not whether a scientific generaliza- that people do make mistakes. In fact, almost everything which Aristotle tion was true but the more basic question of whether or not it was empiri- himself claimed to have intuited turned out to be false. Several evasive cally rneaningful. nraneuversare possible for saving the notion of infallible intuition. The Aristotelian science, in the.hands of the Scholastics, had degenerated extent to which one uses one of these maneuvers determines exactly how to such an extent that many putatively empiricai claims were actually im- rnetaphysicalthe notion of intuition itself becomes. mune to experimental disproof. Such notions as the hot and the moist One way to salvage the notion of infallible intuition is to deny the status had begun in Aristotle as observational terms. If something felt hot, then of intuition to any process that eventuates in falschood. "You say that it was i'rot. But gradually these rerms took on additional dimensions.Maybe vou intuited that all crows are blaclphysiology, or meteorologY,were explained in the last analysis in their opinion tl-rat scientific laws l-rad to be universal in form. One way by reference to these four qualities. The four basic elements of physics to save the universality of scientific laws is to discount all exceptions as were fire, air, earth, and water' Whatever properties fire had were due monsters,as not propeily fitting the definition of the names of the classes to its being hot and dry, air hot and moist, and so on. The four humors of entities related in the law. Once the phenomena have been properly forrred the foundation of Aristotelian physiology. Yellow bile (or choler), reduced to natural kinds, universal laws must be forthcoming.a like fire, was hot and dry, black bile (or meianocholer),like air, was hot In their investigations, scientists tend to concentrate on exceptions to and moist, and so on. In a healthy person these four humors were balanced, their laws with the hope that such an emphasis will Iead to their improve- but when one of them gained ascendancy,iilness resulted. Therapy consisted ment. Like essentialists,they hope to discover true, universal generalizations; in attempts to reinstate this balance' but, unlike essentialists,they tend to change the law to accommodate the This system cannot be eiaborated any more fully here' The purpose exception rather than to dismiss the exception as inexplicable. The end of introducing it at all is to show that as a systemof interconnected concepts result of tl-re essentialist distinction between essentiai and accidental at- it is not different in kind from modern scientific theories' Changes in one element in the systemhave ramifications throughout the system' For example' 2. This view in biology can be traced back at least to William Harvey, who physics of natural place, the natural place for earth was at in 1657 observed that the laws of nature can often be discerned by careful investiga- in Aristotle's tions of rareties. the center. Copernicus, by placing the sun (fire) at the center, considerably 3. Darwin (1958), p. 123. astronomical computation, but he overturned all of Aristotelian 4. Mill (1874), p.3BB. simplified &il +2 Darwin and His Critics It. Occult Qualities +3

physics, and indirectly physiology, meclicine, meteorology, and so on. Aris, fi tributed to predominance of phlegm by one physician and of biie by another, totelians had good reason for rejecting Copernicus, suggestion. $r and there would be no experiential way of resolving the dispute. Extreme Because bile was part of this loosely lr connected system of concepts, its reliance on authority became more and more the order of the day. presence or absence was not purely Nr: a matter of observation. some animal F' Bacon and Newton attributed the degraded state of Scholasticphilosophy might possessbile, though none was discernible, and others rack it, though $ti both to a penchant for rash, inductive leaps and to a weaknessfor occult a bitter fluid could be extracted from the river. similarry, some animal $nl qualities. In order to avoid reference to occult quaiities, they proposed might feel no colde' or moister than t. another animar, but because it was that science should make leference only to those entities, substances,or iower on the scale of being, it .,Cold,, $, hacl to be colder and moister. and gualitieswhose character or effects could be immediately shown. For Bacorr, "moist2' became theoretical terms connected only indirectly to our feelings It this proposal took the shape of fulminations against forms. Newton ex- of cold and moisture. Because of the subsequent history of Aristotelian tL. lrressedthe same messagein his cryptic hypothesisnon fingo.u The manifesto science and its distance frorn us in time, modern readers might be tempted was easier to proclaim than to'practice. Bacon realized that his tables to dismiss the whole system as metaphysicar nonsense,but Aristotre,s proce- ': could be used to abstract forms as easily as causes,and he went to great dure of inventing theoreticar entities which cannot be observed directly .. lengtl-rsto assule his readers that this was not what he was doing. Although is not significantly different from modern scientific method. lre refelred to "forms," he did not mean anythins like Aristotelian essences: Today we explain the recurrent fever and chills of malaria by reference to the life plasmodium cycle of a species of rather than bv the cvclical I cannot too often warn and admonish men against applying what overpredominance r' I say to those forms to which their thoughts and contemplations have of blood and phregm. we berieve the action of ,t * hitherto been accustomed . For when I speak oI forms, I mean noth- protozoan on the blood cells can be explained in terms of the morecurar ing more than those laws and determinations of absolute actuality which structure of DNA and RNA, and this structure in terms of molecules, govern and constitute any simple nature, as heat, light, weight, in every atoms, and various subatomic particres. Aristotre stopped at the lever of kind of matter and subject that is susceptibleof them.6 the four qualities. Today we stop at the level of quantum mechanics. There is no doubt The distinction toward which Bacon was groping was between concepts that our explanation is far superior to that of the ancient and laws, between defining a concept in terms of a set of covarying charac- Greeks. Care must be take', however, in identifying the features of the mode'r explanation ters and combining concepts thus defined into empirical laws. In actual whicrr make it preferable to earlier explanations. It does not lie, practice, Bacon's efforts at discovering causes by his inductive method as scientists in Darwin,s day contended, in the paucity of differed little from those of the overlook the "grand distinc- unobseruableentities. Scholastics.To The elernents ,,occult,,, tion" between the coexistence of characters and the successionof phe- in Aristotelian natural scietrce became not be_ in cause of the nomena time was, as it seemed to Mill, "the capital error in Bacon's happenstance that the human organism cannot sense them directly (after view of inductive philosophy."? The conceptuai shift which made the recog- all we cannot perceive ultraviolet right) but because the nition of this distinction more obvious from an ontology system in which was the change the concepts were embecrcredwas sc loosely organized of substancesand attributes to an ontoiogy of events. The paradigm of that little in the way of indirect evidence was possibreeither. For exampre, causationhad become one billiard bail hitting another. ever.rthough we cannot see ultraviolet light, this light has certain effects In Bacon's work, as well as the Scholastics',the search for laws of nature on our skin which we can detect..Numerous predictions can be made about what ultraviolet too often resulted in the enunciation of definitions,sbut of equal importance light should do, given current theory. The four qualities and other elements in Aristotelian ph1,5is5started out as observablesand 5. See discussionin the review by Wright included in this volume. progressed gradually to the rever of unobservabres,but this deveropment 6. Bacon (1620), bk.2, Aphorism XVII. i. Mill (1874), p.381. was not accompanied by a con"esponding increase in precision in the sys_ B. The confusion of definitions and laws is still quite common. For example, temic interrelations of the more theoretic concepts and between them and D. R. Cressey,using von Hartmann's method of analytic induction, ends up defining "iriminal violation of financial trust" instead of discovering its causes.See Cressey possible observations. For example, a newry discovered diseasecourd be at- (1950) and Robinson (1951). 44 Darwin and I-Iis Critics Occult Qualities 45

was the nature of the attributes referred to in these definitions. Although universally admitted theory of the undulation of light,-neither the un- Bacon tried to restrict himself to observablefacts and nothing but observable dulation, nor the very existence of ether being ploved-yet admitted becausethe views explain so rTluch.l! facts, he was no more able to do so than scientists of other ages. In fact, many of Bacon's most significant errors stemrned from his over-reliance \:. Finally, he wrote to Lyell: on superficial appearances. Like Aristotle, he argued tl-rat the earth did f With to Bronn's objection that it cannot be sl'rown how life '' not seem to move; hence, it did not move. Like Aristotle, he believed {, respect f- arises,and likewise to a certain extent Asa Gt'ay's remark that natural in the spontaneous generation of macroscopic organisms because careful !- i:. selectionis not a aero:caLrsa,I'"vas much interestedby findi1g accidentally observation showed it to occur' "in animalculae generated from putrification i, in Brewster'sLife,of Newton, that Leibnitz objected to the law of gravity as in ants' is. As it has chanced, eggs, worms, flies, frogs alter rain, etc." Bacon did concede i becauseNewton couid not show what gravity itself that more carefui observation was still called for.e In Darwin's day, Sedg- i I have used in letters this very same argument, little knowing that any larv of gravity. Newton answers by wick argued that we should accept the fossil record as we find it, one had really thus objected to the saying that it is philosophy to make out the movements of the cloch, not interpolate unl

I-Ie declares very freely that rre lays down this attraction, onlv as a rntities and qualities and to attribute to them the characteristicsthe theory cause which he knows not, and whose effects he only considers,.oäpu.", required. and calculates; and in order to avoid the reproach of reviving'the öccult postulate anything which Justified or not, Newton did not like to have to qualities of the schoolrren, he says, that ie establishesnoie but such even slightly resembled an occult quality. On this score, Darwin was at Qualities as are rnanifest and very visible by their phenomena, but that had to postulate no new or sub- the causes of these Quarities are indeed occult, a;d that h.' leaves it a considerable advantage. Darwin lorces to the other Philosophersto searchinto them.rs slances.FIe merely showed the possible,almost the inevitable, consequences" of fairly common observations about the organic world. Offspring vary But the Scl-roolmenalso claimed that their qualities were manifest. After sliglitly from each other and from their parents' More offspring are pro- all, what is more ma'ifest than the hot and the cold, the dry and the reasonable to expect differential mortality .,hotr,' .,moist," duced than can survive. It is moist? In fact, of course, the technical terms and so on, as a lunction of these variations. And so on. Darwin introduced nothing I'rad lost their original experiential connotations, but so had the notion that fainrly approached an occult quality, metapirysicalentity, or vital force. of force in Newtonian theory. It rrad little to do with the feerins one Although an occasional author with extreme effort was able to read his gets when lifting a heavy object. relerencesto natural selection as a reificatiou of Nature selecting,Darwin's The feature of Newton's gravitational theory which i-ris contemporaries tlieory was purely naturalistic.20 found most objectionable was its apparent reliance on action at a clistance. when Dar.win,s critics objected to his evolutionary theory as hypotheticai Gravity acted instantaneously in the abser-rceof contact throughout all and speculative, they had in mind three features of his formulation: (1) space.one way to eliminate such a counter-intuitive notion was to postulate evolution occurring so slowly that no one had observed or was likely to a universal ether per-vading all space. prior to Newton, scientistshacl fre- observeone speciesevolving into another; (2) the initial spontaneousorigin quently postulated subtle fluids to explain natural phenomena, especially of life being in the distanr past and unknowable; and (3) Darwin's uncau- in biology, but such fluids were lookecl upon with some clegreeof suspicion. tious assertion that aII specieshad evolved and most likely from a single with the tremendous successof Newton's theory, the postulation of subtle ionn. fluids as explanatory principles became respectabre. For instance, in his Darwin grew weary of telling people that he did dot pretend to address review of the origin included in this volume, Flopkins justifies Lamarck,s clirect evidence of one species changing into another. Among those rvho vital fluids by comparing them with the luminiferous ether. Thus, Newton contributed most to Darwin's wearinesswas Huxley. Throughout their col- contributed unwittingly to two opposing trends in science-the rigid, overly laborarion, I{uxley steadfastly maintained that intersterilitv infallibly dis- restrictive, ultra-empirical inductive method and the almost unlicensed in- and "until selective breeding is definitely proved to give troduction of subtle Iluids.le tinguished species rise to varieties intersterile with one another, the logical foundation of There was a diflerence betwee' the occurt qualities of trre schoolmen the theory of natural selection is incomplete."2l Dalwin believed, on the and Newton's light corpuscles and gravity, and it was the difference which other hand, that it was clifficult "to make a marked line of separation Newton himself pointed out, but for different reasons. when attacked, betweenfertiie and infertile crosses."t' Moreover, those groups distinguis|ed Newton retreated to mathematics. He invented no hypotheses.He offer.ed those distinguished no by constant characters did not always coincide with mecha'isms. He simply supplied the equations which accounted for by sterility. As the years went by Darwin bccame resigned to the various phenomena rnathematically. (A similar retreat has occurred in this century disagreement: in quantum mechanics.) Newton need not have retreated. Because he could and did provide laws which accuratery accounted for a wide I did not understand what you required about sterility: assuredly the nange of phenomena with a greater degree of accuracy then any previous facts given do not go nearly so far. We dif{er so much that it is no in recently formed theory, there was good reason to believe in the existence of the postulated ,s" urltritg. To get ih" d.gt." of sterility you exPect Wollastonincluded in this volume' lB. Newton (1958),p.463. 20. See, for example,the review by 19. SeeThomas Llalt (1968). 21. Hrrxley(1896), P. vi. 22. Augusti, 1860,More Letters (1903)' 1:166' 50 Darwin and I{is Critics Occult Qualities

varieties seems to me simply hopeless. It seems to be almost like those , not untii recently has anything like the observation of the evolu- naturalists who declare they will never believe that one species turns of new speciesof muiticellular organisms been observed. (The develop- into another till they seeevery stage in the process.23 of speciesby polyploidy has been observed on occasi.on,but this is You a Darwinian method of evolution, and the evolution of new species _ will say Go to the Devil and hold vour tongue. No, I will nor hold my tongue; for I must add that after going, for my present book, :bacteria is commonpiace.) Yet, few reasonable merr withheld consent all through domestic animals, r have come to the conclusion trrat there itlu theory that species have evolved and that -natural selection is the are almost certainly several casesof two or three or more speciesblended icf {if uot the only) mechanism involved. together and now perfectly fertile together.2a or example, even in Darwin's own day, F. J. Pictet contended in his You are so terribly sharp-sighted ancl so confoundly honest! But to of the Origin of Species (1860) that he would not accept Darwin's tiie day of my death I will always maintain that you have been too dtductions until he saw for himself the evoiution of a new organ' By 1864 sharp-sighted on hybridism.,5 t had been converted and in 1866 published a paper in support of ionary Lheory (Pictet and Humbert, 1866). Needlessto say, the direct Two points are at issue in the preceding quotations: the scientific issue he required had not been supplied. Instead, he had been convinced of the sufllciency of sterility as a criterion for speciessratus and the philo- ttry the numerous indirect proofs of evolutionary theory. On this score special sophical question concerning the need for direct confirmation of theories. n and evolution by natural selection were on different footings. No we cannot treat the scientific question here, since the literature is volumi" i;i" ftra seena new speciesevolve anymore than they had seen.onespecially nous. All that can be mentioned is that one of the cornerstones of the but unlike the special creationists,Darwin had presented a mecha- synthetic theory of evolution is the biological definition of "species" in for evolution. Certain implications of his theory could be checked terms of interbreeding, potential interbreeding, and reproductive isolation.2. :rana lis theory as a whole gradually confirmed or disconfirmed without Darwin argued against intersterility as a criterion for species status and i,rbe direct observation of speciesevolving. Special creation was little more for the constancy of characters. Modern evolutionists argue against the c'- ,than a bald assertion. Whether as a natural event lacking any scientific terion of constancy of characters and for reproductive isoration (which eiplanation or as a supernatural event, special creation could be checked in several important respectsis different from intersterility).2, ,Qälyby direct obseiwation. As Darwin was to discover in his attempts to The question that interests us here, however, is whether or not Huxley against the "theory" of speciai creation, ib was even lesswell-organized was justified in requiring direct evidence of evolutio' by natural selection .q1gue ,thanAristotle's doctrine of polar principles and humors. before accepting the theory without reservation. Either Huxley is wrong i, ,Confirmation of a scientific theory by reasonably direct means is always in his views on the relation between direct evidence and proof or eise , welcome,but such confirmation comes long after the theory has been estab- the majority of scientists have been mistal

/.,dr_i'r\qgir*\ ,r'1,.; I 1;1;1;1it,1..\'1.5 \n i ui,EfdfJlllllilt t:

52 Darwin and FIis Critics Occult Qualities 53

to the initial spontaneous generation of living creatures from nonliving tion and extinction of the past and present inhabitants of the world should su!512n6s5-lut not very. have been due to secondary causes,like those deterrnining the birth and Before Dar-win, the common ploy in dealing with origin the of species death of the individual."sa In this opinion Darwin agreed with the leading by natural or supernatural means was to dismiss the question as dealing authorities of the day. With one or two exceptions, the author of every with events that occurred too long in the past ever be to known. I{ence, $r review in this collection concurred with this view of God_as acting through scientists wexe free to believe as they saw fit, and they generally saw fit exceptionlesslaws, not by rniraculous special creations. Even so, Darwin to believe in accordance with revealed religion. mystery of creation "The il was unhappy that he had gone so far and wrote to Hooker, "But I have is not within the legitimate territory of science." Theology must be assidu- $' long regretted that I truckled to public opinion, and used the Pentateuchal ously excluded from the dynamical sciencesbut was a necessaryadjunct N cappeared' N. term of creation, by which I really meant by some wholly un- to the historical sciences,es i known process."35 Darwin was presented with a dilemma. The currentiy popular doctrine Darwin was never to resolve this dilemma, but there is little doubt as of the miraculous creation of species,a flashing together elemental of atoms il to which alternative he preferred. As iate as 1870, he can be found saying: into fully formed plants and animals, ran counter to the naturalistic tenor of evolutionary theory and its author.3o He maintained that if he were Spontaneousgeneration seemsalmost as great a püzzle as preordination, I I cannot persuade myself that such a multiplicity o{ organisms can have forced to introduce "new powers" or "principle of improvement," he would li been produced, like crystals, in Bastian's solutions of the same kind. I reject his theory of I natural selection as "rubbish."sl Darwin felt himself i, am astonished that, as yet, I have met with no allusion to Wyman's committed to a naturalistic explanation of the initial origin of species. ! positive statement that if the solutions are boiled for five hours no or- Ile had none. To make ii ganisms appear; yet, if my memory servesme, the solution when opened matters worse, the naturalistic explanation for s to air immediately becomesstocked. Against all evidence, I cannot avoid the origin of life, the spontaneous generation of life, had a decidedly bad f, suspecting that organic particles (my gemmules from the separate cells reputation in scientific circles.s2The spontaneousgeneration of multicellular of the lower organisms!) will keep alive and afterwards multiply under organisms had been disproved after years just time il of laborious effort, in proper conditions. for its advocates to switch their allegiance to microbes. It was Darwin's i., What an interesting problem it is.36 misfortune to propose his theory of evolution, which seemed to necessitate i il It is frequently argued that evolutionary theory was wasted motion unless the spontaneous generation of the original forms of life, at the same tirne Darwin could also show how the first forms of life originated. In his defense, that Pasteul was beginning to route spontaneous generation from its last i t' Darwin once again sought refuge in the authority of Newton: refuge. "All life comes from pre-existing life" was the popular dictum. i: In the Origin Darwin bowed to protocol and referred to the first creation i, [Bronn] seems to think that till it can bö shown how iife arises it seemsto me about of lile by means of a supernatural metaphor. "There is a grandeur in I is no good showing how the forms of life arise. This as logical ' (comparing very great things with little) as to say it was this view of life, with its several powers, having been originally breathed l no use in Newton showing the laws of attraction of gravity and the into a few forms or into one."33 Later he added, "by the Creator.', Such I consequent movement of the planets, because he could not show what a reference to the diety, however, did not necessarily commit Darwin to the attraction of gravity is.37 a miraculous creation of life. "To my mind it accords better with what i In this instance Darwin's defense is apt. Newton, like Darwin, felt that we know of the laws impressed on matter by the Creator, that the produc- i he had accomplisheci something by his theory even though he had left somequestions unanswered; e.g.,questions concerning the nature of light and 29. Whewell ( 1840), 3:639; seealso Wollaston,sreview in this volume. the cause of gravity, It is interesting to note that Mill, at least, agreed with 30. For evidence that this was the tacitly accepted view, see Carpenter, I{ooirer, Wollaston, and Fawcett in this volrrme. 31. Darwin, Lile and Letters (1887), 2:6; see also Darwin (i859), p. a09. 34. Ibid., p. 48B. 32. See, for example, pictet, . the papers by Wollaston, Sedgwick, Owen, and 35. March29, 1863,Life andLetters (1887),2:202-203. Agassiz in this volume. 12,1870, More Letters (1903), l:321. 33. Darwin (1859), p. 36.July 490. 37. February18, 1860,ibid., 1:i40-141. I I

54 Darwin and His Critics

Darwin, saying, "I do not think it an objection that levolutionary theory] does not, even hypothetically, resolve the question of the first origin of life, any more than it is an objection to chemistry that it cannot analyse beyond a certain number of simple or elementary substances."3s Newton was condemned for not stating explicitly certain assumptions of his theory. Darwin was condemned for doing just the opposite (by Hop. kins, for example) . Darwin answered that "though perhaps it would have been more prudent not to have put it in, I would not strike it out, as 4'Teleology it seemed to me probable, and I give it on no other grounds."se Here was Darwin's sin: he had not exercised enough caution. Science must be safe. The inductive method was calculated to make it safe. Many scientists Teleologyhad been part of the conceptual frameworh of Western science were willing to admit that varieties may have arisen through natural selec. from ancient Greece until the time of Darwin. Natural phenomena might tion, but one must not carry things too far. These varieties never strayed be governed by scientific laws, but it was the Creator who had instituted from the confines of their species (Pictet). Or perhaps, as Forbes and ii:i them. Galileo and Newton replaced ono physical theory with another, but others suggested, there were several centers of creation, and then dispersal, irrrthey lelt the teleologicai world-picture intact. The findings of paleontologists but no evolution beyond certain bounds-say, the generic level. Like Tycho " and geologistshad necessitateda reinterpretation of Genesis. But it was Brahe's compromise between the geocentric and heliocentric systems,in lt Darrvin who finally forced scientists to realize just how trivial teleology which the sun revolved arouncl the earth while all the other known planets had become in their hands. The change in scientific thought marked by revolved around the sun, hybrid systemslike Forbes's failed to gain wide. the appearanceof the Origin of Specieswas so fundamental that it certainly spread acceptance.There was considerablewishful oratory about moderatiorr$$', s.\, deservesthe title of a conceptual revolution. The problems which arose in all things-a little bit of evolution tempered u'ith a little bit of special$]l Irorn speciesevolvine will be discussedin the next chapter. In this chapter creation, a little bit of natural selection and a little bit of divine guid- u rve will be concerned with the difFculty which scientistshad in reconciling ance-but at bottom the two positions were incompatible. As soon as a r' $^ their belief that the order in the world must be in some senseteleological natural explanation was achnowledged for the origin and evolution of some $ with their grorving awareness that the only sense in which it could be species,nothing but time stood in the way of extending it to all species, termedteleological was a trivial one. Conversely, as soon as a supernatural explanation was allowed for the origin $' of some species, there was nothing to prevent a supernatural explanationHr', Teleology,the belief that things in the empirical world "strive" to attain being given for all species.Unlike Wallace, Darwin insisted telling on a är.'K ends, is one of the most influential and misunderstood doctrines in the totally consistentnaturalistic story or none at all. $f' $i history of philosophy. In one interpretation, teleology entails a universal 38. Mill (1910),2:1Bl; seealso Fawcett in thisvolume. c.onsciousbeing ordering everything for the best. As Plato Put it: "I heard 39. December25, 1859,Lile and Letters(1887), 2:46. $, some one reading, as he said, from a book of Anaxagoras, that mind was $r'' fr the disposer and cause of all, and I was delighted at this notion, which $' appeared quite admirable, and I said to myself: if mind is the disposer, {.,' mind will dispose all for the best, and put each particular in the best $' place."1 il' For the Platonic doctrine of external teleology, Aristotle substituted the lil- subtler view of immanent teleology. For Aristotle the ends were internal [: f.. I. Plato.Plnedo. St. 96-99. fi 56 Dalwin and His Critics Teleology

to the subject' Individuals did what was best for themselvesby themselves. i ,il for regularitiesto exist. The emptinessof thesepositions is all too apparent, Every natural kind (or species) had a static, immutable essenceas rts .".but they were the positions to of formal which the proponents teleology were cause' These essencesmade a thing.lvhat ,"vas. it These essencesiu at last driven. Darwin's theory was one of the chief instruments in the turn also serwed as final and efficient ' causes. The end toward which a' final trivialization of teleology. things strove was to realize their olvn ,,[For] essenceas fully as possible. Thanks largely to the efforts of Thomas Aquinas, Aristor_elian meta- any living thing that has reached its normar development and which rs physics,physics, and natural history were incorporated into Church dogma. unmutilated, and whose mode of generation is not spontaneous,the most Tlrrough the years, however, Aristotle's metaphysics took on a decidedly natural act is the production of another like itserf, an animal producing ' Platonic caste. God was not merely a detached, impersonal first and final an animal, a plant a plant, in order that, as far as its nature allows, it may . . cause.but an overseerwho actively participated in the affairs of the world. partake in the eternal and divine. Trrat is the goal towards wrrich aI things He both instituted the laws of nature and periodically suspended them strive, that for the sake of which they do *h]tsoerrer trreir nature renders in miracles. Copernicus and Galileo had to combat the Aristotelian physics possible."z of natural place, but they did not attack either the metaphysicsor theology Both of these versions of teleology can be interpreted to be exciting, of.Church doctrine. God still instituted the laws of physics and still sus- substantive claims about the empirical world. In these interpretations they pended them on occasion, but these laws were the laws of Newton, not have been shown to be untenable. For example, accordin.gto external teleol- Aristotle. But of even greater significaflce,Newton's laws required the con- ogy, given a knowledee of the orde'ing mind, one should be abre to infer tinued and continuing efforts of God in their operation. Newton was anxious rvl-rat tl-re empirical world must be rike, ancl conversery,given knowledge to reconcile physics with theology, and his instrument was Richard Bentley of the e'rpirical world, one should be abre to infer the crraracter of the (1662-17+2).3 ordering mi'd. If the universe is a perfectly running mechanism rvith a place Bentley did for Newtonian physicswhat Aquinas had done for the physics for everything and everything in its place, rhen one type of mind is implied. of Aristotle. In "A Confutation of Atheism from the Origin and Frame If it is a shoddily constructecr mechanism which needs constant tinkering, of the World" (1693), he argued that Newtonian physics was not only another type of mind is implied. what externar tereologistsdid not rike compatible with the existence of God but also necessitatedit. Bentley's about evolutionary theory was the type of mind it irnplied. God coulcl arguments all follow the sarne format. Certain phenomena were derivable have constructed the worlcl so that species evolved by natural selection Irom Newtort's laws, e.g., the earth traveling around the sun in an ellipse. in the struggle for existence, bur that ki'd of God dicl not seem especialry Other phenomena were not derivable from Newton's laws, e.g., the sun worthy of love and veneration. Evolutionary theory had even more devastat- bcing luminiforous and the other bodies in the solar system opaque, the ing consequencesfor immanent tereorogy. If essencesare static and if in distancesof the various planets from the sun, and the inclination of the general the goal toward whicrr all things strive is to realize their esserrce, earth'saxis of rotation to its plane of revolution. Now that Aristotle's physics then the wholesale progressive change entailed by evorutionary theory is of natural place had been abandoned, these phenomena had no explanation impossible. If evolution has occurred, then either essencesare not static in terms of natural law. They had no secondary causes. They appeared or else things must strive, not to furfilr their own essence,but the essence to be "accidental" features of the universe. Yet they had to be precisely of some other species. as they were in order for the earth to support life. If the earth were Both versions of tereology also have more sophisticated interpretations, farther away from the sun, then it would be too cold to supPort life. If but with these interpretations they become vacuous. An advocate of external nearer, it would be too hot. If the earth's path had been more elliptical, teleology might be led to say that whatever the larvs of nature turn out the extremes in temperatur-eon earth as it revolved around the sun would to be' God did it' He never suspends these laws in divine intervention, be too great. If the earth's axis had not been inclined to the plane of and these laws reveal nothing of his character. An advocate of immanent its orbit, parts of the earth would be too hot to support life and others teleology might assert that all it takes for the worrd to be teleolosical too cold. If the earth revolved around the sun more slowly, the seasons 2. Aristotle,De Anima, 415" 26. 3. Lilre Whewell,Bentley was Master of Trinity College,Cambridge (1700-1742). 58 Darwin and His Critics Teleology 59

would be too long. If rnore quickly, too short. And so on. All these phe- As Aristotle observed, instead of organisms' being so well-organized and nomena had to be as they were if life-- especially man-was to exist. Their. rveli-adaptedbecause it was of their essenceto be so, "such things survived, disposition did not follow fi'om Newton's laws. Flence, either they occurred being organized spontaneouslyin a fitting way; whereas those which grew by accident or else God did it. The chance coincidence of so many phe- otherwiseperished and continue to perish." Aristotle immediately dismisses nomena was extremely implausible. Flence, God was responsible. The ex- such a ridiculous contention. "Yet it is impossible that this should be the istenceof life was good. I{ence, God was good. tlue view. For teeth and other material things either universally or nolmally- This Neoplatonic world-view was to find favor among such biologists come about in a given way; but of not one of the results of chance or as Cuvier, Owen, Agassiz, and von Baer. Space was God's sensorium, grav- spontaneity is this true."? Whenever anything occurs regularly, it must be ity his consciouswill, and each speciesa divine thought. Even an empiricist becausethe formal and final causescoincide. Becausean organism is what like Flerschel concurred in this ontology, hoping to combat the more radical it is, it produces teeth as they should be. The haphazard production of empiricism of Locke and Hume and the materialism of Laplace. According numerous alternatives and the elimination of those that are not fit occur to llerschel, falling bodies are urged .to the earth's surface ,,by a force or too irregularly to be part of the natural order. effort, the direct or indirect result of a consciousnessand a zolll existing An identical story can be told for William Whewell, with one minor someu,tlzere,though beyond our power to trace, which force we term complication. FIe somehow had to reconcile his own advocacy of final causes grauity."l with Bacon's "barren virgin" quip. Whewell's solution was to argue that In his Bridgewater Treatise, Whewell updated Bentley's arguments for final causes should be excluded from physical inquiry but were perfectly God's existence. In reading I{erbert Mayo's The Philosolthy o.f the Liuing legitimate as the results of such inquiry. Final causeswere barren because (1838), Darwin was incensed over Mayo's contention that Whewell was they themselves were the fruits of the labor.s God ordered the universe profound "because he says length of days adapted to duration of sleep according to his divine plan, and it .was the goal öf science to discover of man!!! whole universe so adapted!!! and not men to Planets.-instance this plan. Any explanation in terms of the perishing of the unfit and the of arrogance!!"5 The Bridgewater Treatises were published becausescien- survival of the fit was inconceivable: tists had been gaining the reputation of being materialists, determinists, If the objector were to suppose that plants were orginally fitted to and atheists, especially in France with the workl of D'Alembert, Diderot, yeals of various lengths, and that such only have survived to the present de la Mettrie, Laplace, and Voltaire. Whewell was pleased to do rvhat time, as had a cycle of a length equal to our present year, or one which he could to combat the growing slander by showing the mutual dependence could be accommodated to it; we should reply, that the assumption of science and religion. "My prescribed object is to lead the friends of is too gratuitous and extravagant to require much consideration.e religion to look with confidence and pleasure on the progressof the physical Lilre a true philosopher, Whewell went on to hedge his bet. Even if adzpta- sciences,by showing how admirably every advance in our knowledge of tions did come about by such a gratuitous and extravagant mechanism, the universe harmonizes with the belief of a most wise and good God.',u "it does not remove the difficulty. Ifow came the functions of plants to Periodically, proponents of teleology, whether of the immanent or tire be periodical at all?" external variety, entertained a possiblealternative explanation for the aoap- Prior to the publication of the Origitt, philosophers and scientists had tation of living creatures to their environments-the survival of the fit. I some justification for rejecting nonteleological explanations of adaptation, since there was no alternative explanation. Lamarck's theory came closest (1833), 4. Herschel pp.221-222. to supplying a mechanism fol adaptation, but few were willing to accept 5. DeBeer(1960), p. 134. 6. Whewell (1833), p. i; though Whewell'sBridgewarer Treatise was Volume it, both becauseof its own weaknessesand becauseof the inordinate influ- III of this series, it was the first to appear in print. The complete title of this ence of Cuvier. After the Origin, however, the reactions of philosophers series was TIte Bridgeuater Treatises on the Power, Wisdom and Goodness of God, as in the crcation. Dach contribution -Manifested will be cited separately by the title of that volume. We have only a fragment of Charles Babbage,i (1S37) etror* 7. Aristotle,Physics, bk. II, ch. B. which does not form a part of the Bridgewater B. Whewell(1833), p. 180. Treatises, even tho'gh it bears p. the title The Ninth Bridgeuater Treatise. 9. Ibid.. 27. 60 Darwin and l{is Critics Teleology 6i

and scientistswere not much different. Mill, inhisTlzree Essayson Religion Flerschel's position on these matters was typical. In his 1861 edition written during the decade following the publication of the Origin and of Physical Geography of tlte Globe, he added the following comment published posthumously in 1874, still found the argument from design pre- on Darwin's theory: ferable to evolution by natural selection: This was written prior to the publication of Mr. Darwin's work on I regret to say, however, that this latter half of the argument is not the Origin of Species,a work which, whatever its merit or ingenuity, we. so inexpugnable as the former half. Creative forethought is not absolutely cannot, however, consider as having disltroued the view taken in the the only link by which the origin of the r,r'onderful mechanism of the text. We can no more accept the principle of arbitrary and casual varia- eye may be connected with the fact of sight. There is another connecting tion of natural selection as a sufficient condition, per se, of the past and link on which attention has been greatly fixed by recent speculations, present organic world, than we can leceive the Laputan method of com- and the reality of which cannot be called into question, though its posing books (pushed ä outrance) as a suficient account of Shakespeare adequacy to account for such truly admirable combinations as some of and the Principia.t" those in Nature, is still and will probably long remain problematical. This is the principle of "the survival of the fittest." Herschel is repeating l-rischarge quoted earlier that Darwin's theory was Mill continues: the law of higgledy-piggledy. Evolution by random variation and natural selectiondid not exhibit the mathematical regularity and simplicity charac- Of this theory when pushed to this extreme point, all that can now teristic of physical law. The laws of physics wele worthy of God's author- be said is that it is not so absurd as it looks, and that the analogies just which have been discovered in experience, favourable to its possibility, ship, as Hamlet and Macbetlt were worthy of Shakespeareand the far exceed what any one could have supposed beforehand. Whether it Principia worthy of Newton. Darwin's theory implied a God who would wiil ever be possible to say more than this, is at present uncertain. The composea book by randomly striking the keys of a -typewriter until some- theory if admitted r.r,ouldbe in no way whatever inconsistent with Crea- thing turned out. Herschel did not want to deny that evoiution might tion. But it must be acknowledged that it would greatly attenuate the occur by law, but it had to be a la'w worthy of God. evidencefor it.ro

Darwin's arguments in the Origin are mere analogies,whereas the argument Equally in either case,an intelligence, guided by a purpose, must be con- from design r.r.asa genuine inductive argument. "In the present state of tinually in action to bias the directions of the stepsof change-to regulate our knowledge, the adaptions in Nature aflord a large balance of probabil- their amount-to limit their divergence-and to continue them in a definite means to deny the necessity ity of creation by intelligence." course. We do not believe that Mr. Darwin of such intelligent direction. But it does not, so lar as we can see, enter Many philosophers and scientists were willing to accept evolutionary into the formula of this law; and without it we are unable to conceive theory if only Darra'in u'ould admit divine providence. Without it they felt how far the law can have led to the results. On the other hand, we trapped between inexorable law and blind chance. The terminology of this do not mean to deny that such intelligence may act according to a law position varied, but the messagewas always the same. Some maintained (that is to say, on a preconceived and definite plan). Such law, stated in words, wouid be no other than the actual observed law of organic that some phenomena were lawlgoverned, other lthenomena not. Others succession;or one more general, taking the fonn when applied to our maintained that ail phenomena r,r.erelaw-governed. In either case, God own planet, and including all the links of the chain which have disap- instituted these laws and guidecl their action. A universe governed by divinely peared. But the one lalv is a necessarysupplernent to the other, and instituted law did not seem so cold and barren. Add periodic mir-aclesand ought, in all logical propriety, to form a part of its enunciation. Gr-anting the world-picture became evell rnore intimate. Lxclude God, and both this, and with some demur as to the genesisof man, we are far from the taken of this mysterious subject in Mr. accidental and larv-govemed phenomena bccame equally "accidental," given disposed to repudiate view Dar-r.r,in'sboolc.13 the peculiar telminology of the time.11

10.Mill (1969),pp. 172,174. 12. Flerschel (1861), p. 12; see von Baer's review in this volume for an expansion 11. For example, see the review by von Baer and the exchange between Mivart on this reference to Gulliuer's TraaeLs. and Wright in this volume. 13. Iferschel (1861), p. 12. 62 Dar-lvin and His Critics Teleology 63

A quick reading of the preceding paragraph might lead the reader to believe that there is a bit more interference by the Ct'eator in the con- the planets. It is only think tl.rat Flerschel is saying much more than he is. Herschel pleads for struction of each species than in the course of ou,ing to Paley and Co., I believe, that this more special interference a supplementation of Darwin's laws by some reference to intelligent dilec- is thought necessary with living bodies. But wc shall never agree, so tion, but what does he suggest?A description of phylogeny! Darwin was clor-rot trouble yourself to answer.1s at a loss as to the manner in which he could reply to criticisms such as these.The request for a law of divine providence could be taken literally, Wlren you conre to "Deification," asli yoursclf honestlywhethcr what in which case Darwin felt obligated to deny it. If God were all-good, you are thinking applies to the endlessvariations of domestic productions, rvhich man accurnulates for his mere fancy or use. No doubt these are all-knowing, and all-powerful, then one would expect that organisms would all causedby some unknown larv, but I cannot believe they were ordained tend to vary in directions advantageous to their survival. Darwin found Ior any purpose, and if not so ordained under domesticity, I can see no evidence o[ such directed variation. As far as Darwin could tell, varia- no reason to believe that they were ordained in a state of nature' Of tions were "chance," they occurred "in all directions." By .these claims course it may be said, when you l

in favor of evolutionary theory or against it, strongly supported this view and Lyell belabored Darwin with argurnents for admitting divine provr- of God's relation to natural phenomena. dence, especially with respect to man's mental and moral faculties. For Accidental occurrences could be shown not to be accidentar, either be- exarirple,Lyell hailed Wallace's suggestion that "there be a Supreme Will cause of the direct inter-vention of God or by subsuming them under law. and Power which may not abdicate its function of interference but may Pliysics since Ne*'ton had made constant inroads on the domain of the guide the forces and laws of Nature." What these men did not realize accidental, thereby limiting the need for God's direct intervention. As Mill ivas that by pushing God further and further in the background as the put it, there were two conceptions of theism, one consiste't with scie'ce, unknowable author of natural 1aw, regardlessof the nature of these 'laws, one inconsistent. "The one which is inco'sistent is the conception of a they frad prepared the way for his total expulsion. Like l{ant's Ding an God governing the world by acts of variable will. Tlie one which is con- rirlz, he was remote, obscure, unknowable, somehow underlying everything sistent, is the conception of a God governir-rg the r,vorld by invariable laws.,,1s and very important but of no conceivable consequenceto any endeavor. Darwin used this position on the relation betwee' science ancl religion 'feleological supplements were as otiose to evolutionary theory as they were in an attempt to gain a fair hearing for his theory. He prefaced the fir.st to contemporary versions of Newtonian theory. The superficiality of teleo- edition of the origin with quotations from wheweil and Bacon to the logicalclaims in a deterministic universe was not totally lost on the educated effect that no irnpediment shourd be placed in the path of scientific inquiry public. For example, one writer observed with respect to tl-rehabit of natu- because no larv could be discovered r.r'hich was contrary to God's will. In ralists to interpolate tl-reir writings with references to God: "It appears the sixth editiorr he added a third quotation to this same effect by Bishop to them that, unless they clrag the Creator into every second paragraph, Butler' All Darwin wanted to do was to extend the domain of secondary their essaywill not possessthe necessaryreligious veneering for the public causes to include the creation of species. Although in the past the creation t;ste."21 of species had been considered miraculous and outside the realm of lziw, Darwin was not impervious to the pathos in the dile-ttto which con- so had many other phenomena which had been shown to be law-governed. fronted his colleagues. Neither a world ruled by deterninistic laws nor Darwin u'as acting within the currently acceptecl tradition of expanding one in which chance played an important role seemed bearable. Even the realm of law. though Darwin had not intended to write atheistically, his theory robbed wl'rewell wanted to retain the creation of species as miraculous but he rhe traditional solution to this dilemma of all its plausibility. The closest recognized that such an explanation was not a tenet of physical science Danvin came to a resolution of the conflict between teleology and the but of natural theology.rs wheu'ell's bare recognition that the origin of facts of natural history was his suggestion that God instituted the general species was even susceptible to a naturalistiö explanatio' gave heart to larvs,whereas the details were left to chance: Lyell, who had pr-oved so uncharacteristically timid on the evoiution of species' In a letter to I{erschel, he r,r,rote, "whewell, in his excellent treatise My theology is a simple muddle; f cannot lool< at the universe as on the Inductive Sciences, aprlears to me to go nearly so far as to contem- the result of ülind chance, yet I can see no evidence of beneficent design, plate the possibility at least of the introcluction of fresh species being gov- or indeecl of design o[ any ]

left to the working out of what we may call chance. Not that this at all satisfr,esrrre.23

Bentley and whewell had argued that God had instituted natural and taken care of the details. Darwin believed that perhaps God instituted natural laws, but he could not be responsible for specific applications bot because of their triviality in some cases and because of their cruelty i .,chance" others. But it should be recalled that by Darwin meant Essences by laws not as yet known. Darwin,s solution was. a circuitous of determinism. Interpreted realistically, teleology was incredible. Given i., sufficiently sophisticated interpretation, it was of no relevance to science.2a .teleology.permeated Western thought, essentialism was even more Per' 23. Darwin, May.22, 1860,Lile and Letters (1g87). 2:105- metaphysical systems generated on the 24. The issr.reof teleology has had a recent ."r,,.jer"" brrt in entirely different . The number and variety of terris. several and biologists -philosophers have attempted to analyze ieleological and in England was staggering. Realists maintained that the systems in terms _naturalistically of genetic pl.ograms, negative feedbacL, urä so (Aris- on. SeeMayr (1961) and Canfield (1966). existed in nature, perhaps in individuals thernselves ) , or both in nature and in the mind of the creator (Neoplatonists) . ts süch as Cuvier, Owen, and Agassiz are often referred to flidealists" in this respect, but the term is not very apt. Idealism is contrasted with materialism, idealists maintaining that only ideas (material objects are just clusters of ideas), and materialists main- i: i.ng that only matter exists (minds are merely brain processes). Although and Darwin.might legitimately be called materialists, Cuvier, Owen, i:Agassiz were hardly idealists in this sense. Rather they were iderilists i,'tbesense that they tended to explain the order in nature by reference ..ideal types. In short, they wefe essentialists. As metaphysically aloof öminalists might be, they too were strongly predisposed to essentialism. iduals were the only independent existences. A scientist could divide iduals into classes as he pleased-just so long as these classes were iete. Nominalists were as much essentialists as the Aristotelians and ists, but witlout their metaphysical justification. rfihe empiricist-rationalist dichotomy cuts across the preceding distinctions. iricists maintained that all knowledge had its source in experience could be analyzed completely in terms of it. Rationalists rnaintained that sense experience played no role in the acquisition of knowledge else that truth could not be decided completely by reference to sense ience. The mind played an.active role. As'one might expect, empiricists d to be nominalists and materialists, whereas rationalists were fre- y disposed to idealism, though numerous excePtions can be found iio both generalizations. In this chapter, the effect of these metaphysicai ions on the acceptance of evolutionary theory will be traced. 6B Darwin and FIis Critics Essences 69

ls so Alvar Ellegärd (1957 and 1958) sees the disagreement over the im- an unfathomable chasm . . The universe, so far as known to us' casesof mutability of speciesas a conflict between empiricist and "idealist" philoso- t$nstitlrtecl,that whatever is true in any one case, is true in all phies of science. Although our story would be much neater if this were a certain description; the only difficulty is, to find the description' I(inds true, it is not. Empiricists and "idealists," while not equally opposed to are Classesbetween which there is an impassiblebalrier ' '"3 the concept of speciesevolving, were stili both opposed. Evolution by ran- 'fhough Mill's empiricist ontology did not directly require the existence proof dom variation and natural selection conflicted with teleology. Any evolution of discrete natural kincls, his logic of justification clid' At bottom, E' at all, regardless of the mechanism, as long as it is graduai, conflicted was suppiied by eliminative induction. "Either A, I), or C can cause to be with the essentialist notion of natural kinds-and on the necessityof such A ancl B are absent. Hence, C must cause E'" For this inference be speci- natural kinds, empiricists and "idealists" were in agreement. The doctrine r.aiid, all of the alternative causesof a certain l

be verified solely by reference to it. Rather they courd be known to be .of the permanence of species. (See the comments by CarPenter in his re- necessary truths only by intuition. The mind superinduces concepts on view.) For essentialists,such difEculties and disagreelnentswere only techni- the facts. These concepts are appropriate if they are clear and distinct cal problems to be overcome by more careful examination of the data. (the traditional rationalists' criterion) and if they fit. the facts closely (but ,There hnd to be diagnostic characters. For Darwin no such characters considerable latitude is permitted for rei4terpreting the facts to fit tlrc ex.istedfor speciesextended in time. concepts). one of the notable features of whewell's phitosophy of science Inorganic elements also, on occasion, were cited as examples of natural' is that he includes no mechanism for periodic conceptual revorutions. Ile kinds, though they ran a very poor third to those of geometry and natural seems to assume that in each area of science there will be one and only history. (See Jenkin's review.) What must be kept in mind is that for one scientific revolution and that in physics that revolution had already esentialists aLI natural l

in several important respects from species of and Newton. Mill, on the other hand, assimilated the axioms of geometry .of inorganic objects differ of chemical elements was to those of physics, and in this view, he was joined by Herschel. All were i.Flants änd animals. Earlier the transmutation ,:eOnrpar.cd but the two are very differ- inductions from experience. Certain ideas spring from experience, almost i to the evolution of species, Processes of one element into a like quantity spontaneously, iike very basic notions of space, time, and causation, but l ent. Pliysicists change a small quantity Lead and gold, defined in terms of their atomic number, they neverthelesswere empirical claims, whose truth could be decided by ' i..nianother'element. if all the lead in the universe were trans- ' scientific investigation. Kepler's laws certainly seemedstraightforwardly em- i still renrain lead and gold. Even a spot would still be reserved for lead in the pirical. A body could fulfill all the requirements for being a planet ancl -'. nruted into other elements, If eventually lead were to form once rnore, it still fail to move in accordance with l(epler's iaws, but the basic axiours ti:ni*nsification of eiements. ' and simple. The processby which a physical element of geometry seemed immune to verification or falsification by experiment vould be lead, Pure history are irrelevant to its identity. or observation.The parallel postulate for sure was thought to be a posterion, .. isgenerated and its past 'Ihe different with respect to speciesof living creatures. yet there seemedto be no way to confirm or refute it. situation is quite maintain that speciesmust be monoPhyletic. Various Although the current received doctrine in history is that no historical Biologistscommonly of have been sr.rggested,but the two most prevalent dispute should be elucidated or resolved by contrasting it with the present definitions "monophyly" are (a) a taxon is monophyletic if it is derived by descent views on the subject, it seems grossly unfair to leave the reader in the definitions single immediately ancestral species; and (b) a taxon is mono' same state of confusion in these natters as that which prevailed in the from a it is derived by descent from a single immediately ancestral nineteenth century. The question is whether the axioms of tl-reformal and phyletic if of its own or lower rank. On interpretation (a) a family is mono- empirical sciencesare self-evident truths superinduced on the facts by the täxon only if every speciesincluded in the family is derived from another mind, or truths inductively collected from the facts. For both, the answer phyletic in the family or at most one immediately ancestral speciesnot in- is neither. Both sides were mistaken, but the mistal

:r Darwin dismissedtheological explanations of the origin of speciesbecause .ntre not so much refuted by Darwin as discounted. Similarly, the theologi- they were not properly scientific. Ile also dismissed explanations in terms sal and metaphysical objections to evolutionary theory gradually subsided, of "plans," divine or otherwise. They, too, were empty verbiage. Explana- not becausetheir authors had been converted, but because no one whose tions in terms of coherence of plan had been common in biology for well matterecl was listening any more. The change can be seen in the '..bpinion over a century before Darwin, especially in the writings of ideal morphol- diserence between the aggressive confidence of Agassiz's first review of ogists like Goethe, Cuvier, Owen, and Agassiz. As long as one believed i.thr Origln ot' Species in 1860 and the petulant timidity of his final comments in God, and these plans could be interpreted literally as thoughts in the in 1874. Even in his original review of the Origin, Agassiz acknowledged mind of the creator, then such explanations had some explanatory force, ihat lome naturalists looked upon his idea of creation by God's mental but if reference to God is left out of the explanatory picture, then all that exertion as a kind of bigotry and his holding the view a sign of non is left are the plans. Rather than being explanations, the existence of such üafil)or ntentis.Fourteen years later he hardly dared mention his pet theory "plans" calls for explanation. In England, at least, Darwin's aversion to of creation by repeated acts of divine cognition. Owen went so far as to scientific explanations in terms of explicit reference to God and conformity assert that the leading naturalists of the day, referred to by Darwin as to plan was shared by a growing number of scientists.For example, Edward Sp€cial creationists, had neuer mai1.tained the view that species n'ere Forbes,e in 1854, published an explanation of the distribution of living $peciallycreated by divine action. Rather, he along with the other so-called creatures in geological time in terms of polarity, "a manifestation of force rpecialcreationists had always maintaintjd that some unknown law governed of development at opposite poles of an ideal sphere." Forbes divided geo- rhe introduction and extinction of species.Lyell, to the contrary, had the logical time into two periods-the Neozoic and Paleozoic.The distribution of candor to admit that he "formerly advocated the doctrine that species generic types then {ormed a figure eight with its constriction during the t'ere primordial creations, and not derivation."t3 FTe differed from the Triassic and Permian epochs. Although Forbes argued that this distribution catastlophistsonly in his belief that specieswere creatöd and extinguished occurred in time, the explanatory ideal plan was atemporal. To put serially,ratl-rer than in wholesalelots. Darwin's reaction to Forbes's explanation simply, it made him sick. trither Naturalistic explanations,had become the order of the day. The authors it rvas nothing rnore than a description of the distribution of generic types included in this anthology by and large agreed that scientific theories were in time or else it was lihe magnetism turning a table.1oDarwin could not to be judged only by scientific standards. Even the philosopher primed see how references to ideal plans could explain anything. To say that the b.vAgassiz for his review of the Origin, Francis Bowen, admitted "all that hand of a man or a monkey, the foot of a horse, the flipper of a seal, has been claimed for the proper independenceof true physical science,-that the wing of a bat, and so forth, have all been formed on the same ideal its conclusionsare to be tested by their own evidence, and not by their plan "is no scientific explanation."rl One of the purposes of evolutionary agreement or want of agreement with the teachings of Scripture, with theory was to provide a naturalistic explanation for such homologies.l2 reeeiveddoctrine in theology or philosophy, or with any foreign standard Modern readers of the Origin of Species tend to grow impatient with whatsoever."laLike Newton's hypothesis non fingo, this proclamation was Darwin for going to such lengths to argue against sp3cial creation and easierto declare than to implement becausethe boundaries between science, divine plans. They are no longer considered even viable candidates for philosphy, and theology began to blur when one approached the problem scientific explanations. The decision was not so clearcut in Darwin's day, of man's menta.l powers and morai nature. These faculties had always Many philosophers and some scientistsstill looked upon miracles and ideas beentl.re provinces of philosophy and theology. While perusing the following in the mind of the creator as acceptable elements in a scientific explanation, reviervs,the modern reader may be puzzled by the disproportionate attention though most scientistswere loath to discussthe issue.These "explanations" given to Darwin's explanations of the hive-making habits of bees and the slave-rnakinghabits of ants. The emphasis was not misplaced. Darwin was 9. Forbes(1854) , p.430. 10.Darwin, July 2, 1854,AIo1'e LetLcrs (1903) , l:?7. ll. Darwin(1871) , pp.3l-32. 13.Lyell (187g),p.469; seealso the reviewsof Hooker,Carpenter, Wollaston, I2, Scc llopkins, Mivart, and \Arrigbt revicws in this volume fol additional opiuions and Fawcett in this volume. of -Forbcs'sprirrciirle of polarity. 14. Bowen (1860), p. 476' 76 Darwin and His Critics Essences 77

taking his first steps toward the explanation of man's higher faculties. I-Iis but they occur rarely. Given what we know of genetics and population intentions were not lost on his reviewers. The conclusions ol true physical biology, gradual evolution is the rule. Huxley's suggestion has been taken science were to be judged only by scientific standards, but Darwin was up periodically by scientists (e.g., Goldschmidt ärrd Schindewolf). From trespassing on the property of philosophy and theology and deserved to a pulely scientific point of view there is no a priori reason {or preferring be criticized by their standards, and this authors like Sedgwick and Bowen one tylle of evolution over the other. From a metaphysical point of view, proceeded to do. In doing so, they were not intruding on the proper domain therc is. Speciation by saitation would permit the retention of the discrete-' of science. Rather, in Bowen's words, the "intrusion, if. any, comes from nessof natural kinds, a tenet central to essentialism. the other side. It is now the naturalist, the pure physicist, who, quitting Gray, Wallace, and Lyell all argued for the inclusion of some vestige his own territory, but, as he professes,still relying exclusively on physical of teleology in evolutionary theory. On this score, they were joined by evidence, seeksto build up metaphysical conclusions."l5 a host of other scientists,including Owen and Mivart. Mivart, for instance, Even after the boundary between philosophy and science was redrawn reasonedthat just as there was a principle internal to an individual organism to distinguish between psychology and epistemology, the adjustments rn rvhich determined its regular embryological development, there must also philosophy necessitatedby evolutionary theory were of the most fundamen- be a similar principle to determine the evolutionary development of species' tal hind. Either one of the chief examples of natural kinds had to be By reasoning in this manner, these scientistswere returning to something dismissed as not actually being natural kinds, or else the notion of natural like the Aristotelian notion of imrnahent teleology. In this case, however, kind had to be reworked. Some philosophers chose the forrner alternativc thc cnd was not a cyclical returning to the same type but a progression and retreated to geometry. Bos bos was not properly a natural kind. Equi- from one type to another. Darwin could find no evidence of such a directing lateral triangles were. Relativity theory drove the adherents of natural kinds internal influence and steadfastly refused to admit it. Once again, Darwin out of their last sanctuary. Some philosophers took the second alternative seemsto have been right. We now know why organisms go through their and tried to produce a metaphysics which did not depend on the essentialist regular cycles of development-the information coded in their DNA. This notion of natural kinds. The extreme difficulty of this undertaking can infonnation has been built up through eons of natural selection. No hint be seen in the development of philosophy during the last fifty years.t6 of a mechanism by which the future development of a speciesmay also Later criticisms of evolutionary theory tended to be directed at Darwin's be incorporated into this code has been discovered. The truly amazing mechanisms---chance variation and natural selection. Perhaps speciesevolved feature of Darwin's intellect was the frequency with which he was able and a naturalistic mechanism is called for, but Darwin's explanation was to "guess" correctly, even though he iacked the requisite data and anything inadequate. The two modifications of evolutionary .theory most frequently like an adequate theory governing the phenomena. Modern evolutionary suggested were the substitution of evolution by saltation for Darwinian theory is closer to the original Darwinian formulation today than it has gradual evolution and the addition of a force or principle internal to or- ever been.18 ganisms to direct them in their evolutionary development. The former served to salvage the discreteness of natural kinds, the latter to save lB. PeterVorzimmer (1970) comesto conclusionswhich are almostdiamerically opposed to those expressedin this Introduction with re5Jardto Darwin's adherence teleology. to gradual evolution and innate directive forces. Vorzimmer thinks that Mivart's Even Darwin's strongest supporters took great pride in keeping one toe criticisms of Darwin's theory "had been the prime instrument in badgering the elderly Darwin into the state of frustrating confusion which marked him on the dry. Huxley, for example, thought Darwin had loaded himself "with an cve of his retirement" (p. 250). See the discussion of Mivart's review of The unnecessary difficulty in adopting Natura non facit saltum so unre- Descent of Man (1871.) in this volume for further examination of vorzirhmer's servedly."rz By and large, Darwin was right. There are genetic mechanisms analysisof the situation. which result in new species' evolving in a single generation (polyploidy),

15.Ibid.,p.447. 16.D. L. l-lull (1974). 17.L. Huxley (1902), p. I89. Douglasf. Futuyma StateUniversity of NewYork at StonyBrook Evolution '! $ "'ii e : -, .. ,;f**,* o; ,, lii$, ü*"')l:1$äffiffiÄffiLÄT -'-,, "üHä-11Tffi.sffi.*:.-_ _* * _ä= illd;** "' :;,=ff,f b tr ääHffH:

Chapter19 (Evolutionof Genesand Genomes) by ScottV.Edwards, Harvard lJniversity

Chapter20 (Evolutionand Development) by Iohn R. True,State University of NewYork at StonyBrook

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Sources of the scientists' photographs appearing in Chapter I are gratefully acknowledged: Q. Darwin and A. R. Wallace courtesy of The American Philosophical Library R. A. Fisher courtesy of Joan Fisher Box J. B. S. Haldane courtesy of Dr. K. Patau S.Wright courtesy of Doris Marie Provine ' t 'J E. Mayr courtesy of Harvard News Service and E. Mayr . '-- " G. L. Stebbins,G. G. Simpson, and Th. Dobzhansky courtesyof G. L. Stebbins ,*--l- M. Kimura courtesy of William Provine

Übersetzer Andreas Held

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Kapitell ' Evolutionsbiologie1 17 Kapitel2:, DerStammbaum des Lebens: Klassifikation und Phylogenie Kapitel3: Evolutionsmuster43 Kapitel4,' Evolutionin denFossilbelegen 67 Erde91 Kapitel5" EineGeschichte des Lebens auf der Kapitel1,;, DieGeographie der Evolution 117 KapitelT, DieEvolution der Biodiversität 139 KapitelS DieEntstehung der genetischen Variabilität 161 -, Kaprtelg ' Variabilität189 Kapitella'. GenetischeDrift: Evolution nach dem Zufallsprinzip 225 KapitellI , NatürlicheSelektion und Anpassung 247 : Kapitel12 Diegenetische Theorie der natürlichen Selektion 269 Kapitell:J" DieEvolution phänotypischer Merkmale 297 Kapitel14 ' Konfliktund Kooperation 325 Kuoitel15 ',Arten353 Kapitel16 Artbildung379 KapitellT Fitness:Fortpflanzungserfolg a05 KapitellB Coevolution:Die Evolution von Wechselbeziehungen zwischenArten 429 Kapttellg DieEvolution von Genen und Genomen 449 Kapitel20 Evolutionund Entwicklung 473 Kapitel2t Makroevolution:Evolution oberhalb der Artebene 501 Kapitelz2 Evolutionswissenschaft,Kreationismus und Gesellschaft 523 EVOLUTIONARY BIOLOG I ,

a1l sorts (especially on plants) and to publish many more alticles and books, of which The Dcscent of Man is the most renowned. Darwin's books reveal an irrePressibly inquisitive rvissbegierig man, fascinated with all of biology, creative in devising hypotheses and in bringing evi- Erstelien dence to bear upon them, and profoundly aware that every fact of biology, no matter how seemingly trivial, must fit into a coherent, unified understanding of the world.

Darvvin's Evolutionary Theory TIrcOrigin of Specieshas two major theses.The first is Darwin's theory of descent with modification. It hoids that all species,living and extinct, have descended,without inter- Unterbrechung ruption, from one or a few original forms of life (Figure 1.3B).Species that diverged from a common atcestor were at firSt very simila-5,but accumulateddifferences over gleat SPans of time, so that some are now radically different frorn one anothel Darwin's concePtion of the courseof evolution is profoundly different from Lamarck's, in which the concept of common ancestrvplays aimost no role' Abstammuirg The second theme of Tfte Origin of Speciesis Darwin's iheory of the causal agents of evo- Ursachen lutionary change.This was his theory of natural selection:"if variations useful to äny or- eanicbeing ever occul assuredlyindividuals thus characterisedwill have the best chance äf b"irrg pieserved in the struggle for life; and from the strong principle of inheritance, thesewill tend to produce offsPdng similarly characterised'This principle of peqqve: Nachkommer / Erhaltrurg, I(on- don, or the survival of the fittest, I have called natural selection."This theory is a vaRla- servierung .,,Variationstheorie"

Transfornational evolution Generation I Generation 2 Generation 3 Reproductive Birth (B) age (RA) BR,\B RA O--+C O+O O +O OO O +O O +O Time+ Vuiational evolution Generation I Generation 2 Generation3 Reproductive Birth (B) age(RA) B RAB o + O------*O + O ------O o +C------O + ,--@ @ tle + q -::l--> 6 o c (D

tlme+

Figure 1.4 A diagrammatic contrast between transformational and variational theories of change,shown across three generations. Within each generation, individuals are ::_olutior,talyrepresented earlieiand later in their liver]Th" i.tdiridrr^ls in the leit column in each ge-neration [Spalte] are the olfspring of thosein the right column of the preceding gen- eration' Ivoihärgehen.tl In transfo.maüonai evolutiory indiviäuals are altered a'uring the"ii lifetimäs, and-tfreir F^t:"qT{ [N.achkonrmen]are born wiih these alterations. In variatiorial evolution, hereditarily . l:t:,',t::! liffutent forms at ihe beginning of the history are not transformed, but instead diffär rt survlval and reproductive one rate-flrortp;lanzungsrate], so that their proportions change from generaHonto änother. CHAPTER1

,,Transf orrnationstheorie" noN+L of change, diffeling profoundly T.rEoBy fiom Lamarck's TRANSFORMATTONALrFrF^D,, in which individual oiganisms chänge (Figur.e i,4). what is often called "Darwin's theory of evolution" actually includes five theories (Mayr 1982a):

Aussage, BeJrauptung 7,'Eaolution as such is the simple plapgqtig4 that the characteristics of lineages of or_ garusrns change over time. This idea was not original with Dar\f in, but iiwas Dar- erstellte win who so convincingly marshaled the evidence for evolution that most biologists soon accepted that it has indeed occurred. 2. Conmton descentis a radicaliy different view of evolution than the scheme Lamarck had proposed (see Figure 1.3). Dar-win was the first to argue that species had di- verged from common ancestors and that all of life could be portrayed as one grear family tree. Craclualisrnus 3. Qls!'tglhuis Darwin's proposition that the differences between even radically dif- ferent organisms have evolved incrementally, by srnall steps through intermediate Spt'tirrge/ Saltationen forms. The alter.ative hypothesis is that large diffe'ences evolve by leaps, or sALrA- Zrryisclrenstnfen ttoNs, r,t'ithout intermediates. 4. Populational clmnge is Darwin's thesis that evolution occurs by changes in the pro- portions of individuals within a population that have different inherited charaCteris- tics (see Figure 1.48). This concept was a completely original idea that contrasts both with the sudden origin of new species by saltation and with Lamarck,s ac- count of evolutionary change by transformation of individuals. 5. Natural selection was Darwin's brilliant hypothesis, independently conceived by ii Wallace, that changes in the proportions of different types of individuals are caused by differences in their ability to survirze and reproduce-and that such changes re- r1 anPassel-r sult in the evolution o{ adaptations, features that appear "desigrred,, to fit organ- isms to their environment. The concept of nafural selection revolutionized nöt only biology, but Western thought as a whole.

Abkörnrnlinse Darwin proposed that the various descendants of a common ancestor evolve different adaptiv features beiauie they are adapfive .-a"t atff"t'"t-rt "conditions of life"-different habitats Lebensgewohnherten 7 or habits. Moleovel, the pressure of competition favors the use of different foods or habi- I(onknlrenzdruck tats by different species- He believed that no matter how extensiveh' a species has d! verged from its ancesto{, new hereditary variations continue to arise, sothat given enough Divcrgerrz,Arr passurrgsu nter- time, there is no evident limit to the amount of diversence that can occur_ . schiede Lücke Where,thougtu do these heredituty variutio.ri.oil f.om? This was the grear ggp in Danrrin's theory and he never filled it. The problem was serious, beca,rse accoidinglo the vorherrschend / Vererbrrrrgquanti- prgvail!4g belief in BLENpTNcrNHERrrANcE, variation should decrease, not incre4se. Because tativer Melkmale / abnehmen offspring are often intermediate between their parents in features such as color or size, it was widely believed that characteristics are inherited iike fluids, such as different colors Vermisclrer.r of paint. Blending white and black paints produces gray, but mixing fwo gray pairts does- n't yield black ol white: variation decreases. Darwin never knew that Gregor Mendel had partikuläre Verelbrurg irr fact solved the problem in a paper published in 1865. Mendel's theorli of pen:rrculars INHERITANCEproposed that inheritance is based not on blending fluids, but on particles überdauerrr that pass unaltered from genelation to generation-so that variation can pers:is.!.The co.t- cept of "mutation" in such particles (later called genes) developed only after 1900 and was not clarified until considerably later.

EvolutionaryTheories after Darwin

Altlrough Theorigin of speciesraised enormouscontroversy, by the 1870smost scien- folgte tists acceptedthe historical reality of evolution by common descent.There ensued, in Paläontologre / r'erg;leicher-rde the late nineteenth and early twentieth centuries,a "golden age" of p4lepqlqlegy, com- Morpirologie parative morphology, and comparativeembryology, during which a great deai of in- Fossilbelege,Fossilfunde formation on evolution in the fossilrecord and on relationshipsamong organismswas amassed.But this consensusdid not extend to Darlsin's theorv of the causeof evolu-

adaptation Anpassung, Adaptation / environment Umwelt EVOLUTIONARYBIOLOGY 9 tion, natural selection.For about 60 yearsafter the publication of TheOrigin of Species, ali but a few faithful Darwinians rejectednatural selection,and numerous theorieswere proposedin its stead.These theories included neo-Lamarckiaryorthogenetic, and mu, iationisttheories (Bowler 1989). Nro-LevlqncrrsM [Neolamarckismus] includes severaltheories based on the old idea of inheritance of modifications acquired during an organism's lifetime. Such modifica- tions might have been due, for example,to the direct effect of the environment on devel- opment (as in plants that develop thicker leaves [Blätter] if grown in a ho! dry environ- ment). In a famous experiment, August Weismann cut off the tails of mice for many generationsand showed that this had no effecton the tail length of their descendants.Ex- iensive subsequentresearch has provided no evidence that specific hereditary changes can be induced by environmental conditions [UrnweltbedingungenJ under which they wouid be advantageousIvorteilhaft]. Theoriesof oRtHocrNnsIsIOrthogenese, Orthoevoh-rtion], or "straight-line evolutiory" held that the variation that arisesis directed towald fixed goals,so that a speciesevolves in a predeterrnined[vorherbestimmt] direction without the aid of natural selection.Some paleontoiogistsheld that such trends need not be adaptive and could even drive species toward extinction IAussterben]. None of the proponents [Befüru.orter] of orthogenesis ever Proposeda mechanism for it. Mureuomlst theories fMutationstheorien,Mutationismus] were advancedby some geneticistswho observedthat discretelydifferent new phenotypes IPhänotypen]can ariseby a processof mutation. They supposed that such mutant forms constituted new species,and thus believed that natural selectionwas not necessaryto accountfor the origin of species.Mutationist ideas were advancedby Hugo de Vries,one of the biol- ogistswho "discovered" Mendel's neglected paper in 1900,and by Thomas Hunt Mor- gan,the founder ol Drosophilagenetics. The last influential mutationist was Richard Goldschmidt (7940),an accornplished geneticist who neverthelesserroneously argued that evolutionary change within speciesis entirely different in kind from ihe origin of new speciesand higher taxa [(Taxa;Singular: Taxon)].These, he said, originate by sud- den, drastic changesthat reorganize the whole genome. Although most such reorgan- izationswould be deleterious [nachteilig], a few "hopeful monsters" would be the pro- genitors [Vor1äufer'.]of new groups.

TheEvol utionary Synthesis

Theseanti-Darwirrian ideas were refuted [widerlegt, angefochten]in the 1930sand 1940s by_the evolutionary synthesis or modern syntheiis, foiged from [geformt aus] the con- ki-butions of geneticists,systematists, and paleontologistswho reconciled [abglicheryab, stimmtenl Danrrin's theory with the facts of genetics(Mayr and provine 1980;smocovi- tis 1996).Ronald A. Fisherand JohnB. s. Haidane in Englandand sewall wright in the unitedstates.developed a mathematicaltheory of population geneticsIpop*ulations- genetikl,which showed that mutation and nafural seleciion togethercause idaptive evo- lution: mutation is not an alternative to natural selectiorybutls rather its raw material. tqov Ih: of geneticvariation and changein natural populations was pioneeredin Rus- sia by sergeichetverikov and continueä by Theodosius Dobzhansky,who moved from Russia to the united states.ln his influential book Geneticsand theorigin of species(1937), conveyed the ideas of the population genericiststo other*bioiogists,thus in- ?-*l*tlyttuT:*t their appreciationof the ge.,eti. busis of ävolution. *.uio. contributors ,_Y:1". to the synthesisincluded the zoologists Ernst Mayr, in Sys- O.rigittof (1942), iT,:i::::!,the Species andBernhard Rensch, in EuorutionAboae'the Species tne b-otanist plants :"j',Lt^"rJ, G. Ledyard Stebbins,inVariation and Eaobttionin (1950); lil $-eut"ontologistGeorge Gaylord Simpson, tnTempo and Mode in Euolution\1944) l\..rchLntccr.J,Th'e Major Fe'attLresof Eaolution (1953). These authors ar- öqculll^t'l^t_T*ttor Persuasivelythat mutation, recombination, nätural selection,and other processes sEWALLWRIGHT lo CHAPTER1

ERNSTMAYR G. LEDYARDSTEBBINS, GEORGE GAYLORD SIMPSON, AND THEODOSIUSDOEZHAN5KY

openttnsToithin species(which Dobzhansky termed microevolution) account for the ori- gin of newspecies atxd for themajor, Ionglerm t'eatures of eaolution(termed macroevolution). Fundamentalprinciples of evolution The principal claims of the evolutionary synthesis are the foundations of modern evo- ;:: lutionary biology. Although sorne of these principles have been extended, clarified, or modified since the 1940s,most evolutionary biologists today acceptthem as fundamen- stichhaltig ta1ly valid. These,thery are the furdamental principles of evolution, to be discussedat t length throughout this book. $ Genotyp 1. Thephenotype (observed characteristic) is dffirent ftom theK!\fupg(the set of genes in an individual's DNA); phenofypic differencesamong individual organisms may zurückzufuhren be due partly to genetic differencesand partly to direct effectsof the environment. Cene 2. Environmental effectson an individual's phenotype do not affect the genespassed on to its offspring. In other words, acquiredcharacteristics are not inherited. behaiten 3. Hereditary variations are based on particles-genes-that retain their identity as they passthrough the generations; they do not blendwith other genes.This is true of both Merkmale discretely varying traits (e.g.,brown vs. blue eyes)and continuously varying haits (e.g.,body size, intensity of pigmentation). Genetic variation in continuously vary- ing traits is based on severalor many discrete,particulate genes,each of which af- polvgene Vererbtmg fects the trait slightly ("polygenic inheritance"). 4. Genesmutate, usually at a fairly low rate, to equally stable altemative forms, Allele known as alleles.The phenotypic effect of such mutations can range from unde- verstärkt / Rekombination tectableto very great.The variation that arisesby mutation is amplified by recom- Genorte, Genloci (Singular: Genlocus) bination among allelesat different loci. bedingt, hat zur Folge 5. Eaolutionarychange is a populationalprocess: it entails,in its most basic form, a Frequenzen, Häufigkeiten changein the relafive abundances(proportions or .frequencies)of individual organ- isms with different genotypes (hence, ofteru with different phenotypes) within a population. One genotype may gradualiy replaceother genofypesover the course Vpr',lränor'-'_-*"ö*-'ö rno of generations.Replacement may occur within only certain populations, or in all the populations that make up a species. 6. The rate of mutation is too low for mutation by itself to shift a population from one genotype to another.Instead, the changein genotype proportions within a popula- zufällig tion can occur by either of two principal processes:random fluctuations in propor- genetischeDrift, Gendrift tions (geneticdrift), or noruandom changesdue to the superior survival and/or re- production of some genotypescompared with others (i.e.,natural selection). Natural selectionand rarrdom genetjc drift can operate simultaneously.

macroevolution Makroevolution / microevolution Mikroevolution EVOLUTIONARYBIOLOGY 11

7. Even a slight intensity of natural selectioncan (under certain circumstances)bring about substantial evolutionary changein a realistic amount of time. Natural selection cannccount for bothslight andgreat dffirences among species, as well as for the earliest stagesof evolution of new traits. Adapiations are haits that have been shaped by nafural selection' 8. Natural selectioncan alter populations beyond the original range of variation by increasingthe frequenclr of allelesthat, by recombination with other genesthat af- Allelfrequenz fect the sametrait, give rise to new phenotyPes. 9. Natural populations are geneticallyvariable, and so can often evolve rapidly when environmentalcondi tions change. 10. Populationsof a speciesin different geographic regions differ in characteristicsthat have a geneticbasis' 11, The differencesbetween different species,and between different populations of the samespecies, are often based on differencesat severalor many genes,many of which have a small phenotypic effect.This pattern supports the hypothesis that the differencesbetween speciesevolve by rather small steps. 12. Differencesarnong geographic populations of a speciesare often adaptive, and thus are the consequenceof natural selection. 13. Phenotypically different genotyPesare often found in a single interbreeding popu- sich unteleinander kreuzend lation. Speciesare not defined simply by phenotypic differences.Rather, different speciesrepresent distinct "gene pools"; that is, speciesare grouPs of interbreeding Genpools oi potentially interbreeding individuals that do not exchangegenes with other such glouPs. 14. Speciationis the origin of two or more speciesfrom a single corrunon ancestor.Spe- Artbildung, Speziation ciation usually occursby the geneticdifferentiation of geographically segregated Differenzierung / getrennt populations.Because of the geographic segregation,interbreeding does not prevent incipient geneticdifferences from developing. einsetzend,begimend. 15. Among living organisms,there are many gradations in phenotypic characteristics among speciesassigned to the samegenus, to different genera,and to different Gattung families or other higher taxa. Such observationsprovide evidence that higher taxa ariseby the prolonged, sequentialaccumulation of small differences,rather than by the sudden mutational origin of drastically new "type-s." Entstehung 16. The fossil record includesmany gapsamong quite different kinds of organisms.Such gapsmay be explainedby the incompletenessof the fossil record.But the fossil recordalso includes examplesof gradationsfrom apparently ancestralorganisms to quite different descendants.These data support the hypothesisthat the evolution of large differencespISg994Cl4Ie!qC!tA!y. Hence the principles tha! explain the evolu- schreitet stufenweise voran tion of populationsand speciesmay be exhapolatedto the evolution of higher tara. _'"-_'ö-_--__'--hnchoererhnpf

EvolutionaryBiology sincethe Synthesis Sincethe evolutionary synthesis,a great deal of researchhas elaboratedand testedits ba- sic principles.Beginning in the 1950sand accelerating [sich beschleunigend] since, ad- vancesin geneticsand molecular biology have virfually revolutionized the study of evo- l"jt9" and have opened entirely neü research areis, such as molecular evolution. Molecularbiology has provided täob for studying a vast number of evolutionary topics, lucl3s mutation, geneticvariatiory speciesdifferences, deveiopment, and the phyloge- netrchistory of life. S,il.: . the mia-lSOOs,evolutionary theory has expanded into areassuch as ecology,an- imal behavior,and reproductive biology, äna detäitea theories have been develolld to explain the evolution äf particulur Una!äf characteristics such as life span, ecologiial dis- $b1dory and social behävior. The study of *uo*"of"Uon has been renewed byfrovoca- ., , I":t^l*:Oretations of the fossil record und by ,,"* methods for studying phytogeneticre- illl-Thpt IstamnresgeschichtlicheVerwandischaftsbeziehungen]. ai methods mo." . sophisticatedand available,virtually new"fieids of-ät"."tui evolutionary study HLl1":"lenavedeveloPed. Ambng thesefields is Hlor-scuranEvoLUTroN Imolekulare Evolution] MOTOO KIMURA 12 CHAPTER1

Nerr tralther:rie (analyses der molektrlaren of the processesand history of change in genes), in which the xsurnaL rHeoo,, Evoh-rtion, Mutationstlreone oF MoLEctr-AR EvoLUTIoNhas been particularly important. This hypoihesis, develope4 qs- pecially by Motoo Kimura (1924-7994), holds that most of the evolution of Di\A s;_ evoluti or1äreEntwicl

Philosophicallssues

Foleen,Ausrvirkurrgen Thousands of pages have been written about the pl-rilosophical and social implications of evolution. Darwin argued that every characteristic of a species can vary and can be alteied :1,: i;l lehnte alr radicaily, given enough time. Thus he reiccled the essentialism that western philosophy had inherited from Plato and Aristotle 1;.,l and put variation in its place. Darwin also helpeä {i.. to replace a static conception of the n'orld-one virtually identical to the Creator's perfect ,it r endlos creation-with a world of ceasglesschange. It was Darwin who extended to living things, t::: Stasis including the human species, the principle that change, not stasis, is the natural order. Above all, Darwin's theory of random, purposeless variation acted on by blirrd, pur- 't, poseless natural selection provided a revoiutionary new kind of answer to almost all ques- tions that begin with "Why?" Before Darwiry both philosophers and people in general i{ \i answered "Why?" questions by citing purpose. Since only an intelligent mind, with the capaci{z for forethought, can have purpose, questions such as "Why do plants have flow- Erdbeben ers?" or "Why are there apple trees?"-or diseases, or eartlrquakes-were answered by Zweck imagining the possible puIpgEC that God could have had in creating them.'Ihis kind of überflilsr1t explanation was made completely supelfluous by Darwin's theory of natural selection. The adaptations of organisms-long cited as the most conspicuous evidence of intelligent design in the universe-could be explained by purely mechanistic causes. For evolution- ary biologists, the flower of a magnolia h as a function, but not a purpose.it was not de- r.ermehren signed in order to pgqp_Agatethe species, much iess to delight us with its beauty, but in- stead came into existence because magnolias with brightly colored flowers reproduced ft'uchtbar; produktir, / r'erunsi chernd more p1q1if4e1b than magnolias r.rrith less bdghtiy colored flowers. The unsettling im- plication of this purely material explanation is that, except in the case of human behav- ior, we need not invoke, nor can we find any evidence for, any design, goal, or purpose anywhere in the natural world. It must be emphasized that all of science has come to adopt the way of thought that Darwin applied to biology. Astronomers do not seek the purpose of comets or supemovat Wasserstoffbrirckenbindungen nor chemists the purpose of hydrogen bonds. The concept of purpose plays no part in sci- entific explanation.

Ethics,Religion, and Evolution

ln the world of science, the reality of evolution has not been in doubt for more than a hun- dred years, but evolution remains an exceedingly controversial subject in the United States and some other countries. The creationist movement (creatonism) opposes the teaching of evolution in public schools, or at least demands "equal time" for creationist beliefs. Such opposition arises from the fear that evolutionary science denies the existence of God, Handehr and consequently, that it denies any basis for rules of moral or ethical conduct. Our knowledge of the history and mechanisms of evolution is certainly incompatible u'örtliclr with a literql reading of the creation stories in the Bible's Book of Genesis, as it is incom- patible with hundreds of other creation myths that people have devised. A literal reading of some passages in the Bible is also incompatible with physics, geology, and other natu-

creationist movement (creationism) kreationistischeBewegung (Kreationismus) 524 CHAPTER22

TheEvidence for Evolution

The evidence for evolution has been presented throughout the preceding chapters ot this book. The examples provided represent only a very small percentage of the stud- ies that might be cited for each particular line of evidence. In this section, we will sim- ply review the sources of evidence for evolution and refer back to earlier chapters for detailed examples.

The fossil record i 1r:-rri'"]"1-" The fogsil rqqarci is extremely incomplete, for reasons that geologists understand well (see i_ jrt ii_t.til.:.:a:rijtt I) Chapter 4). Consequently, the transition4l qlaggg that we postulate in the origin of many higher taxa have not (yet) been found. But there is absolutely no truth to the claim, made by many creationists, that the fossil record does not provide any intermediate forms. There are many examples of such forms, both at low and high q1o4g,4q!qlCv_ql9; Chapter 4 pro- vides several examples in the evolution of the classesof tetrapod vertebrates.Critically important intermediates are still being found: just in the last few years, several Chinese fossils, including feathered dinosaurs, have greatly expar-rdedthe record of the -origin of birds. The fossil record, moreovet docurnents two important aspects of character evolu- tion: mos4lc ey_Sl1-tigl(e.9., the more or less independent evolution of different features in the evolution of mammals) and gladual change of individual features (e.g., cra11allu - paerty and other features of hominins). Many discoveries in the fossil record fit predictions made based on phyiogenetic or other evidence. The earliest fossil ants, for instance, have the lyqAplike features that had been predicted by galsrl1olagiet_s,and the discovery of feathered dinosaurs was to be ex- pected, given the q!4qq4ruq that birds are modified dinosaurs. Likewise, phylogeneiic analyses of living organisms imply a sequence of branching events, as well as a sequence of origin of the diagnostic characters of those branches. The fossil record often matches

i! Jli'iI \ |LI Ll: the predicted sequences(as we saw in Chapters 4 and 5): for example, prokaryotes plg qgde eukaq/otes in the fossil record, wingless insects (the phylogenetically basal bristle: tails) precede winged insects, fishes precede tetrapods, amphibians precede amniotes, al- gae precede vascular plants. ferns and "gyll4Alpglalq" precede flowering plants.

Phylogenetic and comparative studies ,:, ..iri.l',1ii,ir. \,.;r,. r:.ii- Although many uncertainties about pfrylogsletLqfcleüS4üpg persist (e.g., the blanch; ., I'.Iirri-.,, i.tL;i;r',ri,riiI,, 4.!g_aldcl of the major groups of birds), phylogenies that are well supported by one class rl,.rr \ r'l /,.\ i:.]tilll of charactersusually match the relationships implied by other evidence quite well (see '..'l'- i..i.rl.'r.: |ii, llir'l;t rl Chapter 2). For example, 14qle_rrl4lphyle€enleg support many of the relationships that have long been postulated from morphological data. These two data sets are entirely in- dependent (the molecular phylogenies are often based on sequencesthat have no bio- Iogical function), so their correspondencejustifies confidence that the relalionships are | | :i:::,--ttt-r:r il l real: that the lirya&eq form glogplrylejiSg{o,Up! and have indeed descended frorn com- mon ancestors. The largest monophyletic group encompassesall organisms. Although Darwin allowed that life might have originated from a few original ancestors, we can be confident today that a1lknown living things stem from a single ancestor because of the many features that are universally shared. These features include most of the qoda4g in the genetic code, the ". t:. li it:- r'- lit'i::i1l,r:rr| machinery of nqelel! 4c1dre+liealis4, the mechanisms of transcription and translation, ti,.:tl .i'; -ifrirr.'i proteins composed only of "left-ha_nded" (t=:qqnq) amino acids, and many aspects.ol fundamental biochemistry. Many genes are shared among all organisms, including ihe J'i, lr !_,, three major l'empires'1 (Bacteria,Archaea, and Eukaryota; see Chapters 4 and 19), ana these genes have been successfully used to in{er the deepest branches in the tree of life. rir\:,ll.il $+cteaaliltc have shown that the differences among rc]4lcd species often form grac- ual series, ranging from slight differences to great diffärences with stepwise intermedi- ates (e.g.,Figure 3.21).Such intermediates often make it difficult to establisl-rclear-cut fam- lrr.ir lr, lr ilies or other higher taxa, so that classification often becärmesa somewhat,4!i1r44y cloice between "splltting" species among many taxa and "lumping" them into ferv. Systemanc EVOLUTIONARYSCIENCE, CREATIONISM, AND SOCIETY 529

studies have also demonstrated the common origiry or hSglo_bry, of characteristics that Hrtmolirqie may differ greatly among taxa-the most familiar examples being the radically differ- ent forms of limbs among tetrapod vertebrates. Homology of stmctures is often more ev- ident in early developmental stages than in adult organisms, and contemporary dgyelqg Enth'icl

Genes and genomes The revolution in molecular biology and genomics is yielding data about evolution on a Centrnrik Iarger scale than ever before. These data increasingly show the extraordinary commonal- Ccmeirrsamkcit {y of all living things. Because of this commonality, the structure and function of genes and genomes can be understood through comparisons among species and evolutionary models. (Indeed, it is only because of this common ancestry that there has ever been any gemeins.rnreAbstamnr Lr ng reason to think that human biochemistry, physiology, or brain fr,rnctiorymuch less genome function, could be understood by studying ygeqt flies, rats, or cats!) Molecular studies show that the genomes of most organisms have similar elements, such as a great abundance of noncoding pseudogenes and satellite DNA and a plethql4 nichtcoclierenrlci'ser-r rlogene / of "selfish" transposable elements that generally provide no advantage to the organism. Satelliten-D\A / I'aille.,,eeoisti- These features are readily understandable under evolutionary theory, but would hardly sche" translronierbarcElcmenle i be expected of an intelligenf omnipotent designer. Molecular evolutionary analyses have ;r1lrnäcl'rtig shown in great detail how new genes arise by processes such as unequal crossing over, ungleichesCrossing-over and how duplicate ge4Cqdiverge in functiory increasing the genetic repertoire (see Chap- d r,rpiizii..rteOc.ne ter 19). Some DNA polymorphisms are shared between species,so that, for example, some Polvrnorphismen maior histocompatibi of humans are more similar and more closely related Haupt-Flistokornpa tibi litäts- to chimpanzee sequencesthan to other human sequences(see Figure 12.238).What more St-qutnze n striking evidence of common ancestry could there be? Among the many other ways in which molecular studies affirm the reality of evolu- tion, consider just one more: molecular clocks. They are far from perfectly accurate, but mLrlekul.rreUhlr-.n sequence differences between species nevertheless are roughly correlated with the time since common ancestry, judged from other evidence such as biogeography or the fossil phg4q I i,r f.'r* h i,., 1 record (see Chapters 2'and 4). The sequence differences do not simply encode the '.1,-i.,rh,'ri.,-1.,. typlgd{fele4gq that the organisms manifest, and the phenotypic differences themselves are much less correlated with time since common ancestry No theory but evolution makes sense of these patterns of DNA differences among species.

Biogeography We noted in Chapter 6 that the geographic distributions of organisms provided Darwin VerLrreitrrngen with abundant evidence of evolutiory and they have continued to do so. For example, the distributions of many taxa correspond to geolbgical events such as the movement-of land masses and the formation and dissolution of connection.sbetween them. We saw that the Auflirsr-rng phylogeny of Hawaiian species matches the sequenceby which the islands came into ex- istence.We saw that diverse ecological niches in a region are typically filled not by the irkologischt Niscl-ren same taxa that occupy similar niches in other parts of the world, but by different mono- r-nouophr')eti schc. Cn-r pp.erl phylg!4€Iqqp! that have undergone independent adapl!vg_I44i41iq4 (such as the anoles adaptrrc R.rctatiou of the Greater AnLilles). We sary as did Darwin, that an isolated region such as an island GnrßeAntillen is not populated by all the kinds of organisms that could thrive there, as we might sup- pose a thoughtful designer could arrange. Instead, whole groups are commordy missing, and human-introduced species often come to dominate.

Failuresof the argument from design Since God cannot be known directly, theologians such as Thomas Aqqtleq have long at- Thomas von Acltrin tempted to infer His characteristics from His works. Theologians have argued, for in- , stance, that order in the universe, such as the predictable movement of celestial bodies, Himnrelskörper- implied that God must be orderly and rational, and that He created according to a plan. From the observation that organisrr's have characteristicsthat sewe their survivaf it could t: 7 53() CHAPTER22

tvohh'oIIeurl similarly be infefred that God is a rationaf intelligent designer who, furthermore, is benef- Segen icent: He not only conJerred on living things the boon of existence,but equipped them for all their needs. Such a beneficent God would not create an imPerfect world; so, as the philosopher Lerbniz said, this must be "the best of all possible worlds." (Leibniz's posi- gnarlenlosausgelacl-rt tion was actually more complicated, but his phrase was mercilessly ridiculed by Voltaire in his marvelous satire Candide.)The adaptive design of organisms, in fact, has long been Antrieb cited as evidence of an intelligent designer. This was the thrust of William Paley's (1831) famous example: as the design evident in a watch implies a watchmaker, so the design Desigr.rargurlen t evident in organisms implies a designer of life. This "argument from design" has been re- newed in the "intelligent design" version of creationism, and it is apparently the most fre- quently cited reason people give for believing in God (Pigliucci 2002). Of course, Darwin made this particular theological argument passd by providing a nai- ural mechanism of design: natural selection. Moreoveq, Darwin and subsequent evolu- tionary biologists have described innumelable examples of biological phenomena that are hard to reconcile with beneficent intelligent design. just as Voltaire showed (in Can- Falce, Cegenstanclrles Spottes dide) that cruelties and disastersmake a mockery of the idea that this is "the best of all possible worlds," biology has shown that organisms have imperfections and anomalies Eventualitäten that can be explained only by the continggnclg! of history, and characteristics that make sense only if natural selection has produced them. If "good design" were evidence of a kindly, omnipotent designel, would "inferior design" be evidence of an unkind, incom- petent, or handicapped designer? rutli urc.ntärc(r'erkii urr-nerte)Organe Only evolutionary history can explain vestigial organs-the rudiments of once-func- Bt'cken / Obc.rschenkelknocher.t tional features, such as the tiny, useless pelvis and femur of whales, the reduced wings venvachscne Fliigeldecken / funk- under the fused wing covers of some flightless beetles, and the nonfunctional stamens or Iior.rs]oseStatrbblätter ocler Stempel pistils of plants that have evolved separate-sexed flowers from an ancestral hermaphro- r getrr.lrnteeschltchtlich/'.rr- ditic condition. Likewise, only history can explain why the genome is full of "fossil" genes: rrrriirrr'lir'lr explain 'I _ 5 -' zrr ill rir','rZtr.tan.l pseudogenes that have lost their function. Only the contingencies of history can cktotherur, u,echseln,alm the arbitrary nature of some adaptations. For instance, whereas ectothermic ("cold- Aortenbiigt-n / Enc'lothelme,Gleich- blooded") tetrapods have two aortic arches, "warm-blooded" endotherms have only one. \\'.1rme This difference is probably adaptive, but can anything except historical chance explain why birds have retained the right arch and mammals the left? Becausecharacteristics evolve from pre-existing features, often undergoing changes in functiory many feafures are poorly engineered, as anyone who has suffered lower back pentacl.rktvleliiinffingriee) Extre.mi- pain or wisdom teeth can testify. Or-rcethe pentadactyl limb became developmentally tät car-ralized,tetrapods could not evolve more than five digits even if they would be useful: the extra " finger" of the giant panda's hand is not a true digit at all, and lacks the flexi- gelenkig biiity of true fingers because it is not plqlggi (see Figure 21.8). Similarly, animals would certainly be better off if they could synthesize their own food, and corals do so by har- endosymbionlisch / I'}hotosynthese boring endosymbiotic algae-but no animal is capable of photosynthesis. If a designer were to equip species with a way to survive environmental change, it might make sense to devise a Lamarckian mechanism, whereby genetic changes wouid zr:fällig occur in response to need. Instead, adaptation is based on a combination of a random process (mutation) that cannot be trusted to produce the needed variation (and often does Inbegriff not) and a process that is the very epitome of waste and seeming cruelty (natural selec- tion, which requires that great numbers of organisms fail to survive or reproduce). It Siclrelzellanämie would be hard to imagine a crueler instance of nafural seiection than sickle-ceil anemia, auf Kosten whereby part of the human population is protected against malaria at the expenqgof hun- homozVgot dreds of thousands of other people, who are condemned to die because they are homo- heterozvroter Träger zygous for a gene that happens to be worse for the malarial parasite than for heterozY- gous carriers (see Chapter 12). Indeed, Darwin's theory of the cause of evolution was in Ern ägur.rgzu ziehen widely rejected just because people found it so distasteful, even horrifying, to cgntem- erhalten plate. And, of course, this process often does not preserve species in the face of change: ilore than 99 percent of ali species that have lirr"d *u äxtinct. Were they the prod- "n". ucts of an incompetent designer? Or one that couldn't foresee that species would have to Umstände adapt to changing circumstances? - t EVOTUTIONARYSCIENCE, CREATIONISN/, AND SOCIETY 531 'i' Many species become exti4c;! because of gql4petition, p.$de!iq4, and parasitism. Some :iorben.rrrs / Konkrrrrt'rrzi I']r,iLl,r- of these interactions are so appalling that Darwin was led to write, "What a book a dev- Iir'rt o srltr.t'cklir'lt ils' chaplain might write on the clumsy, wasteful, blundering, low, and horribly cruel KapL.rr/ ungtschickt works of Nature!" Darwin knew of maggql9 that work their way up the !4q41-123$gges \{at1en / Naseng.ingc into the brains of sheep, and wasp larvae that, having consumed the internal organs of a living caterpillat burst out like the monsters in the movie Ällen. The life histories of par- R.rupr'nI I ebcrrszvklen asites, whether parasitic wasp or human immunodeficiency virus, ill fit our concept of an lmnrrrncletizicnz intelligent, kindly designe(, but are easily explained by natural selection (see Chapter 18). No one has yet demonstrated a characteristic of any species that serves only to benefit a different speciet or only to enhance the so-called balance of nature-for, as Darwin saw, Cleichgerrichi r'ler'\.rlLrr "such could not have been produced through natural selection." Becausenatural selec- tion consists only of differential reproductive success,it results in "sel{ish" genes and u nierschieclIich!.I Fortpfl.rn1u ns:(,r- genotypes, some of which have results that are inexplicable by intelligent design (see iolg i ,,egoistischc"Cltnt' Chapter 14). We have seen that genomes are brimming with sequencessuch as transpos- vrrlluepacktnrii able elements that increase their own numbers without benefiting the organism. We have seen maternally tuansmitted cytople!r4!!€e4e! that cause male sterilitY in many plants, m ritteriichiibertragt'rro Cvtoprl;5p1.1 and nuclear genes that have evolved to override them and restore male fertility. Such con- tene / L-in|ruchtl-arkeitrlrr iVlarrn- flicts among genes in a genome are widespread. Are they predicted by intelligent design t--hen. Frnchib,rrkeiitlcl N1.irrnclrcrr theory? Likewise, no theory of design can predict or explain features that we ascribe to sexual selection, such as males that remove the sperm of other males from the female's seruelleSclektion / Sl.crr-ni,:n replodgqlivell4!!, or chemicals that enhance a male's reprodlrctive sllccess but shorten FortpflanzungsfrakL his mate's life spen. Nor can we rationalize why a beneficent designer would shape the l-el'enssp.rnnt: clcr Gt'schlechtsf..r lt- many other selfish behaviors that natural selectionexplains, such as cannibalism, sibli- nerin . Ceschu isterLa)tung.Siblizirl cide, and inJanticide. Kirrtlestiitun!1, i rrf.rn iiz icl

Evolution and its mechanisms, observed Anyone can observe erosiory and geologists can measure the movement of continental Elosir)r1,.\[rtrJgu r]g plates, which travel at up to 10 centimeters per year. No geologist doubts that these mech- anisms, even if they accomplish only slight changes on the scale of human generations, have shaped the Grand Canyon and have separated South America from Africa over the course of millions of years. Likewise, biologists do not expect to see anything like the ori- gin of mammals played out on a human time scale,but they have documented the mech- anisms that will yield such grand changes, given enough time. Evolution requires genetic variation, which originates by mutation. From decadesof genetic study of initially homozygous laboratory populations, we know that mutations arise that have effects, ranging from very slight to drastic, on all kinds of phenotypic char- acters (seeChapter B).These mutations can provide new variation in quantitative char- tlu.rntit.rii r c' \ [t'rknrale acters, seemingly without limit. This variation has been used for millennia to develop strains of domesticated plants and animals that differ in morphology more than whole (l.ricr')Sirrten, fiassen ,/ d.rnrestiziert families of natr-rralorganisms do. In experimental studies of laboratory populations of mi- croorganisms,we have seen new advantageous mutations arise and enable rapid adap- tation to temperature changes, toxins, or other environmental stresses.Laboratory stud- Cillstotte I Unrrrcltbcl.rstrrrrr:t'n ies have documented the occurrence of the same kinds of mutations, at the molecular level, that are found in natural populations and distingr"rish species. These mutations in- clude base pair substitutions, gene duplications, chromosome rearrangements, and trans- B.rscrtpaararrsL,ruscltr/ Ncrrtrtrl' position of transposable elements. No geneticist or molecular biologist doubts that the nLrnq \'(r11Chrtlttosorttctt differences among species in their genes and genomes originated by natural mutational processesthat by and large, are well understood. We know also that most natural populations carry a great deal of genetic variation that can yield rapid responsesto artificial or natural selection(see Chapters 9,7I, and 12).We krlnsLlich have seen allele frequency differences among recently established populations that can Aliol ileqr.renz..\llol häuiigkci t be confidently attributed to genetic drift (seeChapter 10). Evolutionary biologists have documented 1itera11yhr,rndreds of examples of natural selection acting on genetic and phe- notypic variation (see Chapters 12 and 13). They have described hundreds of casesin which populations have responded to directional selection and have adapted to new en- st-richtetcSelektion

g t.- 532 CHAPTER22

Ilesisttrrz gegenril.c.rhrsektiziden / vironmental factors, ranging from the evolution of resistance to insecticides, herbicides. Hertrizi cle,Unkrautlerniclrtungs- and antibiotics to the evolution of different diets (see Chapter 13). rlittel o Antibiotika Speciation generally takes a very long time, but some processes of speciation can also reproduktive Isolatiorr be observed. Substantial reproductive isolation has evolved in laboratory populations, R'lvi.loi.lie / Hvl.r'idicierrrnq.\'el and species of plants that apparently originated by polluploidy and by hybridization have bastarcliertrng . Kreuzultg been "re-created" de novo by crossing their suspected parent forms and selecting for the species' diagnostic characters (see Chapter 16). hr summary, the major causesof evolution are knowry and they have been extensively '''A rr: -----'_-' uerrpqe documented. The two major aspects of long-term evolutiorL anagenesis (changes of chai- K)adogenese acters within lineages) and cladogenesis (origin of two or more lineages from common ancestors)/ are abündantly supported by evidence from every possible source, ranging from molecular biology to paleontology. Over the past century, we have certainly learned of evolutionary processesthat were formerly unknown; we now know for example, that some speciesmay arise from hybridizatiory and that some DNA sequencesare mobile and can cause mutations in other genes. But no scientific observations have ever cast serious doubt on the reality of the basic mechanisms of evolution, such as natural seleclion" nor Abn'andltrng on the reality of the basic historical patternt such as transformation of characters and the origin of all known forms of life from common ancestors. Contrast this mountain of evi- dence with the evidence for supernatural creation or intelligent design: thereis no suchea- idencewhateuer.

Refuting Creation i st Argu me nts

Creationists attribute the existence of diverse organisms and their characteristics to mir- acles: direct supernatural intervention. As we have seen, it is impossible to predict mir- acles or to do experiments on supernatural processes, so creationists do not do original research in support of their theory.* Thus "creafion science," rather than providing pos- itive evidence of creatiory consists entirely of attempts to demonstrate the falsehood or UnzuJärrgliclrkeit/ irr Entrarrgelturg inadequacy of evolutionary science and to show that biological phenomena must, by de- anderer l\4öglichkeiterr fault, be the products of intelligent design. Here are some of the most commonly en- kurz countered creationist arguments, together with capsule counterarguments.

1. Evolution is outside the realm of sciencebecause it cannot be observed. Evolutionary changes have indeed been observed, as we saw earlier in this chapter. In any case,most of science depends not on direct observation, but on testing hy- potheses against the predictions they make about what we should observe. Obser- Daseinsfolmer vation of the postulated processesor entities is not required in science.

2. Evolution cannot be proved. Nothing in science is ever absolutely proved. "Facts" are hypotheses in which we can have very high confidence becauseof massive evidence in their favor and the absence rt,idersplücl-rIiclr of contradictory evidence. Abundant evidence from every area of biology and pale- ontology supports evolutiory and there exists no contradictory evidence.

3. Evolution is not a scientific hypothesis becauseit is not testable: no possible observa- rr idcrlegerr tions could refute it. Many conceivable observations could refute or cast serious doubt on evolutiory such urrbestreitlrar'/ Lrräkaml.risch,aus as finding incontrovertibly mammalian fossils in incontrovertibly Precambrian rocks. delr Präkanrbrium . Eigenheit / In contrast, any puzzling quirk of nature could be attributed to the inscrutabie will unergrürrdlicl.r and infinite power of a supernatural intelligencg so creationism is untestable.

"About the only quasi-exception to this statement was thet claim to have found commingled lternrischtl human and dinosaur footprints in fossilized sediments in a riverbed in Texas, supposedly showing that - . these organisms were contemporaneous IZeitut'rro>:cnl. Even if this claim had pioved tobe true, it would not have falsified evolution; but in any case, most creationists now acknowledge that the "humm" prilts _ are a mixture of fraudulent carvings {betriigcrische \4eißclarlreitenl and natural depressions [\ fr tiuitrngenJ.

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