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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 The University of ChicagoPress,Ltd., Lon-don DEDICATED IN APPRECIATION TO Virginia and Glenn D. Bouseman @ 1973by David L. HuIl All rights resewed. Published l97B University of ChicagoPressedition 1983 Printed in the United Statesof America 90 89 88 87 86 Iris and Robert H. Reid 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. 83-4855 575.0r'62 QH365.08H84 1983 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.Katherine 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. Contents D.L.H. I Introductory 3 16 37 Chapter I.. Introduction . Chapter II. The Inductive Method Chapter III. Occult Qualities Chapter IV. Teleology JJ Chapter V. Essences ot II eviews JosephDaltonHooker(1817-1911) WilliamBenjaminCarpenter( 1813-1885) H. G. Bronn( 1800-1862) ThomasVemonWollaston( I 821-1Bi8 ) FrangoisJulesPictet (1809-1872) AdamSedgwick( 1785-1873 ) RichardOwen ( 1804-1892) SamuelHaughton( 1821-1897 ) WilliamHopkins( 1793-1866) HenryFawcett( 1833-1884) FrederickWollastonHutton ( I 836-1905) FleemingJenkin ( 1833-1885) ol UT 87 118 126 L+2 155 1 1 1L LI 216 229 zto 292 302 Contents St. GeorgeJacksonMivart ( 1827_1900 ) and ChauncyWright ( 1830_t 875 ) Karl Ernstvon Baer (l7g}_l}7 6) Louis Agassiz( 1807-1873 ) Conclusion Bibliography Index J3 l itlo 428 450 +59 +69 trntroductory Introduction This leads me to remark that I have always been treated honestly by my reviewers, passing over those without scientific knowleirge as not worthy of notice. My views have often been grossly misrepresented, bitterly opposed and ridiculed, but this has been generally done, as I believe, i'gooä faith.Charies Darwin, Autobiography, p. l2S. Darwin expected theologians, people untrained in scientific investigation, and even those scientists who were strongly religious to object violently to his theory of evolution. He had also anticipated the skepticism of even the most dispassionate scientists. He had not Iabored over twenty years for nothing gathering facts to support his theory and attempting to discount those that apparently conflicted with it. But he had not anticipated the I have got fairly sick of hostile reviews. Nevertheless, they have been of use in showing me when to expatiate a little and to introduce a few new discussions. vehemence with which even the most respected scientists and philosophers in his day would denounce his efforts as not being properly "scientific." To the extent that these latter reactions were genuine and not the result I entirely agree with you, that the difficulties on my notions are terrific, yet having seen what arl the Reviews have said against me, r have far more confidence in the generar truth of the doctrine than r formerly had.-charres Darwin to T. H. Huxley, Down, December 2, 1860, Lit'e and. Letters,2:147. of religious bigotry, they can be explained by reference to the philosophies oT science popular in Darwin's day. In this chapter Darwin's understanding of the philosophies of science of his day and his own. views on science will be set out as fully as possible. Darwin had both the good fortune and the misfortune to begin his scientific 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 revolution, they were presented with the added advantage and obligation of recoriciling 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 differencebetweenepistemologyand 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. Introduction Darwin and His Critics Commencing with John Herschel's Preliminary Discourse on tha Study of Natural Philosoplty (1830), English-speaking scientistsbecame self-conscious about the proper method of doing science. During the years 1837-1842, when Darwin was residing in London and rvorking on the species problem, the great debate on the philosophy of science erupted between William Whewell (1794*1866) and John Stuart Mill (1806-1873). In 1833 Whewell contributed his Astronomy and General Physics Considered witlt reference to Natural Theology to the Bridgewater Treatises. In 1837 he published his History of the Inductiue Sciencesand in 1840 The Philosophy of Inductiue Sciences,Founded upon their History. Darwin was impressed by the breadth of l<nowledgeexhibited in these five volumes and remembered Whewell as one of the best converserson srave subiects to whorn he had ever listened.2 In 1843 Mill brought out his influential System of Logic, Ratiocinatiue and Inductiue, Being a Connected Vieut of the Principles of Euidence, and the Methods of Scientific Inuestigation. Although Mill had gathered most of what he knew of science lrom reading Whewell's volumes, his System of Logic was largely an empiricist attack on Whewell's reworking of Kant's rationalist philosophy. The key word in this dispute and in the methodological objections raised to Darwin's theory was "induction." It would be nice to be able to set out at this point the meaning which the disputants attached to this word, but I cannot. Everyone meant sornething different by it, and in the .works of a single man, one is likely to find many different uses of the word. Initially it was used by Francis Bacon (1561-1626) to contrast his abortive "inductive method" with the Aristotelian "deductive method." As popularly misconceived, the deductive method consistedin an irresponsible leap to a conclusion of high generality and the subsequentdeduction of consequencesof these generalizations regardless of observedfacts. Perhaps the scholasticsat their worst were guilty of such maneuvers, but the above characterization was not only a parody of Aristotle but also fails to identify the actual weaknessesin Aristotle's system. The inductive method, also as popularly misconceived, began with observation and proceeded by the cautious construction of generalizations of greater and greater generality. The deductive method proceeded from the peak of the pyramid of knowledge down to its base, whereas the inductive method started at the base and worked up. The superiority of a pyramid resting on its baserather than its peak was obvious. Although Bacon carne close to advocating the inductive method as set 2 . D a r w i n ( 1 9 5 8 ) ,p . 6 6 . out above, Flerschel, Whewell, and Mill were all alvare of its shortcomings. Science had not and could not proceed by the method set out by Bacon. Yet Bacon was the patron saint of the scientific revolution, and "inductive" was an honorific title not to be discarded' lightly' Al1 three men wanted to reservethe term "induction" for the processby which scientific knowledge. is attained. Simultaneously they also wanted to use it to refer to the means by which such knowledge was proved {actual. For Herschel and Mill induction was the discovery of empirical laws in the facts, reasoning from the known to the unknown. Concurrently, this inductive method insured the truth of these laws. For Whewell, induction was the superinducing of conto cepts o11the facts by the mind. Experience might stimulate the mind form a concept, but once the appropriate concept had been conceived, truth was guaranteed. For Herschel and Mill, both Kepler's laws and the parallel line postulate of Euclidean geometry were inductions from experience; for whewell they were self-evident truths whose truth could be known a priori. Induc' Whe*eli did pot reply to Mill for six years, then published his Ol tion,wit'hEspecialReferencetoMr.'!.StuartMill'sSystemofLogic (1849), just in time for the third eclition of Mill's System of Logic''Ihe because controversy which ensued was gradually decided in Mill's favor, nct because but Whewell, of that to superior especialiy was position Mill's emwhewell,s version of I(antian philosophy ran contrary to the rising scientific over this controversy of midst the in It was tirne. the piricism of method that Darwin published his On the Origin of Species by Means ol Natural selection, or tlte Preseruation of Fauoured Races in the struggle coincidence was' to say the least, a for Life (1859). For Darwin, this mixed blessing. which, In his last year at cambridge, Darwin read I{erschel',sDiscourse burnhim"a in stirred (1818), Narratiue Personal along with I{umboldt,s structure noble the to contribution humble most ing zeal to add even the this of Natural Science."3 Herschel had written his book to eticit precisely revolution. scientific the about had brought reaction in his readers. Newton of Newton's Henceforth, all scientists had to do was to filI in the details the Newwithin always but it, great structure, perhaps expanding upon reiigion' and science between tonian framework. Nor was there any conflict scientists but the Bible, o{ Geology had challenged the literal interpretation themselves and theologians had made their peace. scientists could concern the first crebut with the workings of the material world, once created, 3 . D a r w i n ( 1 9 5 8 ) ,p . 6 7 . Darwin and His Critics Introduction ation, 'life, mind and soul were the province of the theologian. "To ascend to the origin of things, and to speculate on the creation, is not the businessof the natural philosopher."a Not only were scientistsmaliing but he was not prepared for the criticism which his methodology was to receive from the most respected philosophers and scientistsof his day. Most contemporary commentators tend to dismiss these criticisms as facile, disingenuous and superficial, suspectingthat they stemmed more from a distaste of the content of Darwin's theory than from his methodology, but this dismissal is itself too facile. Certainly the repeated invocation of the great contributions to the noble edifice of science and to mankind by applications of science in medicine and industry, but their discoveriesalso lent support to religion through natural theology. As they discovered more clearly how nature worked, they showed how great the creator's wisdom had been. In his youth Darwin had hoped to join in this great parade of scientists and men of God marching arm in arm to produce a better world. Instead he stopped it dead in its tracks. In his early publications, Darwin gave every appearance of contributing his share to received science. His journals concerning the voyage of the Beagle were in the best tradition of such narratives. FIis monographs on living and fossil barnacles certainly were in no way controversial. Even the publication of his papers on the formation of the Parallel Roads of Glen Roy (1839) and of coral reefs (1842), though theoretical in nature, 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 the sides of a glen in Scotland in terms of the gradual elevation of the land. The parallei roads were actually the remnants of former beaches. In the second, he explained the forrnation of coral reefs in terms of the gradual subsidence of the ocean floor. New coral grew on the old as it feii beneath the surface of the warer. But with the publication of the Origin oI Species,large segments of the scientific and intellectual community, turned on him. Both Adam Sedgwick, the eminent geologist, and Richard Owen, the leading comparative anatomist of the day, had encouraged Darwin in his early work. After the Origin, their praise turned to ridicule. Sedgwick (1860) complained that Darwin had "departed from the true inductive track." Owen, while admitting that he himself had casually entertained the notion of natural selection,had judiciously refrained from enunciating it. It was "just one of those obvious possibilities that might float through the imagination of any speculative naturalist; only the sober searcher after truth would prefer a blamelesssilence to sending the proposition forth as explanatory of the origin of species, without its inductive foundations."s Darwin was prepared for the abuse which the content of his theory, especially its implications for man, was to receive from certain quarters, 4. Herschel(1830),p. 38. 5. Owen (1860). Baconian method by many of Darwin's critics and even by Darwin himself indicated no great understanding of the actual nature of this method or the philosophy from which it stemmed, but the leading philosophers contemporary with Darwin, John Herschel, William Whewell, and John Stuart Miil, were equally adamant in their conviction that the Origin of Species was just one mass of conjecture. Darwin had proved nothing! From a philosophical point of view, evolutionary theory was sorely deficient. Even today, both Darwin's original efforts .and more recent reformulations are repeatedly found philosophically objectionable.GEvolutionary theory seems capable of offending almost everyone. In the nineteenth centur-y, "to be scientific" meant to be like John I-Ierschel'sextension of physical astronomy to the sidereal legions.T Thus, Darwin was especially anxious to heal the opinion of Herschel, the "great philosopher" referred to in the opening paragraph ol the Origin He sent Herschel a copy of his bool< and wrote to Lyell to pass on any comments which the great physicist might make since "I should excessivelylike to hear whether I produce any effect on.such a mind."8 Herschel's opinion was rapidly forthcoming. Darwin wrote to Lyell, "I have heard, by a roundabout channel, that Herschel saysmy book 'is the law of higgeldy-piggeldy.' What this exactly means I do not know, but it is evidently very contemptuous. If true this is a great blow and discouragement."e In the face of such a rejection by the most eminent philosopher-scientist of the century, it is easy to understand Darwin's pleasure when he discovered in an equally roundabout way that another great philosopher, John Stuart Mill, thought that his reasoning ln the Origin was "in the most exact accordance with the strict principles of logic."lo On closer examination, however, Mil.l's 6. See,for example,Woodger(1929), Kneale (1949), von Bertalantry(1952), Grene (1958), Himmelfarb(1959), Manser (1965), and Mooreheadand Kaplan (1e67). 7 . C a n n o n( 1 9 6 1 ) ,p . 2 3 8 . 8. Darwin,November 23, 1859,Lif e andLetters(1887),2:26. 9. Darwin,December 12, 1859,ibid., 2:37. 10. Darwin,HenryFawcettto C. Darwin,January16, 1861,More Letters(1903), 1:189. Dalwin and His Critics endorsement can be seen to be not nearly reassuring. Darwin had prop_ erly used the Method of Hypothesis, but this rnethod belonged to the logic of discovery, not proof. In spite of twenty years' labor, Darwin hacl failed to provide proof for his theory of evolution by natural selection. Darwin's own views on the nature of science exhibited the conflicts and inconsistenciestypical of his day. He evidencecl the usual distrust of ,,hypotheses" while grudgingly admitting their necessity. For example, in a letter to I{ooker, Darwin claimed that he looked upon "a strong tendency to generalize as an entire evil"11 and yet admitted in his Autobiography: "f cannot resist fo'ning one on every subject.,'l2 In the opening paragraph of the Origin of SpeciesDarwin sketched the following history of the development of his theory: When on board H.M.S. "Beagle," as naturalist, I was much struck with certain facts in the distribution of the inhabitants of south America, and_in the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some lieht on the origin of species-that mystery of mysteries, as it has been called by one of our greatest philosophers. On my return home, it occurred to me, in 1837, that something might perhaps be made out on this ques_ 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 myself to speculate on the subject, and drew up some short notes; these I enlarged in lB44 into a sketch of the concluiions, which then seemecl to me probable: from that period to the present day I have steadily pursuedthe sameobject (p. 1). rn his Autobiography Darwin recalls roughly this same sequenceof events but adds that he "worked on true Baconian principles and without a'y theory collected facts on a wholesale scale."t3 But Darwin was well aware that the possibility of speciesevolving had occurred to him soon after his return from his voyage on the Beagte (if not before) and his principle of natural selection not much later, in october 1838. Five years may have elapsed before he permitted himself to write an essayon the subject, but he had speculated and collected facts in the iight of these speculations from the very first. The source of this fabricatio' is easy to uncover. one of the most prevalent confusions in the work of even the best scientists and philosophers was between the temporal order of an actual scientific investigation and 1l. Darwin, January11, 1844,More Letters( 1903) , 1: 39. 1 2 . D a r w i n ( 1 9 5 8 ) ,p . 1 a l . 1 3 . D a m i n ( 1 9 5 S ) ,p . 1 1 9 . Introduction the logical order of a reconstruction of scientific method. According to empiricist epistemology,all knowledge has its foundation in experience. This tenet was mistakenly taken to imply that a1l scientific investigation has to begin with observation. The true inductive scientist began collecting data indiscriminately, with no preconceived ideas, and gradually evolved broader and broader generalizations.The process of scientific investigation assured both the truth and the empirical meaningfulness of the resultant propositions. Deductivists approached nature with a hypothesis already in mind, and speculators flew too quickly to generalizations of too great a scope. Thus, Darwin can be found saying of his coral reef paper, 'oNo other worl< of mine was begun in so deductive a spirit as this; for the 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 evolution, he conceded to Asa Gray, "What you hint at generally is very, very true: that my work will be grieiriously hypothetical, and large parts by no means worthy of being called induction, my commonest error being probably induction from too few facts."15 In a letter to FIenry Fawcett, however, Darwin indicated that he realized that data cannot be gathered efficiently without some hypothesis in mind: About thirty years ago there was much talk that geologistsought only observe and not to theorize; and I well remember someone saying that at this rate a man might as well go into a gravel-pit and count the pebbles and describe the colours. FIow odd it is that anyone should not see that all observation must be for or aeainst some view if it is to be of any service!t6 "to What mattered was that the hypothesis be an empirical hypothesis, one that could be verified or refuted by observation, and that serious attemPts be made to gather the relevant data. Immediately after saying that his coral reef paper was begun in a deductive manner, Darwin adds, "I had therefore only to verify and extend my views by a careful examination of coral reefs."l7 Darwin's own experience as a scientist forced him to recognize that the order in which hypotheseswere formed and the relevant data gathered was not rigidly set. It helped to have a hypothesis in mind, but hypotheses had to be changed as the investigation proceeded.ls His theory of the formation of coral reefs was formulated before he had collected 14. Ibid.,p. 98. 1 5 . D a r w i n ,N o v e m b e2r 9 , 1 8 5 9M , o r e L e t t e r s( 1 9 0 3 ) ,1 : 1 2 6 . 18, 1861,ibid., l:195. 16. Darwin,September 1 7 . D a r w i n ( 1 9 5 8 ) ,p . 9 8 . i B . I b i d . ,p . 1 4 i . t0 Dalwin and His Critics very much of the relevant data and turned out to be largely factual. I{is theory of evolution by natural selection was formulated after several years of observationsas a naturalist, followed by two decadesof additional, selective investigation, and it too was basically correct. I{is theory of the Parallel Roads of Glen Roy had much the same history on a smailer scale as his theory of evolution, but was mistaken. In the case of inheritance, Darwin actually did amass facts wholesale before he succeeded in working out his theory of pangenesis. Its {ate was even more unhappy than that of the Parallel Roads theory. Clearly there was no connection between the Introduction 1l chided him for objecting to the skepticism of scientific men. "You would not fulminate quite so much if you had had so many wild-goose chases after facts stated by men not trained in scientific accuracy."2o Darwin's conservative views on publication were rewarded to some degree. His Origin ot' Species did not suffer the same fate as those works on evolution that had preceded it. It was treatecl as a serious work of science even by those who denounced it. But a similar reticence on the part of Gregor Mendel resulted in his laws of heredity being overlooked 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 hypothesis. appearance of the Origin He too wanted to avoid being branded a speculator. In his original paper he barely alludes to his unobservable "factors," Ilowever, Darwin did think that the temporal order of the verification and the publishing of a hypothesiswas important in the sociology of science, though the cogency of his entire argument rested upon their existence. In a letter to Carl Nägeli (X{endel, 1867), he claimed that, "as an empirical lvorker" he had to "define constancy of type as the retention of a character during the period of observation." Pärhaps Darwin's advice might protect both for the sal<eof the scientist's own reputation and for the, sake of the acceptanceof his theory by the scientific community. To a young scientist, Darwin advised, "I would suggest to you the advantage, at present, of being very sparing in introducing theory in your papers (I formerly erred much in Geology in that way) ; Iet theory guide your obseruations, brt scientists from being engulfed in half-baked scientific publications, but it also contributed to the obscurity of Mendel's potentially great contribution to science. Because l-amarck neglected the niceties oJ the sociology of sci- till your reputation is well established, be sparing of publishing theory. It makespersonsdoubt your observations.'l1e ence, his worl< was ignored with disdainful embarrassment.Because Mendel was too scrupulous in observing them, his work was overlooked. Darwin Darwin also had a reason for advising restraint in publication which was less personal and more significant to the progress of science. I{e was aware of the fate of Lamarck and Chambers. Chambers had. received con- strucl<an appropriate compromise. Darwin's beliefs on the ethics of pubiication go a great way toward explaining his reticence in publishing his own views on the origin of species until his big book was complete. Darwin emphasized the importance of providing empirical evidence for scientific hypothesesfor still another rea- siderable popular acclaim but scathing denunciation from the academic community, including T. H. Huxley (1854). Lamarck received norhing but ridicule lrom all sides. Dar-win criticized Larrar-ck and Chambers, nor for suggestingmechanisms for evolution which he thought were mistaken, but for foisting their views on the scientific community without sufficient effort at careful formulation and verification. Lamarck and chambers looked upon the process of scierrtific verification as a very casual affair. Darwin looked upon these matters as of utmost g.avity. Lamarck published radically new theories in a variety of fields as diverse as mineralogy and meteorology.He felt that the originality of his impressionisticsketcheswould be enough to rnotivate others to undertake the subordinate task of filling out and verifying his theories. As Burkhardt (1970) has aptly observed, public neglect and private ridicule were the late of his theories. prior ro knowing that chambers was the author of the vestiges of creation, Darwin 19. Darwin, 1863,More Letters(1g03),2:323. son. The science of Darwin's day was filled with metaphysical principles enunciated as if they were scientific laws. Darwin found Flerbert Spencer to be one of the chief offenders in this regard. Because of the jargon of the period, Darwin's discussionsof the differences between scientific laws, the axioms of mathematics, and metaphysical principles are ltone too clear, but in these matters he was no worse than the leading empiricist phiiosophers of the day. He tended to distinguish the forrnal from the empirical sciencesby the prevalence of deductive reasoning in the for"mer. Of Spencer, Darwin complained: His deductive manner of treating any subject is wholly opposed to my frame of mind. I{is conclusions never convince me; and over and over again I have said to myself, after reading one of his discussions,20. Darwin,April 30, 1861,More Letters(1903),2:443;seealso,Darwin (1871), p. 606. 12 Darwin and His Critics "Here would be a fine subject for half-a-dozen years' work." Ilis fundamentai generalizations (which have been compared in importance by some personswith Newton's Laws ! ) which I daresaymay be very valuable under a philosophical point of view, are of such a nature that they do not seem to me to be of any strictly scientific use. They partal<e more of the nature of definitions than of laws of nature. They do not aid me in predicting what will happen in any particular case. Anyhow they have not been of any use to me.21 The distinction w}rich Darwin discerned in the works of Spencer was between a scientific hypothesiswhich has not yet been verified and a purely metaphysical principle which, by the methods of science, cannot be confronted by empirical data at all. FIe felt "inclined to cavil at speculation when the direct and immediate effect of a cause in question cannot be shown."2: Darwin doubted the merits of Spencer's scientific work, not merely because the evidential basis was frequently lacking but because Darwin doubted that there was any. Although Darwin envied mathematicians their "sixth sense,"he also mistrusted them. For example, in the sixth edition of. the Origin, he had to change the number of descendantsof a single pair of elephants which would still be alive after 750 years from 15 million to 19 million. "I got some mathematician to make the calculation. and he blundered and caused me much shame."2sAgain to Hool<er, he remarked, "You will be amused to observe that geologistshave all been misled by Playfair, who was misled by two of the greatest mathematicians! And there äre other such cases; so we could turn round and show your reviewer how cautious geologists ought to be trusting mathematicians."2a Darwin could not help but know the crucial role which mathematics had played in physics, since Hersihel had repeatedly emphasized it in his Discourse,.but it did not seem to be in the least useful in his own work in biology. On occasion he had to make some simple computations. When these proved too much for l.rim, he asked for help. In later life his son 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, mathematics consisted of deductive reasouing, and he distrusted greatly "deductive reasoning in the mixed sciences." In his own work, 21. Darwin (1958), p. 109; seealsoletter to J. Fiske,December8, 1874,Life a n d L e t t e r s( 1 8 8 7 ) , 2 : 3 7 1 . 22. Darwin,March4, 1850,More Letters(1903),2:133. 23. Darwin,April 15, 1872,ibid.,1:336. 24. J)arwin,August7, 1869,More Letters(1903),l:315. Intloduction IJ he seldom was presented with a situation in which he could use such deductive reasoning. He .was constantly forced to deal in probabilities, and no one could tell him how to compute and combine such probabilities. I{e agreed with Lyel1 about "mathematicians not being better able to judge of probabiiities than other men of common-sense."?sDarwin tended to _. extend his view of mathematicians to ph;,sicists,especially in their attempts to calculate tl-reage of the earth. They had been wrong in their geological calculations so many times in the past, Darwin was not overly terrified by the specter of Lord Iielvin's estimation of the age of the earth.26 One reason which Darwin frequently gave for the Origin's being so maligned and misunderstood was that Wallace's joirrt discovery had forced him into premature publication. No similar pressure forced Darwin to publish his theory of pangenesis,and it met with even more resistance than lhe Origin had. In reality, all of Darwin's theoretical work had much the same structure. As Darwin put it: "The line of argument often pursued throughout my theory is to establish a point as a probability by induction and to apply it as hypotheses to other parts and see whether it will solve them."2? If it did solve them, then Darwin thought- that there was good reason to accept the hypotheses tentatively. As Darwin wrote of F. W. I{utton's review of the Origin: He is one of the very few who see that the change of species cannot be directly proved, and that the doctrine must sink or swim according as.it groups and explains phenomena. It is really curious how few judge it in this way, which is clearly the right way.28 And in his autobiography he saysof his theory of par.rgenesis: Towards the end of the work I give my well-abused hypothesis of pangenesis.An unverified hypothesis is of little or no value. But if anyone should hereafter be led to make observations by which some such hypothesis could be established,I shall have done good service, as an astonishing number of isolated facts can thus be connected together and rendered intelligible.20 Darwin produced several theoretical works in his career: two were in error (pangenesisand his explanation of the Parallel Roads of Glen Roy) 25. Dar-win,June 17, 1860, ibid., 1:154. For severalamusinganecdotesabout Darwin's mathematical ineptness see Himmelfarb (1959). 26: For a further discussion see the comments to the reviews of Haughton and Fawcett. 27. DeBeer (1960), 3:142. 2 8 . D a r w i n , A p r i l 2 3 , | B G L ,L i f e a n d L e t t e r s ( 1 8 8 7) , 2 : 1 5 5 . 29. Darwin (1958), p. 120. 15 Darwin and I-Iis Clitics Intloduction and two correct (evolutionary theory and his explanation of the formation of coral reefs).30His procedures in formulating. articulating, and verifying these theories and explar-rationswere roughly the same, yet no one com- book that scientifrc revolutions are so traumatic that no reasons can be given for preferring one theory to another. Either one accepts the old theoly and its standards of rneaningfulness and truth or the new theory and its differing standards. The transition is almost mystical. Needless to say, considerable controversy has followed upon l{uhn's reconstruction of 14 plained of the methodology of l.risGlen Roy or coral reefs papers. If Darwin's methodology was faulty in the Origin, then it should have been equally faulty in all of his scientific works. What was wrong with Darwin's theories? Was his methodology faulty? What is the nature of inductive formulation and proof which eluded Darwin? These are the questions which occur to the modern reader when first confronted by the reviews of the Origin of Speciesand Darwin's later work, especially the Descent of Man. Some of the reviewers were obviously biased. Some were merely mouthing undigested platitudes. But many of the reviewers were competent scientistshonestly trying to evaluate a novel theory against tl-re commonly accepted standards o{ scientific excellence, and evolutionary theory consistently came up wanting. The solution to these puzzles can be found ir-r the philosophies of science promulgated by such philosophersas I{erschel, Whewell, and Mill and their most important predecessors,Aristotle, Bacon, and Newton. Darwin was caught in the rniddle of a great debate over some of the most fundamental issues in the philosophy of science-the difference between deduction and induction and the role of each in science, the difference between concept formation and the discovery of scientific laws, the lelation between the logic of discovery and the logic of justification, the nature of mathematical axioms and their relation to experience, the distinction between occult qualities and theoretical entities, and the role of God's direct intervention in nature. Before philosophers of science had thoroughly sorted out these issues,they were presented with an original and highly probiematic scientific theory to evaluate. That they rejected evolutionary theory, a theory which has outlasted many of the theories judged to be exemplars of scientific method, says something about the views of science held by these philosophers and scientists. In the succeedingchapters, the interconnections between Darwin's theory of evolution and the philosophiesof scienceculrent in his day will be traced. It is hoped that this discussion will aid the reader in understanding the various criticisms in the ensuing reviews and in placing them in their appropriate conceptual setting, I(uhn (1962) has argued in his influential 30. For a discussionof some of Darwin's other scientifictheoriessee Ghiselin (1969). scientific revolutions as fundamentally arational processes.llowever, all of' the discussions in this dispute have centered on revolutions in physical theory. The revolutions in biology have been al1 but ignored.3l The essays in this anthology should provide arnple source material for the disputants on the valious sidesof this controversy. In Chapter 2 the logic of justification ar.rd its relation to discovery will be examined. What did it take ro proue a scientific theory? Why had Newton's theory supposedly fulfilled the requirements of proof while Darwin's failed? In Chapter 3 the problems,surrounding concept formation and meaning will be discussed.Early scientists were deeply impressed bv the failure of Aristotelian science in the hands of the Scholastics. They identified this failure rvitl'r the "deductive method" and with the central role of "occult qualities" in ear'ly scientific theories. The fear of occult qualities was so strong in many scientiststhat any reference to unobservables was looked upon with extreme suspicion.But coexisting with this hard-nosed empiricism was an equally strong belief in God as an underlying first cause and his occasional dilect intervention in natural processes.This schizophrenic attitude of scientistsproved to be one of the strongest impediments to the acceptance of evolutionary theory. As I(uhn (1962) has observed: "For many men the abolition of that teleological kind of evolution was the most significant and least palatable of Darwin's suggestions.The Origin of Speciesrecognizedno goal set either by God or nature" (p. 171). Chapter 4 will deal with the effect that essentialismhad on the acceptance of evolutionary theory. Although this topic has been discussedextensively elsewhereseit is too intimately connected with the problems at issue to allow omission..Seldom in the history of ideas has a scientific theory conflicted so openly with a metaphysical principle as did evolutionary theory with the doctrine of the immutability of species.s3 3 1 . S e eR u s e( 1 9 7 0a n d 1 9 7 1 ) ,G r e e n e( 1 9 7 1 ) ,a n d G h i s e l i n( 1 9 7 1 ) . 3 2 . M a y r ( 1 9 5 9 a )a n d H u l l ( 1 9 6 5) . 33. The following works are recommended for further reading in the philosophies of Aristotle, ßacon, llerschel, Whewell and Mill : Blunt (1903), Ducasse (1951 and 1960), Anschutz (1953), Heathcote (1953), Hochberg (1953), Strong (1955), Cannon (1961), Walsh (i962), Grene (1963), and Butts (1968). fhe Inductive Method t7 with those of their principles. But this was not the natural history and experience that was wanted; far from it.t 2 ' The Inductive Method rn the light of the great advances in physics in the seventeenth and eighteenth centuries, nineteenth-century philosophers ancl scientistscollaborated to produce a philosophy of scienceconsistentwith these achievements. In their informal remarl<s these authors tended to provide useful insights into the scientific enterprise, but when they tried to be rigorous in their characterization of the scientific method, they tended to make pronouncements which frustrated the rational evaluation of ner.vlyemerging scientific theories, specifically evolutionary theory. In this chapter, the philosophies of scienceof Aristotle, Bacon, Herschel, whewell, and Mill will be sketched, both as these men set them out and as they r.verepopularly misconceived. It will be argued that evolutionary theory did fail to meet the standards of proof established by these philosophers for the simple reason that no theory could possibly fulfill them, including the prrysical theories which theseauthors had chosenas paradigm. In Darwin's day Aristotle was lool<ed upon by scientists as the author of infinite error and Bacon as the man who fashio'ed the method which Newton was to use to unlock the mysteriesof the universe. Bacon's characterization of ancient pl-rilosopherswas typical: From a few examples and particulars (with the addition of common notions and perhaps of some portion of tl-re received opinions which have been_most popular) they flerv at once to the most g".r".ul conclu_ sions,.or first principles of science. Taking the trutrr of tl-reseas fixed and they proceeded by means-of intermediate propositions .immovable, to educe and p.ove from them the inferior conclusions; and äut'of these they framed the art. After that, if any new particulars and examples rep.u.gnanjto their dogmas were mooted and adduced, either they sultly 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_ ticulars as were not repugnant they labored to issign causesin co.rformiry As far as Aristotle's professed epistemology is concerned, Bacon's characterization 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 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 to accomplish this end. Future philosophers of science like Bacon, Flerschel, and Mill will join Aristotle in his quest for absolute certainty but will attempt to obtain it by a strict application of inductive logic. Confusion over the nature of deQuction and induction is one of the most conspicuous features in attempts to set out a philosophy of science from Aristotle to John Stuart Mill. The metaphor that permeates the literature is that of a pyramid. For example, Adam Sedgwick (1860) complains of Darwin's theory: But I must in the first place observe that Darwin's theory is not induc-tiue,-rrot based on a series of acknowledged facts.pointing to a general conclusion,-not a proposition evolved out of facts, logically, and of course including them. To use an old figure, I look on the theory as a vast pyramid resting on its apex, and that apex a mathematical point. Deduction proceeded from the most general propositions at the apex of the pyramid to the particulars at the bottom, induction from particulars to generalizationsof broader and broader scope. A more misleading metaphor is hard to imagine. It is inapplicable to Aristotelian iogic. Both Whewell and Mill were well aware that it was inapplicable to logical inferences as they viewed thern. Yet the metaphor persisted, and has done so to this day in spite of the efforts of generations of iogic plofessors. The pyramid which people have in mind when they contrast deduction with induction is not a pyramid of inferences but a pyramid of concepts like the Linnaean hierarchy.' At the peak of such a pyramid is the ciass of greatest generality, e.g., animals. Animals are divided into additional classes of reduced scope, e.g., protozoans, round worms, and chordates. Each of these classesis subdivided in turn until the lowest level is reached-species, 1. Bacon(1620);bk. I- AphorismCXXV. 2. For example,seeJ. J. Bakerand G. Allen ( 1968). l9 Darwin ar-rd FIis Critics rlre Inductive Method subspecies,ol valieties. At the bottom of the pyramid are arrayed individual organisms. When we turn to a consideraiton of statements of greater and greater generality and inferences among thern, the whole idea of descending and ascending in a pyramid ceasesto be appropriate. For example, the following Hcrc lhe increase in generality is obvious. The conclusion is more general tbiLn the premises taken separately or together. But there has been no lscent in the pyramid of concepts. Crows and blackness are rnentioned in all the constituent statements. To use such an inductive argument one rnust alleady l<now how to recognize crows and the color black. .fhe rnrportant difference between deduction and induction which has 1B hypothetical syllogism is the classic example of an Aristotelian deductive arsument: (1) cmergecltlrrough the years turns out to concern not generality but certainty. In a valid deductive argument, the conclusion follows necessarily from the prernises.If the premisesare true and the argument valid, the conclusion rnusl be tlue. Both arguments (1) and (2) are deductive in this sense. All hairy quadr-upedsare animals. All hor"sesare hairy quadrupeds. I-Ience, all horses are animals. Although the inference in hairy the from the premises to quadmpeds, conclusion and hairy the conclusion. quadrupeds is no less general than Ilorses are included either are included in animals, of the premises. It but retains leference to the class of smallest scope (horses.) and largest scope (animals). Only the middle the individual, term In an inductive argument, the conclusion follows from the premises, if at all, rvith only a certain degree of probability. If the premises ere true anrl the argument warrantedr then the conclusion is probably true. fn an inductive argument there is always the possibility that true premises will is deductive, no dccrease in generality accompanies this argument has dropped out. Even no decrease in generality when accompanies the deduction is to the inference from the premises to thc conclusion: (2) All men are rnortals. Socratesis a manI{ence, Socrates is a mortal. Once again, the conclusion contains reference to the class of greatest generality. One has not descendedin any pyrarnid of inferences. The story is somewhat different for induction. The paradigrn exampie of an inductive inference is induction by simple enumeration. In such inferences, one reasons from a series of singular statements about individuals to a universal o c n e r a l i*^'"*-"^' zrfnn' ' ö.-_''' (3) This crow is black. f' ',i it, ir.i l't -ff, i... fi l:r I$ : lead to a false conclusion. For examirle, in argument (3) it turns out that not all crows are black (nor all ravens; nor are all swans white). It is casy to shorv that the difference between deductive and inductive aryuments does not depend on any putative decreaseor increase in generalitv betiveen premisesand .conclusions.For example, the following argument is analogousto the deductive argument (2), yet it is inductive. It is inductir.+ becausethe conclusion does not follow necessarilvfrom the nremises: (4) [:\: Almost all swans are white. The Brookfield Zoo owns three swans. 'h,i I{ence, they are probably white. $r' &,ir. $ll"i: ii" $i $:' N. Sirr $.,, s\ In the ensuing discussionof the philosophies of Aristotle, Bacon, Flerschel, Whnyell, and Mill, we will use "cleduction" and "induction" in the modern scnscof demonstrative and nondemonstrative inference. Our anachronistic usaqeproducesless distortion than one might think, sirrce ali the arguments This crow is black. $r n'hich these philosophers considered deductive are also deductive in this .$|.r', This crow is black. g:'i: This crow is black. ti' li' f-li'' li. ir J,, $,., i., $ystcrnsof logic now are included in one group or" the other. Even the difference .ir-rlat.ionale does not introduce any change in ernphasis, since one oI the chief concerns of philosophers from Aristotle to Mill was to ii evade lhe urrcertainty inherent in inductive inferences. Ilacon, Flerschel, f' .$ ., Hence, all crows are black. modern senseand all those that were thought inductive remain inductive. 'i'he difference betvveen the two usages stems from the rationale used to nräke the clistinction and from the fact that certain types of inferences rr'hich cr:unted as neither deductions nor inductions in some of the earlier |.l f, .f; l I 20 Darwin and FIis Critics rhe Inductive Method attempt to eliminate it by trying to make inductive inferences more rigorous, Aristotle by recourse to intuition, and whervell bv reference to self-evident truth. small induction,s but as Aristotle's own efforts and those of his followers give ample proof, these precautions tend to be ignored in an epistemology based on the infallible intuition of immutable essences.The source of error in Aristotle's epistemology is not the deductive organization of hnowledge. After all, verification by the deduction of observational consequencesis one of the best ways of checking the truth of a scientific law, but deduction to the individual as exemplified in argument (2) has no place in Aristotelian and Mill For Aristotle, k'owledge began with the observation of individuars rike Callias, Socrates,Alcibiades, and Ajax and proceeded by simple enumeration until one intuited that which is universal in .them-their essence,or formal cause. This process of concept formation preceded any inductive inferences in the strict sense,since it preceded the formation of statements. It cannot be represented as in argument (3), since in this argument one already has the concepts, crow and black. one merery observesindividuals and intuits their essence.For example, one might intuit that all the inclividuals listed above were men, or human beings, or animals. Intuition need not begin with the lowest universal and proceed only iater to universals of higher generality. It is possible to observe only one member of one speciesof a universal of high generality and still correctly intuit that universal. usually more extensive observations are necessary.The number and variety of observations needed for intuition vary from person to person and from subject mattel' to subject matter. Fewer observations are usually necessaryin mathematics than in such empirical sciencesas biology. Nor did Aristotle think that the preceding enumeration of individuals could be complete, since he believed that there were indefinitely rnany individuals in any species. It is not possible to observe all human beings and then merely by mechanically summing. their properties to discover their.essenceIntuition was necessary. Little has been said thus far about intuition. There is very little to say. Although intuition is the source of all certain knowledge, Aristotle hardly mentions it. According to Aristotle, the essenceof mankind is to nous, to know, to intuit. Man has the capacity for the direct apprehension of the essenceof things, to see the universal in the individual-and in this capacity intuition is infalliblels Aristotle gives no justification for the existence of infallible intuition. He merely observesthat without it, the acquisition of certain knowledge would be impossible. For Aristotle, scientific knowledge had to be universal, immutable and absolutely certain. The existence of essencesassured that it would be universal and imrnutable. Intuition guaranteed that it would be certain. Aristotle can be found saying that, whenever observation and theory co'flict, credit must go to obserwationaand warning against speculation from too 3. Aristotle,PosteriorAnalytics,pt. 2, ch. 19. 4. Aristotle, The Generation ol Animak,76Ob2B. 2l epistemology.Science deals only with that which is universal, with essences. After essenceshave been genuinely intuited, checking by observation is superfluous. By the time of Francis Bacon (1561-1626), the scientific revolution was well under way with the work of Copernicus, Galileo, Tycho Brahe, I(epler, Gilbert, and I{arvey, but to anyone living at the time the trend would have been difficult to discern. Bacon hoped to replace the Aristotelian deductive method with his method of i-rue induction, or induction by exclusion. Just as Aristotle had devised a set of lules for deduction, Bacon was going to do the same for inductive logic. I{e hoped to produce an inductive machine for grinding out true, scientific laws. Bacon's plan was to begin with extensive gathering of data without any speculation.GIfe felt that the best way to preclude any premature speculation was to have this labor performed by unlettered underlings. Besides, he believed that it was "somewhat beneath the dignity of an undertaking like mine that I should spend my orvn time in a matter which is open to almost every man's industry."? No doubt comments like these prompted Harvey to say that Bacon wrote philosophy "like a Lord Chancellor." Bacon was never to have his army of workers. Instead, in the last year of his life he himself tried to mal<e a beginning in the extensive gathering of data completely on his own. Even if Bacon had been given his army of workers, it is doubtful that his enterprise would have been very successful. It is now commonplace to recognize, as Darwin recognized over a century ago, that "the observer can generalize his own observations incomparably better than anyone else" and that "observation must be for or against a view if it is to be of any service." Bacon hoped to assure the truth of his generalizationsby extensive factgathering and induction. As data were gathered, they were to be entered on three tables-a table of essence,a tabie of deviation, and a table of 5. Ibid.. 756^1. 6. Bacon(1620),bk. 2, AphorismXI. 7. Ibid,. p. 271. 22 Darwin and Ilis Critics degree. For example, if the nature of heat is under investigation, those things that seemed hot would be listed on the fir.st table, those that lacked heat on the second, and variations in heat on the third. Only after these tables were filled out did induction actually begin. True induction for Bacon was induction by exclusion or, as it is sometimes called, complete elimination. If the relevant concepts have already been formulated and if natural phenomena can be divided into a finite number of discrete natural kinds, then induction by complete elimination is possible. All the possible causes of a kind of event can be listed and all but one eliminateci. But under such circumstances induction by complete enumeration is also possible. Bacon thought that the only induction recognized by Aristotle and practiced by his followers was induction by simple enumeration as exemplified in argument (3). But Aristotle did not consider rhe process by which the universals were abstracted from the individual as induction;it was intuition. Induction of any kind could occur only at the level of universals, and at this level both induction by complete enumeration and induction by complete exclusion (or elimination) are possible, since Aristotle believed in the existence of a finite number of discrete natural kinds. Argument (5) below is an example of an induction by complete exclusion. (5) Scalene triangles have three sides. Isosceles triangles have three sides. Equilateral triangles have three sides. (6) Man, the horse, and the mule are longJived. Man, the horse, and the mule are all bilelessanimals. Hence, all bileless animals are long-lived. Hence, all triangles have three sides. r ue Inductive Method 23 and are deductive in nature. Aristotle was cognisant of this fact.8 Many later philosophers were not. This conflict between the desire to mahe induction certain while still remaining inductive is evident in Bacon's writings. Induction by exclusion was not only a method of discovery but it afforded absolutely certain knowledge. "Now what the sciences stand in need of is a form of induction which shall analyse experience and take it to pieces, and by a due process of exclusion and rejection lead to an inevitable conclusion."0 Bacon nraintaincd that scientistswere to proceed from senscperception of the individual to the lowest universals and from there gradually, without omitting a step, to axioms of greatest generality.'n Taken literally, this view of induction would completely eliminate deduction as anything but an after-the-fact exercise,but on occasion, Bacon seems to think otherwise. Both deduction and induction have roles to play in science-"from the new light of axioms, which have been" educed from those particulars by a certain method and rule, shall in their turn point out the way again to new particulars, greater thir-rgsmay be looked for. For our road does not lie on a level, but ascends and descendsl first ascending to axioms, then descendingto works."11 It is difficult to reconcile these remarks concerning the role'of deduction in science with Bacon's earlier pronouncements about gradual ascent. If the formation of concepts or the discovery of laws is to proceed by true induction, step by step, without any jumps, how can a concept or a law be oI wider scope than the evidence from which it was derived? To the extent that true induction is possible, the collateral security of deducing new confirming instancesis impossible. Herschel, Mill, and Whewell all concurred at least verbally in Bacon's confused distinction between deduction and induction in terms of increasing and decreasing generality, 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 premisesnecessarily because of the suppressedpremise that these are all the species of triangle that there are. All speciesof triangle have been enumerated. when the suppressedpremise is added, the argument becomes deductive. Argument (6) is actually taken from Aristotle. Here, too, the cleductive nature of the inference is readily apparent. only if the three species mentioned are ail the bilelessanimals which exist is the argument valid. Both induction by complete enumeration and induction by complete elimination are possible only in a world which is divisible into a finite number of natural kinds sized the role of deduction a good deal more strongly than Bacon had. For example, I{erschel says: It is to our immortal countryman Bacon that we owe the broad announcement of this grand and fertile principle; and the development of the idea, that the whole of natural philosophy consists entirely of B. Aristotle,PosteriorAnalytics"68b15, 9 . B a c o n( 1 6 2 0 ) ,p . 1 9 . 10. Ibid., bk. 1, AphorismCIV. 1 1 . B a c o n( 1 6 2 0 ) ,b k . 1 , A p h o r i s mC I I I . 24 Darwin and Ilis Critics a series of inductive seneralizations, commencine \a,it[ the nrost circumstantially stated particulars, and carried to u.iver.sal la*,s, or axioms, which comprehend i' their statements every subordi'ate degree of generality, and of a corresponding series of inverted reasoning fÄm genäars to particulars, by which these axioms ar"etr.acedback into their ri*roresr consequences,and all ltarticular propositiorrs deduced from them 3ut it is very itnportant to observe, that the successfulprocessof scien_ . tific enquiry demands continually the alternate use of both the inductiue and d edttctiue mcthod.r, Herschel resolves tl-re conflicting roles of deduction and inductio' by observing that "in the study of nature, we must not, therefore, be scrupulous as to hoza we reach to a l<nowledgeof such general facts: providecl only we verify thern carefully rvhen once detected, we must be content to seize them rvherever they.are to be found."13 careful induction was advisable but not necessary.Hence, deductive verification woulcl be more than an empty exercise. Mill had much the same story to tell but did so with considerably more force: Bacon's greatest merit cannot therefore consist, as we are so of ten told that it did, in exploding the vicious method pursued by the ancients of flying to the highest generalization first, and deducing the micldle . principles from them; since this is neither a vicious ro. o., exploded, but a universally accredited method of moder.n science,and that to which it owes its greatest triumPhs.lr The distinction between the temporal .order of discovery and the logical order of a reconstructedlogic hacl surfaced at last. unfortunately, an awareness of this crucial distinction came in the midst of the great controver"sy bet*'een whewell and Mill and did little to improve the coherence o[ the debate. Each side accused the other of confusing proof with discovery. In following the course of this controversy, one gets the impr.essionthat neither man appreciated the importance of this distinction until after he had committed himself on too many issues.Thereafter, each tried to shore up his position without openly admitting error, while trying to expose the other's evasive maneuvers. The situation was not helped by an ambiguity in the key term "induction." whewell callecj alr processeswhich contributed to the construction of a scientific theory "induction," whereas I{erschel and Mill limited the term to inferences from the ]<nown to the unknow'. 1 2 . H e r s c h e(l1 8 3 0 ) ,p p . 1 0 4 , 1 7 4 - t 7 5 13. Ibid., p. 164. 1 4 . M i l l ( 1 8 7 4 ) ,p p . 6 8 - 6 9 . .rre Inductive Method 25 Herschel and MilI thought that both the logic of discovery and the logic of justification could be analyzed in terms of deduction and induction, ryhereasWhewell thought that no simple rules could be given for the process of discovery.15For Ilerschel and Mill the key tool in the logic of discovery and justification was induction by elimination. Darwin repeatedly made use of induction by elimination. For example, in his paper on the Parallel Roads of Glen Roy (1839), he reasoned that these roads or shelves were caused by either lakes or arms of the sea. If they were caused by lakes, then huge barriers had to be erected and removed successivelyat the rnouth of the glen. Since Darwin could not see how such huge quantities of rocl< could be moved about, he eliminated the lake hypothesis. Flence, the shelves were remnants of former shores of the sea,produced as the land was gradually raised above sea level. As Darwin's critics have been happy to point out, Darwin was mistaken. Soon after publication of the Glen Ro]' paper, Agassiz'sglacier theory was brouglrt to Darwin's attention, and Darwin immediately rcalized that huge barriers of ice provided just the sort of dams needed by the lake hypothesis. But not until 1861 was he finally forced to admit defeat, writing to Lyell, "I am smashed to atoms about Glen Roy. My paper vlas one long gigantic blunder from beginning to end. Eheu! Eheul"'u In his autobiography, Darwin added: During these two years I tool< several short excursions as a relaxation, and one longer one to the Parallel Roads of Glen Roy, an account of which was published in the 'Philosophical Transactions.' This paper was a great failure, and I am ashamed of it. Having been deeply impressed with what I had seen of the elevation of the land of South America, I attributed the parallel lines to the action of the sea; but I had to give up this vierv when Agassiz propounded his glacier-lake theory. Because no other explanation was possible under our then state of knowledge, I argued in favour of sea-action; and my error has beeh a good lesson to me never to trust in science to the principle of exclusion.lT Darwin says that the Glen Roy paper taught him a good lesson-never to trust the principle of exclusion-precisely that principle which empiricist philosophers were touting as the key feature both in the logic of discovery and in the logic of justification. Darwin was correct to doubt this principle but wrong in thinking tirat he could do without it. He continued to use the principle of exclusion throughout his later works. What he had learned 1 5 . I b i d . ,p p . 1 9 9 ,2 8 4 ; F l e r s c h e( l1 8 4 1 ) ,p p . 1 9 6 - 1 9 7 . 1 6 . S e p t e m b e6r, 1 8 6 1M , o r e L e t t e r s( 1 9 0 3 ) ,2 : 1 8 8 . 1 7 . D a r w i n ( 1 9 5 8 ) ,p . 8 4 . 26 Darwin and His Critics was not that the principle of exclusion could neuer be trusted but that it could never be trusted completely. It could, however, confer some probability on a hypothesis. It could not in actual practice make a hypothesis absolutely certain, since in the natural sciencesit is never possible to elimi_ nate all alternatives. In his Glen Roy paper Darwin had obviously overlooked the possibility of ice barriers, but there were other possibilities as weil. For example, even if the shelves had been lormed by sea action, a gradual d"c."or. in sea level would have explained ihem as welr as a gradual elevation of the land. (In point of fact, the sea level had decreased 400 feet in the preceding 1000 years.) In his coral reefs paper (1842) Darwin ex_ plained the growth of coral reefs by reference to the gradual sinking of the ocean floor. The facts, he contended, were inexplicable by any other theory. In this instance Darwin's theory was basically correct, but he had not eliminated all the possibilities-to name one, a gradual increase in sea level. (As mentioned previously, the opposite had actually occurred. Darwin also mentions certain phenomena which wourd have had the same effect as a drop in sea level.) 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 possible alternatives, bur he did think that he was justifiecl in cliscounting the current explanation in terms of special creation. I-Ie dismissed it, not because it was an i'correct scientific explanation, but because it was not a proper scientific explanation at all. "I would give absolutely nothing for the. theory of Natural selection, if it requires miraculous additions at any one stage of descent."18Darwin's reasoning on this issue will be ex_ amined later in chapter 4.1e It might also be mentioned that Bacon was no more successfulthan Darwin in eliminating all alternative explanations for phenomena he was investigating. For example, his explanation of the tides was erroneous because, in opposition to Garileo, he discounted the rotation of the earth. Galileo's explanation, however, was equally erroneous.2o The method of exclusion, when incomplete, failed to provide absolute proof for a hypothesis, but could incomplete inductions provide at least some support for a theory? Da'win thought they could. The feature of the philosophies of science professed by Herschel and Mill which would 1 8 .D a r w i n L , i l e a n dL e t t e r s( l B B 7 ) , 2 : 7 . 19. Seealsothe reviewsby Hopkinsand Wright in this volume. 20. Bacon(1620),bk. 2, Aphorisms XXXViand XLVI. i'he Inductive Method 27 be of greatest use to Darwin's critics was their contention that only logically necessarymodes of inf erence aflorded proot'. Although MiU recognized the importance of approximations in science, they were merely stages on the road to something better.zl Until this final stage was reached, proof had not been provided. The only reason for resorting to approximations was that the correct definitions had not yet been discovered, the phenomena. had not been correctly reduced to natural kinds. When they had been discerned, universal correlation was guaranteed.22In abstract sciences lihe zoology, botany and geology "a probability is of no account; it is but a momentary halt on the road to certainty, zrnd a hint for fresh experiments,"23 Mill has received considerable credit for not dismissing evolutionary theory out of hand as l{erschel and Whewell had done,2a but the credit is not deserved.'z5Mill discussesevolutionary theory in a footnote to his System of Logic, but only after treating Broussais' hypothesis about the localization of disease, Gilbert's contention that the earth is a magnet, and the suggestion that the brain be looked upon as akin to a voltaic pile. Finally, Mill says: fuIr. Darwin's remarkable speculation on the Origin ot' Speciesis another unimpeachable example of a legitimate hypothesis. What he terms "natural selection" is not only a uera causa, but one proved to be capable of producing effects of the same kind with those which the hypothesis ascribes to it: the question of possibility is entirely one of degree. It is unreasonable to accuse Mr. Darwin (as has been done) of violating the rules of Induction. The rules of Induction are concelned with the conditions of Proof. Mr. Darwin has never pretended that his doctrine was proved. I-Ie was not bound by the ruies of Induction, but by those of Hypothesis. And these last have seldom been more completely fulfilled. Ile has opened a path of inquiry full of promise, the results of which none can foresee.And is it not a wonderful feat of scientific knowledse and ingenuity to have rendered so bold a suggestion, which the fiÄt impulse of every one was to reject at once, admissible and discussabie, evelr as a conjecture?'?6 Mill's endorsement was a double-edged l<nife. While admitting the legitimacy of Darwin's procedure as a method in the logic of discovery, he 2 1 . M i l l ( 1 8 7 4 ) ,p . 3 8 7 . 22. Ibid., p. 388. 23. M;ll (1865),2:308. 2 4 . D e B e e r( 1 9 6 4 ) ,p . 1 6 4 ,a n d E l l e g ä r d( 1 9 5 8 ) ,p . 1 9 5 . 25. llimmelfarb (1959). 26. Mill (187+),p. 328. ,p, uar.wrn and His Cr.itics *:ä:1':;"i;:äl'lT'i]ij*'JT.5rii,:ii5'ä'iäi::i:l; f, ;i::::::",::g.:,::*J';:";;-J0,, ,.;..,iii.ä..f'"",,0 i*;;[,i1ffi:;ili?ffi**t*",,:**"m:rllt to supptyil';;;u.i",ll'.'o:"'"* his laws,but rre n^o ,,.. -""" ,. , .;T;;"::"::i:no "^I:,=:o:tot ,r.pe ,. $, il{li:;FtJ::,i:::::#ä-;* inthis vorum",;;;;"illii:'iffil;.*i t incrucred deeper il;'ffiäl' .?1,,:il,il,"iJ;il; ;:;#",?;**i;J"'.äi:: hllr,":.r*j:"j..j,t!i+l,vrl:',tv,.t*: i ;:lffii*::{ilH üä;li*i",t?lt *r,* fi#ü:l',r;:ff"*ä'rJ;iilx;T.Lf#i;i5.,il';1;.;';; i ;';;:;.;.;:hffiTö"'",.;*'i,.'.1'"li"t *,:*;iä:Jii.ä';ff1fi1:ffi::;#;;1 iii::IiJn,*: l::j,':iil*1*i,:*Jf"öL1rä1.^l;:i3'fi i i *:*"..:#,', fl'';h:l:'*:""*;l'' '}''ffi'.liffi,'+rf*tqüt*frfiffi :ffi.":.'':ä;;'*ä#r*n;r;:.11'"iT',:il, in whichtr,"*.ri,"ä'.r'i1'.i"iiirili"ftl*"0:r.:.,.*"ii."rr'ä.i'" i' ui pure tnduction he'lps the t"""rit"*^,"r'lrTttttt very little '' -ay.,'--"""" i\ewton ot anvor lis rottow." i;:;:ä;;i'lT[:"'*d;ttfl#: or r.i".r." il'which th"y .roi- eariY philosophers to'ri"* ,n.a Newton,s n""" .,;::".:: i -Tl.:ä#:r;H:i,,T:::il:Ti.i;,:l^.Tj:*"e i '"1':"ä?11..'*!F;il*#ffi}i'. fi:1!ffeäü'i:,'äL:ä,:f:f:iffi+1t"*x#: :#,är:'ir".1#$*m il#',*;T,äT:*n i frä#td:,*ffi#fil#,*f* ror a hypothesis, it had ''"-" er possible 'u""'' Thisprocess I r' mavevi.rphrr.. .^ r- , tr Ij:',:;:::""I,?.T::Ty j:;"g1.,-.1. o" ;" *o;;;;"''.,_-, wäs wäs repeatedrv *o**o!, citeL lil"T i: äffI.::::l; w"ri';:ö;;".; 3, T,,n"ll*0"- ; ;;;. Dew"(1818) Dew" (1818) t ä"fi.;":i:J*.H;'Tf;:l,t;.,:? if:fäJ",::;,:":':1.:". Jil.+:,:H;,i:1,1,'i'"'X'jl'.'lffif;,fu;ir:ä:'i"Ji,:XTi:J . ",:fi:l T **:*tiä{ildäi,":"r{ti:.'*ü",'1,,fi,:,:+',,jl;fl}fff ilT:':t#ilf';'*tjqg,:xri#:il'f #ä:x'""n4 ::i;x;n*rx',::;i ' ;::" ;.:**t I ä,i;"jl1.;*$p-:ä ätr *r;:.H *:ää#:A# , +1 qrErc wasnospecia '.äll,l.*Tä:l,i.rT",äi1l,T; scienco :_: _." äT$Tj:.ilil:j:,:"$fl";:,ö"::J,:ff;t':;'" iü;'i"""t::fffrJT:*:;j**:{{ijjT;yJ-fl:ü';t"l.l" "-."'u'5 Provrc ;:ff:::'ijä::ä;[::-.:1: :' sardtn this chapter . .the concerning phirosophies. Givenat d"äf ?,I.L l l t x l e v o. uru. *ro. ,; uli'ä,!lilil,u!,,11"ars.ibic,,p 31Bn zo. / lnOAr .- 5. between 0"0,..." and induction, :-ween_discove,,,"1-**r, uni .o.r."0, formation #,i |jrfft::t:t"t'." Herschel,whewell,and ;*n::fffiiH*tF1i1:]rfr*#:*,H",;*:tr; the standa.d, th"r" 30.Darwin,Juner, 1860, Ltfeandr,,,)irr.ruilr,to "u.li 30 Dalwin and Ilis Critics ,'he Inductive Method philosophers set, it might not be the theory that was at fault. what then is the current view on the philosophy of science? How does evolutionary theory, both in its original form and in its modern reformulations. measure up to today's standards? The most widely accepted moclel of scientific method.among logical em_ piricists is termed the hypothetico-cleductivemodel (H-D model). On this model, a hypothesis is formulated in some unspecified manner and then checked by deducing va'ious consequencesfrom it. If the deductions turrr out to be true, then the hypothesis is gradually confirmed. No scientific from a law, that law must be universal in form. Neither. deducibility nor the universality of the relevant laws can be abandoned without losing this eleganceand simplicity. Flowever, many putative laws in science,especially in biology and specifically in evolutionary theory, are not universal in form. hypothesis, however, is ever completely confirmed or verified. Scie.tific laws are universal in form, and not all consequencescan be crrecked.However, if one of the deductive consequencesof the hypothesis turns out to be false, the hypothesis is immediately shown to be false and must be rejected. I{ence, falsification is very easy. The I{-D model has the virtue that it does not prescribe any rigid procedures in discovery. There is no cut-and-d'ied rogic of discovery. certainly there may be methods of scientific investigation which have proved fruitful in the past and are more likely to produce results than others. For example, analogiesand models are two very effective means of discovery,while simple trial-and-error is not very efficient. But the chief virtue of the H-D model is that it recognizesthe impossibility of absorute proof for any scientific 31 Thev are statistical.statements,trend and tendency statements, and approxirlations. From the statement that blue-eyed couples almost always produce' blue-eyed children, it is impossible to deduce the eye-color of a particular child. I{orvever, it can be inferred tl-rat it is highly likely that all of the clrildren of a blue-eyed couple, ceteris paribus, will have blue eyes. The inferenceis inductive. If all less-than-universalstatements are interpreted merely as particular statements which assert o,nly that at least one subject has the predicate indicated, then the relation between verification and falsification is reversed. \/erification becomes easy; falsification impossible. But scientists do not treat all less-than-universal statements as particul:rr statements. There is considerabledifference between the claim that 99 percent of smokers wili die of lung cancer and the claim that 1 percent of them wi1l. This difference is the subject matter of statistics and probability theory. In this type of inference, neither verification nor falsification is easy. In neither case will a single observation suffice-even in principle. Populations have to be defined and samples taken. Currently, philosophers of science are trying to iormulate ivhat might be cailed a hypothetico-inductive model of science, but it is proving to be a very frustrating task. Numcrous troublesome paradoxeshave arisen, and few solutionshave been forthcoming. theory. According to the method of "inverse creduction" incorporated in the H-D model, a scientific theory can become increasingly more probable; that is all. rn inverse deduction, one reasons from the truth of specific inferences made from a law to the increased likerihood that the law is true. From the point of view of deductive logic such inferences arc fallacious-the fallacy of affirming the consequent. of course, early philoso- How appropriate are current schematizations for evolutionary theory? Darwin maintained that the Origin was one long argument and a convincing one at that: phers of science recognized the method of inverse deduction but thousht it was oniy a temporar.yheuristic device. As might be expected from its brevity, the foregoing clescription of the I{-D model is overly sirnple. IJypotheses are not tested in isolation but embedded in theories. Thus, if a decluctive consequenceof the theory turns Sorne of my critics have said, "Oh, he is a good observer, but has no llower of reasoning." I do not think that this can be true, for the Origin of Species is one long argument from the beginning to the end, and it has convinced not a fe'rv able men. No one could have written it without somepower of leasoning.3t out to be false, a single hypothesis is not falsified. I{ather, any one of severai hypothesesand observationsmay be at fault. rnstead of abandoni'g a theory upon a negative deduction, the theory is usually modified, and An argument it may be, but the traditional notions of deduction and induction were completely inadequate for characterizing it. For example, Darwin saysin the opening paragraphs of the Origin: considerable latitude is permitted in the degree of modification permissible while still terming the theory the ,,same,,theory. The elegance and simplicity of the H-D model stems from its deductive character. In order for singular observation statements to be deducible For I am well aware that scarcely a single point is discussedin this volume on which facts cannot be aclduced, often apirarently leading to 3 1 . D a r w i n ( 1 9 5 8 ) ,p . 1 4 0 . 20 rz Dar.winand His Critics conclusions opposite to those at which I have arrived. A fair resurt can be obtained only by fully.stating u"a Uofun.ing th" fr.i, il;;;;""., on both sides of each question; and this cannot possiblybe here däne-r, In a letter to Il. G. Bronn, Darwin admits, ,.you put very well and very fairly that I can in no onc i.stance exprairr the course of modification in any particular instance."ss If evolution by natural selection was to be accepted at all, it woulcr have to be "chiefly from trris view connecting under an intelligible point of view a host of facts. when we descend to details, \,\'e can prove that no one specieshas changecl; nor can we prove that the supposed changes are beneficial, which is the groundwork of the theory. Nor can we explain why some species have changed and others have not."3r As Huxley observed, the origin is "a mass of facts crushed and pounded into shape,rather than rreld together by the orclinary mediurn of an obviorrs logical bond; due attention will, *,ithout doubt, clisco'er this bond, but it is often hard to find."35 The modern reader frequently grows impatient with Darwin's method in the Origin of piling example on example, but this was the only rnethocl open to hirn given ti-restructure of evorutionary theory' This format is still characteristic of works in evorutionary theory.36 As Darwin formulated it, evolutionary trreory clid not permit verification or falsification by the simple expedient of deducing a single observational consequenceand checking it. Given Newton's equations and a few reasonably unproblematic simplifying assumptions and boundary conditions, a physicist could deduce some fairly precise observational consequenceswhich could be used to confirm or disconfirm his theory. He courd deduce where Mars should be at a precise time. Darwin's theory was neither mathematicar in notation nor deductive in form. Given evolutionary theory and the kind of data available to a biologist, no precise, unequivocar inferencesrvere possible' one could not predict how an extant spe;ies wourd evorve or retrodict how an extinct species did evolve. At best, only a range of some more or less possible outcomes could be generated. In this respect) Darwin,s theory was at a decidecl disaclvantage.The two means of verification recognized in Darwin's day were the deductive subsumption of one general law under a more general law and the deduction of specific observationar con3 1 . D a r w i n ( 1 S 5 9 ) ,p . 2 . 3 3 . _ O c t o b5e,r t 8 6 0 ,i 4 o r eL e t t e r s( 1 9 0 3 ) ,I : 1 7 2 _ 1 7 J . 34. Dawin, Lile an'dLetters(1887),ZriiOt.- - ' " 3 5 . H u x l e y( t 8 9 6 ) , p . 2 5 . 3 6 . S e eD o b z h a n s t(yt S t Z ; , M a y r ( 1 9 4 2a n d 1963). : i i i' The Inductive Method JJ sequencesof the law. Darwin's basic principles were related inferentially but not in a strict deductive hierarchy. Evolutionary theory was basically statisticalin nature. The relevant inferenceswere inductive. Charles S. Peirce was one of the few philosophers who recognized and emphasized the statistical nature of evolutionary theory. FIe saw Darwin's theory as one more application of the statistical method which Maxwell (1831-1879) had used so successfullyin physicsand Quetelet (1796-1874) in sociology.s?The work of these men and others had prepared the scientific community for "the idea that fortuitous events may result in a physical law."38 Peirce's accurate understanding of the structure of evolutionary theory is sufficiently rare to warrant reproducing in its entirety: The Darwinian cont,lol,ersyis, in large part, a question of logic. Mr. Darwin proposed to apply the statistical method to biology. The same thing has'been done in a widely dif{erent branch of science, the theory of gases. Though unable to say r,irhat the ,movements of any particular molecule of gas would be on a certain hypothesis regarding the constitution of this class of bodies, Clausius and Maxwell were yet able, by the application of the doctrine of probabilities, to predict that in the long run such and such a proportion of the n-'roleculeswould, under given circumstances, acquire such and such velocities; that there would take itlace, every second, such and such a number of collisions, etc.; and from these propositions they were able to deduce certain properties of gases, especially in regard to their heat-relations. In like manner, Darwin while unable to say what the operation of variation and natural selection in every individual case will be, demonstrates that in the Iong run they will adapt animals to their circumstances.Whether or not existing anirnal forms are due to such action, or what position the theory ought to take, forms the subject of a discussion in which questions of fact and questionsof logic are curiously interlaced.3e Although Peirce was almost alone in approving of the form of Darwin's theory, he joined the majority in rejecting selected parts of the content. He preferred Agassiz'sEssay on Classification (1859).40 In 1893 he passed the following judgment on evolutionary theory: What I mean is that his hypothesis, while without dispute one of the most ingenious and pretty ever devised, and while argued with a 37. JamesClerk Maxwell was a Scottishphysicistwhosefamousequationsrevolutionizedphysics.M. A. Quetelettrsedstatisticsin a rudimentaryway in compiling figures{or crimesand suicides;see O_uetelet(1846). Herschelreviewedthis work in the EdinburghReaieu (1850), 42 i1-57. 3 8 . P e i r c e( 1 9 3 5 ) ,6 : 2 9 7 . 39. Peirce(1877\. 40. Peirce(1931), 1;203-205. 34 fhe Inductive Method Darwin and I-Iis Critics wealth of knowledge, a strength of logic, a charm of rhetoric, and above all with a certain magnetic genuinenessthat was almost irresistible, did not appear, at first, at all near to being proved; and to a sober mind its case looks less hopeful now than it did twenty years ago.41 At the turn of the centuly, the fortunes of evolutionary theory had reached their lowest ebb. Physicists to a man had proved that the earth was not neariy as old as Darwin's theory required. Geneticists such as de Vries and Morgan were claiming that mutations were discrete, not gradual; thus, Darwin had been wrong in thinking that evolution was gradual. The excessesof evolutionists like Haeckel and the disputes concerning orthogenesis and neo-Lamarckianism had earned for evolution a decideclly bad reputation. It was more metaphysics than science.a2One would expect the situation to irnplove consiclerablywhen physicists and geneticists discoveredtheir errors, and it did, but the problem of the form of evolutionary theory remained unchanged. It was still, at best, pr.obabilistic. In the 1930's Fisher, Haldane, and Wright attempted to use the recent advances in genetics to produce a theory of evolution which was both mathematical and genetical. The unit of evolution became the gene, and evolutionary change was to be measured in terms of changes in gene frequencies. Even so, the situation with respect to verification did not irnprove much. Given modern evolutionary theory, knowledge of mutation rates, rates of difierential reproduction, and so forth, the best that a modern evolutionist could do was to provide a distribution function of possible outcomes.a3 Two alternatives seem open to us at this juncture: either revert to a hypothetico-inductive model of science or argue that evolutionary theory after a century is still inadequately formulated and that in a more finished form will conform to the lI-D model. The problem with the first alternative is that there is no H-I model. Thus, this alternative reduces to the admission that there is no reconstruction of scienceappropriate to evolutionary theory as it now stands. Biologists are currently working on the second alternative. Some are attempting to reformulate macro-evolutionary theory more rigorously so that deductive confirmation or disconfirmation is possible.aa others find evolutionary theory in terms of organisms and their interactions 4 1 . P e i r c e( 1 9 3 5 ) ,6 : 2 9 7 . 42. unfortunately,spaceprohibitsus from pursuingthe history of the reception of evolutionarytheory during this period. Peter Vorzimmer (lg70) has wiitten an informedbut uneventreatiseon these"yearsof controversy."see also provine fl971). 43. See,Ior- exalnple,Lewontin (196g) sec Hull (1974), ; for fur-thercliscussion 44. MacArthurand Wilson (i967) and Williams (I9?0). t, i: 35 too crude to permit an adequate formulation of evolutionary theory. Instead, they cail for a molecular version of evolutionary theory, hoping in this manner to fulfill the requirements of the H-D model.as This reductive maneuver is quite common in science.Whenever laws at one level of analysis appear indeterministic, analysis of the phenomena at a lower level often revealsrelations which are closer to universality. The only thing that stands' in the way of true, universal laws is accuracy of measurement and the level of analysis. It should be remembered, however, that after years of successin physics, the reductive program was frustrated at the subatotnic level. On the first alternative, philosophers of science have more work to do' They have to work out the details and general outline of a reconstruction of science appropriate to evolutionary theory in its present form. After all, notice how much better evolutionary theory looked when Peirce switched from the Newtonian to the Maxwellian paradigm. On the second alternative, biologists have more work to do. They have to produce a scientific theory consisting of universal laws which permit specific predictions. On either view, evolutionary theory and philosophy of science are still at odds' Most of this chapter has concetned the detrimentil effects of early philosophiesof scienceon the reception and accePtanceoI evolutionary theory' A few words must be said in defense of these systems.When early philosophers of science were not concerned with rigid proof and certainty, much that they said was applicable to science in general and to evolutionary theory in particular. (Compare Hopkins' strict interpretation with Fawcett's more informal treatment in this volume.) For example, Bacon provides a list of auxiliary devices to help in scientific investigation. These praerogatiue instantiarunl are much more original and applicable to actual scientific investigation than his methods of true induction' Almost everything that I-Ierschelhad to say about the discovery and verification of scientific theories-when he was not being rigorous-fits evolutionary theory perfectly. Miil is similarly reievant when he is discussing such things as multiple causation,approximate generalizations,and probable inference. Even the extensive fact-gathering encouraged by these empiricist philosophies of science was not entirely detrimental to evolutionary theory, given its statistical nature. Darwin did not waste the twenty years preceding tlre publication of the Origin. Only such a wide sarnpling of data had the slightest chance of supporting it. The relation between Whewell's phi45. Schaffner(1969). 36 Darwin and His Critics losophy of scienceand evolutionary theory is even more equivocal. Nothrng in Whewell's second-levelphilosophy of science was incompatible with evolutionary theory. He did not concur in the popular conviction that a strict 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 a deeper level in a belief which Whewell shared with Aristotle, Bacon, Herschel, and Mill, a belief in the existence of natural kinds definable 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 the most to the prevalence of metaphysical entities-essentialism. $. K. & & H" f M, $. ki N $. 3 ' Occult Qualities $], $', $' $. il i"r Nineteenth-century scientists were in agreement that all references to 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 but that his own explanation in terms of the movement of unobservable particles was perfectly acceptable. Newton thought of light as being corpuscular 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 spontäneous 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 distinction 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 experience 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 ton to l{erschel and Mill, scientistsand empiricist philosophers had a deepseated aversion to what they viewed as Scholastic occult qualities. One of the primary goals of scientists during and after the scientific revolution was to make certain that scientific concepts and generalizations were not empir'ically meaningless. The issue was not whether a scientific generalization was true but the more basic question of whether or not it was empirically rneaningful. rras known by intuition, and intuition was infallible. Observation might rvell excite intuition to act, but only intuition was capable of apprehending the tme objects of scientific knowledge-eternal, immutable essences.The most obvious objection to Aristotle's postulation of infallible intuition is that people do make mistakes. In fact, almost everything which Aristotle Aristotelian science, in the.hands of the Scholastics, had degenerated to such an extent that many putatively empiricai claims were actually immune to experimental disproof. Such notions as the hot and the moist had begun in Aristotle as observational terms. If something felt hot, then it was i'rot. But gradually these rerms took on additional dimensions. Maybe one body felt hotter than another, but that did not guarantee that it contained more of the hot. The gradual evolution of observational terms to something else is common throughout the history of ideas, but the nature of this "something else" varies- One possibility is.that the term becomes a theoretical term in a well-articulated scientific theory. For example, "force" rnay well have begun its career as an obserwational term referring to the effort a human being expends in holding a heavy object but eventually such reference became all but irreievant. Theoretical terms frequently refer to unobservable entities, but because these terms occur embedded in a well-articuiated scientific theory, indirect evidence can be obtained for the existence of the theoretical entities to which they refer. Another fate for an observational term is to become purely metaphysical. There is nothing wrong with metaphysical terms, just so long as they are openly metaphysical and do not masquerade as something else. For example, when a metaphysician refers to such tl'rings as bare particulars, he is not claiming that they exist in the same sense that trees ancl planets do. Too often, however, philosophers and scientistshave confused metaphysical terms with those that have empirical referents. The consequenceshave been less than saiutary. The terms usually singled out by Aristotle's critics as being ,,occult,, were those designed to characterize Aristotelian essences.Aristotle would have been dismayed by the claim that his essenceswere unknowable, since for him essenceswere the oniy things that were knowable in the true sense of the word. Perhaps essenceswere furthest from the level of gross observation, but they were the most l<nowablein the senseof intuitive knowledge. Aristotle's critics, of course, would reply that intuition itself was a metaphysical notion. Aristotle claimed that, at bottom, ail certain knowledee 39 himself claimed to have intuited turned out to be false. Several evasive nraneuversare possible for saving the notion of infallible intuition. The extent to which one uses one of these maneuvers determines exactly how rnetaphysicalthe notion of intuition itself becomes. One way to salvage the notion of infallible intuition is to deny the status of intuition to any process that eventuates in falschood. "You say that vou intuited that all crows are blacl<? Well, here is a white crow." "Oh, well, that must not have been intuition." Intuition was intended to assure the tluth of the premises in deductive. arguments so that the truth of the conclusionswould be assured, but ali that this maneuver does is to shift the problem back one step. Now the problem is deciding which claims oI intuition are factual and which mistal<en. A second way to save intuition is to discount al1 ex_ceptionsas monsters. Aristotle says that science deals with what happens always or for the most part, This latter qualification did not mean that scientific knowledge could bc less than universal in form. Rather, it was included in recognition o[ the existence of accidents and monsters, and science does not concern itself with accidents or monsters."That bird is white? Well, then it isn't a crow." Among normal individuals, Aristotle distinguished between essential attributes and accidental properties. Essential attributes were those characteristicswhich made a thing what it was-its defining characteristics. Accidental properties were those characteristicswhich varied in a haphazard rvay from individual to individual-the individual differences which were to be the raw material of evolution.l In addition to these accidental characteristicswhich occurred quite as a matter of course, Aristotle also recognized rare individuals completely outside the natural order-monsters. According to Aristotle, neither accidental properties nor monsters allowed of explanation and hence were not the proper subject matter of science. All natural laws were true universal generalizations. What of exceptions? They were merely accidents or monsters and could easily be dismissed. It was tl.ris Scholastic habit of monsterbaiting which ploved the greatest obstacle in the deveiopment of Scholastic science. On the modern view nf science if is nreciselv fhe "aeeidenrs" and "monsters" which call for l. See comments on Jenhin's paper. 40 Dalrvin and I-Iis Critics explanation.e It was Darwin's attention to so-called accidental variations which led to his theory o[ evolution, and it in turn demolished the Aristotelian distinction betr,r,een essentialand accidental characteristics.No characteristic is so "accidental" that it cannot become in time typical of a group. And what would have happened in geneticsif Morgan had dismissed his one-in-a-million white-eyed male {ruit-fly as an inexplicable accident? Darwin was aware of the importance of exceptions in science and also of the human propensity to ignore them: I had, also, durins rnany years, followed a golden rule, namely, that whenever a published fac.t, a new observation or thought came across me, which w'as opposed to my general results, to rnahe a memorandum of it r.vithout fail and at once; for I had found by experience that such facts and thoughts rvere far more apt to escape from the memory than favourable ones.3 He had gathered this admonition frorn Herschel, who had said in his Disc o z r r s a( 1 8 3 0 : 1 6 5 ): in any case any exception occursJ it must be carefully noted and . set aside for re-examination at a more advanced period, when, possibly, the cause of the exception rray appear, and the exception itself, by allowing for the effect of the cause, be brought over to the side of our inducI tion; but should exceptionsplove nunrerousand various in their features, our faith in the conclusion will be proportionally shaken, and at all i events its importance lessenedby the destruction of its universality. Philosopl-rers and scientiststhrough the ages have been nearly unanimous in their opinion tl-rat scientific laws l-rad to be universal in form. One way to save the universality of scientific laws is to discount all exceptions as monsters, as not propeily fitting the definition of the names of the classes of entities related in the law. Once the phenomena have been properly reduced to natural kinds, universal laws must be forthcoming.a In their investigations, scientists tend to concentrate on exceptions to their laws with the hope that such an emphasis will Iead to their improvement. Like essentialists,they hope to discover true, universal generalizations; but, unlike essentialists,they tend to change the law to accommodate the exception rather than to dismiss the exception as inexplicable. The end result of tl-re essentialist distinction between essentiai and accidental at2. This view in biology can be traced back at least to William Harvey, who in 1657 observed that the laws of nature can often be discerned by careful investigations of rareties. 3. Darwin (1958), p. 123. 4. Mill (1874), p.3BB. Occult Qualities +1 tributes is that essential attributes tend to become occult, unobservable, unknowable. Because this distinction concerns the dcvelopment of concepts rvithin a system, not some intrinsic quality of a concept from the beginning, and because there is a strong tendency to dismiss erroneous explanatory schemata as empty metaphysics, two examples will be discussed at some length in preparation for the discussion of evolutionary theory and occult qualities. These examples are Aristotle's polar principles, elements, and humors-and Newton's light corpuscles, aether, and action-at-a-distance' In the preceding chapter, Aristotle was quoted as saying that man, the horse, and the mule were all bileless animals and assuming that these ate all the bileless animals that there are. But he can also be found saying that the ass, deer, roe, camel, seal and dolphin lack gall bladders (676b26, 677.30). It would seem reasonable to infer that in a teleological system like Aristotle's there should be some correlation between lacking a gall bladder and lacking gall. These referdnces might reasonably be dismissed asa later development of his ideas, or as oversightsand errors in transcriptron or translation, but even if they accurately reflect Aristotle's view, he need not stand convicted of contradicting himself. For .Aristotle, bile was not merely the fluid secreted by the liver and stored in'the gall bladder. It was one of the four humors and, as such, part of an interconnected system o{.concepts. The basic elements in Aristotle',s science were two sets of polar principles-the l-rot and the cold, the dry and the moist. All phenomena, whether in physics, physiology, or meteorologY, were explained in the last analysis by reference to these four qualities. The four basic elements of physics were fire, air, earth, and water' Whatever properties fire had were due to its being hot and dry, air hot and moist, and so on. The four humors forrred the foundation of Aristotelian physiology. Yellow bile (or choler), like fire, was hot and dry, black bile (or meianocholer),like air, was hot and moist, and so on. In a healthy person these four humors were balanced, but when one of them gained ascendancy,iilness resulted. Therapy consisted in attempts to reinstate this balance' This system cannot be eiaborated any more fully here' The purpose of introducing it at all is to show that as a system of interconnected concepts it is not different in kind from modern scientific theories' Changes in one element in the systemhave ramifications throughout the system' For example' in Aristotle's physics of natural place, the natural place for earth was at the center. Copernicus, by placing the sun (fire) at the center, considerably simplified astronomical computation, but he overturned all of Aristotelian &il +2 Darwin and His Critics physics, and indirectly physiology, meclicine, meteorology, and so on. Aris, totelians had good reason for rejecting Copernicus, suggestion. Because bile was part of this loosely connected system of concepts, its presence or absence was not purely a matter of observation. some animal might possessbile, though none was discernible, and others rack it, though a bitter fluid could be extracted from the river. similarry, some animal might feel no colde' or moister than another animar, but because it was iower on the scale of being, it hacl to be colder and moister. .,Cold,, and "moist2' became theoretical terms connected only indirectly to our feelings of cold and moisture. Because of the subsequent history of Aristotelian science and its distance frorn us in time, modern readers might be tempted to dismiss the whole system as metaphysicar nonsense, but Aristotre,s procedure of inventing theoreticar entities which cannot be observed directly is not significantly different from modern scientific method. Today we explain the recurrent fever and chills of malaria by reference to the life cycle of a species of plasmodium rather than bv the cvclical overpredominance of blood and phregm. we berieve the action of ,t * protozoan on the blood cells can be explained in terms of the morecurar structure of DNA and RNA, and this structure in terms of molecules, atoms, and various subatomic particres. Aristotre stopped at the lever of the four qualities. Today we stop at the level of quantum mechanics. There is no doubt that our explanation is far superior to that of the ancient Greeks. Care must be take', however, in identifying the features of the mode'r explanation whicrr make it preferable to earlier explanations. It does not lie, as scientists in Darwin,s day contended, in the paucity of unobseruableentities. The elernents in Aristotelian natural scietrce became ,,occult,,, not be_ cause of the happenstance that the human organism cannot sense them directly (after all we cannot perceive ultraviolet right) but because the system in which the concepts were embecrcred was sc loosely organized that little in the way of indirect evidence was possibreeither. For exampre, ever.rthough we cannot see ultraviolet light, this light has certain effects on our skin which we can detect..Numerous predictions can be made about what ultraviolet light should do, given current theory. The four qualities and other elements in Aristotelian ph1,5is5started out as observablesand progressed gradually to the rever of unobservabres, but this deveropment was not accompanied by a con"esponding increase in precision in the sys_ temic interrelations of the more theoretic concepts and between them and possible observations. For example, a newry discovered diseasecourd be at- It. fi $r lr Nr: F' $ti $nl Occult Qualities +3 tributed to predominance of phlegm by one physician and of biie by another, and there would be no experiential way of resolving the dispute. Extreme reliance on authority became more and more the order of the day. Bacon and Newton attributed the degraded state of Scholastic philosophy both to a penchant for rash, inductive leaps and to a weaknessfor occult qualities. In order to avoid reference to occult quaiities, they proposed t. $, It tL. ': .. r' that science should make leference only to those entities, substances,or gualitieswhose character or effects could be immediately shown. For Bacorr, this proposal took the shape of fulminations against forms. Newton exlrressedthe same messagein his cryptic hypothesisnon fingo.u The manifesto was easier to proclaim than to'practice. Bacon realized that his tables could be used to abstract forms as easily as causes,and he went to great lengtl-rsto assule his readers that this was not what he was doing. Although lre refelred to "forms," he did not mean anythins like Aristotelian essences: I cannot too often warn and admonish men against applying what I say to those forms to which their thoughts and contemplations have hitherto been accustomed . For when I speak oI forms, I mean nothing more than those laws and determinations of absolute actuality which govern and constitute any simple nature, as heat, light, weight, in every kind of matter and subject that is susceptibleof them.6 The distinction toward which Bacon was groping was between concepts and laws, between defining a concept in terms of a set of covarying characters and combining concepts thus defined into empirical laws. In actual practice, Bacon's efforts at discovering causes by his inductive method differed little from those of the Scholastics.To overlook the "grand distinction" between the coexistence of characters and the successionof phenomena in time was, as it seemed to Mill, "the capital error in Bacon's view of inductive philosophy."? The conceptuai shift which made the recognition of this distinction more obvious was the change from an ontology of substancesand attributes to an ontoiogy of events. The paradigm of causationhad become one billiard bail hitting another. In Bacon's work, as well as the Scholastics',the search for laws of nature too often resulted in the enunciation of definitions,s but of equal importance 5. See discussionin the review by Wright included in this volume. 6. Bacon (1620), bk.2, Aphorism XVII. i. Mill (1874), p.381. B. The confusion of definitions and laws is still quite common. For example, 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 (1950) and Robinson (1951). 44 Occult Qualities Darwin and I-Iis Critics was the nature of the attributes referred to in these definitions. Although Bacon tried to restrict himself to observablefacts and nothing but observable 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 on superficial appearances. Like Aristotle, he argued tl-rat the earth did universally admitted theory of the undulation of light,-neither the undulation, nor the very existence of ether being ploved-yet admitted becausethe views explain so rTluch.l! \:. f {, not seem to move; hence, it did not move. Like Aristotle, he believed fin the spontaneous generation of macroscopic organisms because careful !i:. observation showed it to occur' "in animalculae generated from putrification i, as in ants' eggs, worms, flies, frogs alter rain, etc." Bacon did concede i that more carefui observation was still called for.e In Darwin's day, Sedg- i wick argued that we should accept the fossil record as we find it, not interpolate unl<nown fossils and missing strata. I-Iis catastrophic description of fossil forms and geological strata \,\'assupposedly the history of Creation. "It is not the dlearn of a disordered fancy," he asserted,"but an honest record of successivefacts that were stamned bv Nature's hanrl on the chronicle of the material wor1d."10 Could unobserwablesplay an important role in science and, if so, in what senseunobservable? One of the commonest objections to evolutionary theory was that it rested on hypotheses,on unobserwableand unknowabie phenomena. In reply to these criticisms, Darwin wanted to distinguish between theories and theoretical entities and once again took refuge in the unimpeachable authority of Newton. In a letter to Gray he objects: Your distinction between an hypothesis and theory seems to rne very ingenious: but I don't think it is ever followed. Every one now speaks of tlre undulatory tlteorlL of light; yet the ether is itself hypothetical, and the undulations are inferred only from explaining the phenomena of light. Even in the theory of gravitation is the attractive power in any way know,n, except by explaining the lall of the apple, and the movements of tlre Planets? It seems to me that an hvpothesis 1s deuelobed into a theory solelyby explaining an ample lot of facts.tt He continues along much the same vein in a letter to F. W. llutton: I am actually weary of telling people that I do not pretend to adduce direct evidence o[ one species changing into another, but that I be]ieve that this vier'v in the main is correct, because so many phenomena can be thus grouped together and explained. But it is generally of no use, f cannot make persons see this. I generally throw in their teeth the 9. Bacon(1620),bk. 2, AphorismXL and XLI. 10. Sedgwicl,, Life and Letters(1890),2:190. 1 1 . D a r w i n ,F e b r u a r yl B , 1 8 6 0 L , i l e a n d L e t t e r s( 1 8 8 7 ) , 2 : 8 0 . 45 Finally, he wrote to Lyell: With respect to Bronn's objection that it cannot be sl'rown how life '' arises,and likewise to a certain extent Asa Gt'ay's remark that natural selectionis not a aero:caLrsa,I'"vasmuch interestedby findi1g accidentally in Brewster'sLife,of Newton, that Leibnitz objected to the law of gravity becauseNewton couid not show what gravity itself is. As it has chanced, I have used in letters this very same argument, little knowing that any one had really thus objected to the larv of gravity. Newton answers by saying that it is philosophy to make out the movements of the cloch, though you do not know why the weigl-rtdescendsto the ground. Leibnitz lurther objected that the 1aw of gravity was opposed to Natural Religion! Is this not curious? I really think I shall use the facts for sonte introducloly remarks for my bigger book.13 Without realizing it, Darwin had chosen an especially inaPpropriate champion, both becausegravity, in'terpreted as an innate attraction betu'een occult quality on a very subtle every pair of particles of matter, uras ^n level and becauseNewton himself was one of the most influential advocates of the view of sciencewhich Darwin was being forced to combat' Newton stated his ideas on science very grudgingly and with more than a little petulance. They were elicited by attacks first on his theory of light and then'on his law of universal gravitation. Early in his 1ife, Newton set out a theory of light in which he claimed to prove that white light resulted from the commingling of light rays of various colors. As his notebooks show, Newton viewed these rays as being composed of "globules," or corpuscles,but when he published the results of his investigations, he was even more careful than Mendel had been in avoiding reference to the theoletical entities which he was postulating. I{e dicl, however, claim to have performed a crucial experiment which had refuted the currently popular optical theories,including Robert Flooke's undulation theory. The numerous letters published in reply to Newton's optical theory had one thing in common-they called it a "hypothesis'" The polemics that ensued clearly reveal a systematic ambiguity in the term which was still prevelant in Darwin's day and which continues down to the present. In the case of Newton, Ignatius Gaston Pardies, a professor 1 2 .A p r i l 2 0 , 1 8 6 0 M , o r e L e t t e r s( 1 9 0 3 ) , 1 : 1 8 4 . 13. February23, 1860,Lile andLetters(lBB7),2:83-84. +6 Occult Qualities Darwin and His Critics of mathematics, began his letter by referring to Newton's ingenious hypothesis concerning light. Newton replied in a model of overkill: I do not take it amiss that the Rev. Father calls my theory an hypothesis, inasmuch as he was not acquainted with it. But my design was quite different, for it seems to contain only certain properties of light, which, now discovered, I think easy to be proved, and which if I had not considered them as true, I would rather I'rave them rejected as vain and empty speculation, than acknowledged even as an hypothesis.la This terminological confusion was quickly cleared up. In his next letter' Pardies apologized for his use of "hypothesis." It l.rad been done "without any design, having only used that word as first occurring to me; and therefore request it may not be thought as done out of any disrespect."ls "Hypothesis" had been used to mean "whatever is explained in philosophy." Newton accepted Pardies' apology but went on to enunciate an additional sense of the term "hypothesis." Even if hypotheses were only statements concerning substanceswhich one might postulate as the causesof observable phenomena, Newton was opposed to them. In his Optics he had provided the laws which governed the behavior of light, regardless of whether it *,vasmade up of particles, waves, or something else. Scientistsdid not speculate about things they could not prove. Similarly, in his Principia, Newton believed that he had provided the laws which governed the movements ol material bodies. His reply to those scientists who wanted to know the nature of gravity was the same as he had made to those who had wanted him to speculateabout the nature of light: It is certainly true that no theory can explain everything. Certain features will ah.vays,Ior a time, have to be assumed.But Newton's contemporaries rvanted to know what kind of considerations led Newton and might lead them to accept gravity. Gravity really exists, but what is it that exists? \\'hat chalacteristics might it have in addition to those necessitatedby its role in the theory? Although these were precisely the questions which ' Newton asked himself, he objected to them when asked by others. He nanted to limit public debate just to those propositions "deduced from the phenomena." A more problematic phrase is hard to imagine, though it ',vasto become commonplace in the literature.l? Deduction in the strict renseis a necessaryinference, to be contrasted with induction. To deduce somethingfrom the phenomena sometimes meant that it was observed (no formal inference being involvecl) or that it was inferred from observations {induction in the broad sense). In what sensehad Newton deduced his ol)ticai and gravitational laws from the phenomena? He had hardly obsened either the various colored light rays in white light (though he had seenthe diffracted spectrum when white light was passedthrough a prism) or gravity (though he had seen bodies move in certain paths and at certain t'elocities). From these observations in the context of his general beliefs about the makeup of the universe, lte was able to infer his laws. This inference. however. fitted none of the models of induction set out in his da1'. In short, Newton would have been hard put to distinguish between his laws, which had been deduced from the phenomena, and physical hypothesesabout mechanical qualities, since at best these were precisely what his laws were. So far I have explained the phenomena of the heavens and of the sea by the force of gravity, but f have not yet assigned the cause of gravity I have yet been able to deduce from the phenomena the reasons for these properties of gravity and I invent no hypotheses.For everything u'hich is not deduced from the phenomena should be called an hypothesis, and hypotheses,whether metaphysical or physical, whether of occult qualities or rnechanical, have no place in experimental phiiosophy. In this philosophy propositions are deduced from the phenomena and rendered general by induction. It is thus we have come to l<now tlre impenetrability, the mobility, the impetus of bodies and the laws of motion and of gravity. It is enough that gravity really exists, that it acts according to the laws we have set out and that it sufEcesfor ' all the movements of the heavenly bodies and of the sea.16 1 4 . N e w t o n ( 1 9 5 8 ) ,p . 9 2 . 1 5 . I b i d . ,p . 1 0 5 . 1 6 . N e w t o n( i 9 6 0 ) , p . 5 4 7 . Newton hated to admit that certain of his plinciples were physical hypothesesabout mechanical qualities, but his critics, especially in France, went so far as to accuse him of introducing into science metaphysical hypothesesabout occult qualities. Cartesians such as Leibnitz tirelessly reminded him that gravity looked very much like such occult qualities as syrnpathy, antipathy, attraction, and hostility, the very kinds of qualities which Newton wished to exclude from science. In his eulogy to Newton, the situation as follows: Fontenelleassessed l7- For example,I-Ierschel(1841:179) claimsthat perceptionis pirilosophical deductionfrom experiment;CharlesBabbage(lB3?:57), speakso[ an observor dcducing a law from an induction of a hundred million instances; James Clerk Maxrvell (1890) claimed that his law of the distribution of electricity on the sttrface ol conductors was analytically deduced from experiment; and see the titlc of Lyell rl85i). 4B Darwin and His Critics I-Ie declares very freely that rre lays down this attraction, onlv as a cause which he knows not, and whose effects he only considers,.oäpu.", and calculates; and in order to avoid the reproach of reviving'the öccult qualities of the schoolrren, he says, that ie establishesnoie but such Qualities as are rnanif est and very visible by their phenomena, but that the causes of these Quarities are indeed occult, a;d that h.' leaves it to the other Philosophersto searchinto them.rs But the Scl-roolmenalso claimed that their qualities were manifest. After all, what is more ma'ifest than the hot and the cold, the dry and the moist? In fact, of course, the technical terms .,hotr,' .,moist," and so on, I'rad lost their original experiential connotations, but so had the notion of force in Newtonian theory. It rrad little to do with the feerins one gets when lifting a heavy object. The feature of Newton's gravitational theory which i-ris contemporaries found most objectionable was its apparent reliance on action at a clistance. Gravity acted instantaneously in the abser-rceof contact throughout all space.one way to eliminate such a counter-intuitive notion was to postulate a universal ether per-vading all space. prior to Newton, scientistshacl frequently postulated subtle fluids to explain natural phenomena, especially in biology, but such fluids were lookecl upon with some clegreeof suspicion. with the tremendous successof Newton's theory, the postulation of subtle fluids as explanatory principles became respectabre. For instance, in his review of the origin included in this volume, Flopkins justifies Lamarck,s vital fluids by comparing them with the luminiferous ether. Thus, Newton contributed unwittingly to two opposing trends in science-the rigid, overly restrictive, ultra-empirical inductive method and the almost unlicensed introduction of subtle Iluids.le There was a diflerence betwee' the occurt qualities of trre schoolmen and Newton's light corpuscles and gravity, and it was the difference which Newton himself pointed out, but for different reasons. when attacked, Newton retreated to mathematics. He invented no hypotheses.He offer.ed no mecha'isms. He simply supplied the equations which accounted for various phenomena rnathematically. (A similar retreat has occurred in this century in quantum mechanics.) Newton need not have retreated. Because he could and did provide laws which accuratery accounted for a wide nange of phenomena with a greater degree of accuracy then any previous theory, there was good reason to believe in the existence of the postulated l B . N e w t o n ( 1 9 5 8 ) ,p . 4 6 3 . 1 9 . S e eT h o m a sL l a l t ( 1 9 6 8 ) . Occult Qualities +9 rntities and qualities and to attribute to them the characteristicsthe theory required. postulate anything which Justified or not, Newton did not like to have to this score, Darwin was at On quality. occult an even slightly resembled new lorces or subno to postulate had Darwin a considerable advantage. consequences" inevitable, the almost possible, slances.FIe merely showed the vary Offspring world. organic the of fairly common observations about proare offspring More parents' sliglitly from each other and from their duced than can survive. It is reasonable to expect differential mortality as a lunction of these variations. And so on. Darwin introduced nothing that fainrly approached an occult quality, metapirysicalentity, or vital force. Although an occasional author with extreme effort was able to read his relerencesto natural selection as a reificatiou of Nature selecting,Darwin's tlieory was purely naturalistic.20 when Dar.win,s critics objected to his evolutionary theory as hypotheticai and speculative, they had in mind three features of his formulation: (1) evolution occurring so slowly that no one had observed or was likely to observeone speciesevolving into another; (2) the initial spontaneousorigin of life being in the distanr past and unknowable; and (3) Darwin's uncautious assertion that aII specieshad evolved and most likely from a single ionn. Darwin grew weary of telling people that he did dot pretend to address clirect evidence of one species changing into another. Among those rvho contributed most to Darwin's wearinesswas Huxley. Throughout their collaborarion, I{uxley steadfastly maintained that intersterilitv infallibly distinguished speciesand "until selective breeding is definitely proved to give rise to varieties intersterile with one another, the logical foundation of the theory of natural selection is incomplete."2l Dalwin believed, on the other hand, that it was clifficult "to make a marked line of separation between fertiie and infertile crosses."t' Moreover, those groups distinguis|ed by constant characters did not always coincide with those distinguished by sterility. As the years went by Darwin bccame resigned to the disagreement: I did not understand what you required about sterility: assuredly the facts given do not go nearly so far. We dif{er so much that it is no ,s" urltritg. To get ih" d.gt." of sterility you exPect in recently formed 20. See, for example,the review by Wollaston included in this volume' 2 1 . H r r x l e y( 1 8 9 6 ) ,P . v i . , o r e L e t t e r s( 1 9 0 3 ) ' 1 : 1 6 6 ' 2 2 . A u g u s ti , 1 8 6 0M 50 Darwin and I{is Critics Occult Qualities varieties seems to me simply hopeless. It seems to be almost like those naturalists who declare they will never believe that one species turns into another till they seeevery stage in the process.23 You 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, all through domestic animals, r have come to the conclusion trrat there are almost certainly several casesof two or three or more speciesblended together and now perfectly fertile together.2a You are so terribly sharp-sighted ancl so confoundly honest! But to tiie day of my death I will always maintain that you have been too sharp-sighted on hybridism.,5 Two points are at issue in the preceding quotations: the scientific issue of the sufllciency of sterility as a criterion for speciessratus and the philosophical question concerning the need for direct confirmation of theories. we cannot treat the scientific question here, since the literature is volumi" nous. All that can be mentioned is that one of the cornerstones of the synthetic theory of evolution is the biological definition of "species" in terms of interbreeding, potential interbreeding, and reproductive isolation.2. Darwin argued against intersterility as a criterion for species status and for the constancy of characters. Modern evolutionists argue against the c'terion of constancy of characters and for reproductive isoration (which in several important respectsis different from intersterility).2, The question that interests us here, however, is whether or not Huxley was justified in requiring direct evidence of evolutio' by natural selection before accepting the theory without reservation. Either Huxley is wrong in his views on the relation between direct evidence and proof or eise the majority of scientists have been mistal<e' throughout the history of science. scientific theories are accepted long before anything iike direct proof is provided. For example, when copernicus enunciated rris heiiocentric system, scientistsimmediately selected the observation of stellar parallax as the most sig'ificant test of the theory. None was observed until the 1830's-1ong after all reasonable men had accepted the heliocentric system. 2 3 . D e c e m b e2r 8 , 1 8 6 2 ,i b i d . , 1 : 2 2 5 . 2 4 . l a n u a r y1 0 , 1 8 6 3 M , o r e L e t t e r s( 1 9 0 3 ) ,1 : 2 3 2 . 25. January30, 1868,ibid., 1:287. 26. Mayr (1963). 27. For further discussion,see the cornmentson the papers by Wollastonand Fawcett in this volume. Darwin mentioned isolation in the'origin' (1859:105) but Iater largelv ignored it. Not so Mayr (1963). peter vorzimm"e, itozol Jiräurr", these issuesin his book on Darwin. /.,dr_i'r\qgir*\ \n ,r'1,.; I 1;1;1;1it,1..\'1.5 i ui,EfdfJlllllilt , not untii recently has anything like the observation of the evoluof new speciesof muiticellular organisms been observed. (The developof speciesby polyploidy has been observed on occasi.on,but this is a Darwinian method of evolution, and the evolution of new species :bacteria is commonpiace.) Yet, few reasonable merr withheld consent itlu theory that species have evolved and that -natural selection is the icf {if uot the only) mechanism involved. or example, even in Darwin's own day, F. J. Pictet contended in his of the Origin of Species (1860) that he would not accept Darwin's dtductions until he saw for himself the evoiution of a new organ' By 1864 t had been converted and in 1866 published a paper in support of ionary Lheory (Pictet and Humbert, 1866). Needlessto say, the direct he required had not been supplied. Instead, he had been convinced ttry the numerous indirect proofs of evolutionary theory. On this score special n and evolution by natural selection were on different footings. No ftra seen a new speciesevolve anymore than they had seen.onespecially but unlike the special creationists,Darwin had presented a mechafor evolution. Certain implications of his theory could be checked :rana lis theory as a whole gradually confirmed or disconfirmed without i,rbe direct observation of speciesevolving. Special creation was little more i;i" ,than a bald assertion. Whether as a natural event lacking any scientific eiplanation or as a supernatural event, special creation could be checked ,Qälyby direct obseiwation. As Darwin was to discover in his attempts to lesswell-organized .q1gueagainst the "theory" of speciai creation, ib was even ,thanAristotle's doctrine of polar principles and humors. i, ,Confirmation of a scientific theory by reasonably direct means is always , welcome,but such confirmation comes long after the theory has been establiuhedbeyond all reasonabledoubt. Empiricists had performed a worthwhile s*n'ice in emphasizing the continuing role of experience in science, but, i ar l{erschei obserwed: "Some things we come to believe not through obserl'v:ltion but by demonstration-speed of light, action at a distance in gravity, the size of the sun, etc."'E As this list indicates, the things we come to believe thr"ough demonstration, or indirect proof, are a mixed bag. The dilficultl, lies in distinguishing between theoretical entities and those that lack any empirical referents. If the issues had been more clearly drawn at the time, it would have been dificult for Darwin's critics to charge that natural selection was other than observable-as observable as a phenomenon can get. The situation was somewhat more equivocal with resPect 28. Herschel(1830), pp. 23-24. t: 52 Darwin and FIis Critics Occult Qualities to the initial spontaneous generation of living creatures from nonliving su!512n6s5-lut not very. Before Dar-win, the common ploy in dealing with the origin of by natural or supernatural means was to dismiss the question as with events that occurred too long in the past ever to be known. scientists wexe free to believe as they saw fit, and they generally tion and extinction of the past and present inhabitants of the world should have been due to secondary causes,like those deterrnining the birth and species dealing I{ence, saw fit to believe in accordance with revealed religion. "The mystery of creation is not within the legitimate territory of science." Theology must be assiduously excluded from the dynamical sciences but was a necessary adjunct to the historical sciences,es Darwin was presented with a dilemma. The currentiy popular doctrine of the miraculous creation of species,a flashing together of elemental atoms 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 forced to introduce "new powers" or "principle of improvement," he would reject his theory of natural selection as "rubbish."sl Darwin felt himself $r il $' N N. i il I li I i, committed to a naturalistic explanation of the initial origin of species. ! Ile had none. To make matters worse, the naturalistic explanation for ii s the origin of life, the spontaneous generation of life, had a decidedly bad f, reputation in scientific circles.s2The spontaneousgeneration of multicellular organisms had been disproved after years of laborious effort, just in time for its advocates to switch their allegiance to microbes. It was Darwin's il i., i misfortune to propose his theory of evolution, which seemed to necessitate il the spontaneous generation of the original forms of life, at the same tirne that Pasteul was beginning to route spontaneous generation from its last t' 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, i of lile by means of a supernatural metaphor. "There is a grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one."33 Later he added, "by the Creator.', Such a reference to the diety, however, did not necessarily commit Darwin to a miraculous creation of life. "To my mind it accords better with what we know of the laws impressed on matter by the Creator, that the produc29. Whewell ( 1840), 3:639; see also Wollaston,s review in this volume. 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. pictet, Sedgwick, Owen, and 32. See, for example, the papers by Wollaston, . Agassiz in this volume. 33. Darwin (1859), p. 490. 53 I l I i i death of the individual."sa In this opinion Darwin agreed with the leading authorities of the day. With one or two exceptions, the author of every review in this collection concurred with this view of God_as acting through exceptionlesslaws, not by rniraculous special creations. Even so, Darwin was unhappy that he had gone so far and wrote to Hooker, "But I have long regretted that I truckled to public opinion, and used the Pentateuchal term of creation, by which I really meant cappeared' by some wholly unknown process."35 Darwin was never to resolve this dilemma, but there is little doubt as to which alternative he preferred. As iate as 1870, he can be found saying: Spontaneousgeneration seemsalmost as great a püzzle as preordination, I cannot persuade myself that such a multiplicity o{ organisms can have been produced, like crystals, in Bastian's solutions of the same kind. I am astonished that, as yet, I have met with no allusion to Wyman's positive statement that if the solutions are boiled for five hours no organisms appear; yet, if my memory servesme, the solution when opened to air immediately becomesstocked. Against all evidence, I cannot avoid suspecting that organic particles (my gemmules from the separate cells of the lower organisms!) will keep alive and afterwards multiply under proper conditions. What an interesting problem it is.36 It is frequently argued that evolutionary theory was wasted motion unless Darwin could also show how the first forms of life originated. In his defense, Darwin once again sought refuge in the authority of Newton: [Bronn] seems to think that till it can bö shown how iife arises it is no good showing how the forms of life arise. This seemsto me about as logical ' (comparing very great things with little) as to say it was no use in Newton showing the laws of attraction of gravity and the consequent movement of the planets, because he could not show what the attraction of gravity is.37 In this instance Darwin's defense is apt. Newton, like Darwin, felt that he had accomplisheci something by his theory even though he had left somequestionsunanswered; e.g., questionsconcerning the nature of light and the cause of gravity, It is interesting to note that Mill, at least, agreed with 34. Ibid., p. 48B. 35. March 29, 1863,Life and Letters(1887),2:202-203. , o r e L e t t e r s( 1 9 0 3 ) ,l : 3 2 1 . 3 6 . J u l y 1 2 , 1 8 7 0M 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 4'Teleology been more prudent not to have put it in, I would not strike it out, as 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 were willing to admit that varieties may have arisen through natural selec. tion, but one must not carry things too far. These varieties never strayed from the confines of their species (Pictet). Or perhaps, as Forbes and Teleology had been part of the conceptual frameworh of Western science from ancient Greece until the time of Darwin. Natural phenomena might be governed by scientific laws, but it was the Creator who had instituted ii:i them. Galileo and Newton replaced ono physical theory with another, but others suggested, there were several centers of creation, and then dispersal, irrr they 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 systems like Forbes's failed to gain wide. the appearanceof the Origin of Specieswas so fundamental that it certainly spread acceptance. There was considerable wishful oratory about moderatiorr$$', the title of a conceptual revolution. The problems which arose deserves in all things-a little bit of evolution tempered u'ith a little bit of specials.\, $]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 guidrve will be concerned with the difFculty which scientistshad in reconciling ance-but at bottom the two positions were incompatible. As soon as a $^ 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, termed teleologicalwas 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 explanation Teleology,the belief that things in the empirical world "strive" to attain being given for all species.Unlike Wallace, Darwin insisted on telling a är.' ends, is one of the most influential and misunderstood doctrines in the totally consistentnaturalistic story or none at all. $f' history of philosophy. In one interpretation, teleology entails a universal 3 8 . M i l l ( 1 9 1 0 ) ,2 : 1 B l ; s e ea l s oF a w c e titn t h i sv o l u m e . c.onscious being ordering everything for the best. As Plato Put it: "I heard 39. December 25, 1859,Lile and Letters(1887),2:46. some one reading, as he said, from a book of Anaxagoras, that mind was u r' $ $' Hr', K $i $, $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 For the Platonic doctrine of external teleology, Aristotle substituted the subtler view of immanent teleology. For Aristotle the ends were internal $' {.,' il' lil[: f.. fi I. Plato.Plnedo.St. 96-99. 56 Dalwin and His Critics to the subject' Individuals did what was best for themselvesby themselves. Every natural kind (or species) had a static, immutable essenceas rts formal cause' These essencesmade a thing.lvhat it ,"vas.These essences iu turn also serwed as final and efficient causes. The end toward which a' things strove was to realize their olvn essenceas fully as possible. ,,[For] any living thing that has reached its normar development and which rs unmutilated, and whose mode of generation is not spontaneous,the most natural act is the production of another like itserf, an animal producing an animal, a plant a plant, in order that, as far as its nature allows, it may partake in the eternal and divine. Trrat is the goal towards wrrich aI things strive, that for the sake of which they do *h]tsoerrer trreir nature renders possible."z Both of these versions of teleology can be interpreted to be exciting, substantive claims about the empirical world. In these interpretations they have been shown to be untenable. For example, accordin.gto external teleology, given a knowledee of the orde'ing mind, one should be abre to infer rvl-rat tl-re empirical world must be rike, ancl conversery,given knowledge of the e'rpirical world, one should be abre to infer the crraracter of the ordering mi'd. If the universe is a perfectly running mechanism rvith a place for everything and everything in its place, rhen one type of mind is implied. If it is a shoddily constructecrmechanism which needs constant tinkering, another type of mind is implied. what externar tereologistsdid not rike about evolutionary theory was the type of mind it irnplied. God coulcl have constructed the worlcl so that species evolved by natural selection in the struggle for existence, bur that ki'd of God dicl not seem especialry worthy of love and veneration. Evolutionary theory had even more devastating consequencesfor immanent tereorogy. If essencesare static and if in general the goal toward whicrr all things strive is to realize their esserrce, then the wholesale progressive change entailed by evorutionary theory is impossible. If evolution has occurred, then either essencesare not static or else things must strive, not to furfilr their own essence,but the essence of some other species. Both versions of tereology also have more sophisticated interpretations, but with these interpretations they become vacuous. An advocate of external teleology might be led to say that whatever the larvs of nature turn out to be' God did it' He never suspends these laws in divine intervention, and these laws reveal nothing of his character. An advocate of immanent teleology might assert that all it takes for the worrd to be teleolosical 2. Aristotle,De Anima, 415" 26. Teleology i ,il for regularitiesto exist. The emptinessof thesepositionsis all too apparent, .".but they were the positions to which the proponents of teleology were at last driven. Darwin's theory was one of the chief instruments in the ' final trivialization of teleology. Thanks largely to the efforts of Thomas Aquinas, Aristor_elian metaphysics,physics,and natural history were incorporated into Church dogma. Tlrrough the years, however, Aristotle's metaphysics took on a decidedly ' Platonic caste. God was not merely a detached, impersonal first and final . . cause.but an overseerwho actively participated in the affairs of the world. He both instituted the laws of nature and periodically suspended them in miracles. Copernicus and Galileo had to combat the Aristotelian physics of natural place, but they did not attack either the metaphysicsor theology of.Church doctrine. God still instituted the laws of physics and still suspended them on occasion, but these laws were the laws of Newton, not Aristotle. But of even greater significaflce, Newton's laws required the continued and continuing efforts of God in their operation. Newton was anxious to reconcile physics with theology, and his instrument was Richard Bentley (1662-17+2).3 Bentley did for Newtonian physics what Aquinas had done for the physics of Aristotle. In "A Confutation of Atheism from the Origin and Frame of the World" (1693), he argued that Newtonian physics was not only compatible with the existence of God but also necessitatedit. Bentley's arguments all follow the sarne format. Certain phenomena were derivable Irom Newtort's laws, e.g., the earth traveling around the sun in an ellipse. Other phenomena were not derivable from Newton's laws, e.g., the sun bcing luminiforous and the other bodies in the solar system opaque, the distancesof the various planets from the sun, and the inclination of the earth's axis of rotation to its plane of revolution. Now that Aristotle's physics of natural place had been abandoned, these phenomena had no explanation in terms of natural law. They had no secondary causes. They appeared to be "accidental" features of the universe. Yet they had to be precisely as they were in order for the earth to support life. If the earth were farther away from the sun, then it would be too cold to supPort life. If nearer, it would be too hot. If the earth's path had been more elliptical, the extremes in temperatur-eon earth as it revolved around the sun would be too great. If the earth's axis had not been inclined to the plane of its orbit, parts of the earth would be too hot to support life and others too cold. If the earth revolved around the sun more slowly, the seasons 3. Lilre Whewell,BentleywasMasterof Trinity College,Cambridge(1700-1742). 58 59 Darwin and His Critics Teleology would be too long. If rnore quickly, too short. And so on. All these phenomena had to be as they were if life-- especially man-was to exist. Their. disposition did not follow fi'om Newton's laws. Flence, either they occurred As Aristotle observed, instead of organisms' being so well-organized and rveli-adaptedbecauseit was of their essenceto be so, "such things survived, being organized spontaneouslyin a fitting way; whereas those which grew by accident or else God did it. The chance coincidence of so many phenomena was extremely implausible. Flence, God was responsible. The existence of life was good. I{ence, God was good. otherwiseperished and continue to perish." Aristotle immediately dismisses such a ridiculous contention. "Yet it is impossible that this should be the tlue view. For teeth and other material things either universally or nolmallycome about in a given way; but of not one of the results of chance or spontaneity is this true."? Whenever anything occurs regularly, it must be becausethe formal and final causescoincide. Because an organism is what This Neoplatonic world-view was to find favor among such biologists as Cuvier, Owen, Agassiz, and von Baer. Space was God's sensorium, gravity his consciouswill, and each speciesa divine thought. Even an empiricist like Flerschel concurred in this ontology, hoping to combat the more radical empiricism of Locke and Hume and the materialism of Laplace. According to llerschel, falling bodies are urged .to the earth's surface ,,by a force or it is, it produces teeth as they should be. The haphazard production of numerous alternatives and the elimination of those that are not fit occur too irregularly to be part of the natural order. An identical story can be told for William Whewell, with one minor complication. FIe somehow had to reconcile his own advocacy of final causes with Bacon's "barren virgin" quip. Whewell's solution was to argue that final causes should be excluded from physical inquiry but were perfectly legitimate as the results of such inquiry. Final causeswere barren because effort, the direct or indirect result of a consciousnessand a zolll existing someu,tlzere,though beyond our power to trace, which force we term grauity."l In his Bridgewater Treatise, Whewell updated Bentley's arguments for God's existence. In reading I{erbert Mayo's The Philosolthy o.f the Liuing (1838), Darwin was incensed over Mayo's contention that Whewell was they themselves were the fruits of the labor.s God ordered the universe according to his divine plan, and it .was the goal öf science to discover this plan. Any explanation in terms of the perishing of the unfit and the survival of the fit was inconceivable: profound "because he says length of days adapted to duration of sleep of man!!! whole universe so adapted!!! and not men to Planets.-instance of arrogance!!"5 The Bridgewater Treatises were published because scientists had been gaining the reputation of being materialists, determinists, If the objector were to suppose that plants were orginally fitted to yeals of various lengths, and that such only have survived to the present time, as had a cycle of a length equal to our present year, or one which could be accommodated to it; we should reply, that the assumption is too gratuitous and extravagant to require much consideration.e and atheists, especially in France with the workl of D'Alembert, Diderot, de la Mettrie, Laplace, and Voltaire. Whewell was pleased to do rvhat he could to combat the growing slander by showing the mutual dependence of science and religion. "My prescribed object is to lead the friends of religion to look with confidence and pleasure on the progress of the physical sciences,by showing how admirably every advance in our knowledge of the universe harmonizes with the belief of a most wise and good God.',u Periodically, proponents of teleology, whether of the immanent or tire external variety, entertained a possible alternative explanation for the aoaptation of living creatures to their environments-the survival of the fit. 4. Herschel(1833), pp.221-222. 5 . D e B e e r( 1 9 6 0 ) ,p . 1 3 4 . 6. Whewell (1833), p. i; though Whewell'sBridgewarerTreatisewas Volume III of this series, it was the first to appear in print. The complete title of this series was TIte Bridgeuater Treatises on the Power, Wisdom and Goodness of God, as in the crcation. Dach contribution will be cited separately by the -Manifested title of that volume. We have only a fragment of Charles Babbage,i (1S37) etror* which does not form a part of the Bridgewater Treatises, even tho'gh it bears the title The Ninth Bridgeuater Treatise. Lilre a true philosopher, Whewell went on to hedge his bet. Even if adzptations did come about by such a gratuitous and extravagant mechanism, "it does not remove the difficulty. Ifow came the functions of plants to be periodical at all?" I Prior to the publication of the Origitt, philosophers and scientists had some justification for rejecting nonteleological explanations of adaptation, since there was no alternative explanation. Lamarck's theory came closest to supplying a mechanism fol adaptation, but few were willing to accept it, both because of its own weaknessesand becauseof the inordinate influence of Cuvier. After the Origin, however, the reactions of philosophers 7. Aristotle,Physics, bk. II, ch. B. B . W h e w e l l( 1 8 3 3 ) ,p . 1 8 0 . 9. Ibid.. p. 27. 60 6i Darwin and l{is Critics Teleology and scientistswere not much different. Mill, inhisTlzree Essayson Religion written during the decade following the publication of the Origin and published posthumously in 1874, still found the argument from design preferable to evolution by natural selection: Flerschel's position on these matters was typical. In his 1861 edition of Physical Geography of tlte Globe, he added the following comment on Darwin's theory: I regret to say, however, that this latter half of the argument is not so inexpugnable as the former half. Creative forethought is not absolutely the only link by which the origin of the r,r'onderful mechanism of the eye may be connected with the fact of sight. There is another connecting link on which attention has been greatly fixed by recent speculations, and the reality of which cannot be called into question, though its adequacy to account for such truly admirable combinations as some of those in Nature, is still and will probably long remain problematical. This is the principle of "the survival of the fittest." Mill continues: Of this theory when pushed to this extreme point, all that can now be said is that it is not so absurd as it looks, and that the analogies which have been discovered in experience, favourable to its possibility, far exceed what any one could have supposed beforehand. Whether it wiil ever be possible to say more than this, is at present uncertain. The theory if admitted r.r,ouldbe in no way whatever inconsistent with Creation. But it must be acknowledged that it would greatly attenuate the evidence for it.ro Darwin's arguments in the Origin are mere analogies,whereas the argument from design r.r.asa genuine inductive argument. "In the present state of our knowledge, the adaptions in Nature aflord a large balance of probability of creation by intelligence." Many philosophers and scientists were willing to accept evolutionary theory if only Darra'in u'ould admit divine providence. Without it they felt trapped between inexorable law and blind chance. The terminology of this position varied, but the messagewas always the same. Some maintained that some phenomena were lawlgoverned, other lthenomena not. Others maintained that ail phenomena r,r.erelaw-governed. In either case, God instituted these laws and guidecl their action. A universe governed by divinely instituted law did not seem so cold and barren. Add periodic mir-aclesand the world-picture became evell rnore intimate. Lxclude God, and both accidental and larv-govemed phenomena bccame equally "accidental," given the peculiar telminology of the time.11 1 0 . M i l l ( 1 9 6 9 ) ,p p . 1 7 2 ,1 7 4 . 11. For example, see the review and Wright in this volume. by von Baer and the exchange between Mivart This was written prior to the publication of Mr. Darwin's work on the Origin of Species,a work which, whatever its merit or ingenuity, we. cannot, however, consider as having disltroued the view taken in the text. We can no more accept the principle of arbitrary and casual variation of natural selection as a sufficient condition, per se, of the past and present organic world, than we can leceive the Laputan method of composing books (pushed ä outrance) as a suficient account of Shakespeare and the Principia.t" Herschel is repeating l-rischarge quoted earlier that Darwin's theory was the law of higgledy-piggledy. Evolution by random variation and natural selectiondid not exhibit the mathematical regularity and simplicity characteristic of physical law. The laws of physics wele worthy of God's authorship, just as Hamlet and Macbetlt were worthy of Shakespeareand the Principia worthy of Newton. Darwin's theory implied a God who would composea book by randomly striking the keys of a -typewriter until something turned out. Herschel did not want to deny that evoiution might occur by law, but it had to be a la'w worthy of God. Equally in either case, an intelligence, guided by a purpose, must be continually in action to bias the directions of the stepsof change-to regulate their amount-to limit their divergence-and to continue them in a definite course. We do not believe that Mr. Darwin means to deny the necessity of such intelligent direction. But it does not, so lar as we can see, enter into the formula of this law; and without it we are unable to conceive how far the law can have led to the results. On the other hand, we do not mean to deny that such intelligence may act according to a law (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 succession;or one more general, taking the fonn when applied to our own planet, and including all the links of the chain which have disappeared. But the one lalv is a necessarysupplernent to the other, and ought, in all logical propriety, to form a part of its enunciation. Gr-anting this, and with some demur as to the genesis of man, we are far from disposed to repudiate the view taken of this mysterious subject in Mr. Dar-r.r,in'sboolc.13 12. Flerschel (1861), p. 12; see von Baer's review in this volume for an expansion on this reference to Gulliuer's TraaeLs. 13. Iferschel (1861), p. 12. 62 Teleology Dar-lvin and His Critics believe that there is a bit more interference by the Ct'eator in the construction of each species than in the course of the planets. It is only ou,ing to Paley and Co., I believe, that this more special interference is thought necessary with living bodies. But wc shall never agree, so clo r-rottrouble yourself to answer.1s A quick reading of the preceding paragraph might lead the reader to think tl.rat Flerschel is saying much more than he is. Herschel pleads for a supplementation of Darwin's laws by some reference to intelligent dilection, but what does he suggest? A description of phylogeny! Darwin was 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 honestly whethcr what you are thinking applies to the endlessvariations of domestic productions, rvhich man accurnulates for his mere fancy or use. No doubt these are all causedby some unknown larv, but I cannot believe they were ordained Ior any purpose, and if not so ordained under domesticity, I can see no reason to believe that they were ordained in a state of nature' Of course it may be said, when you l<ich a stone, or a leaf falls from a tree, that it was ordained, before the foundations of the world were laid. exactlv where that stone or leaf should lie. ln this sensethe subject has no interest for me.16 in which case Darwin felt obligated to deny it. If God were all-good, all-knowing, and all-powerful, then one would expect that organisms would tend to vary in directions advantageous to their survival. Darwin found no evidence o[ such directed variation. As far as Darwin could tell, variations were "chance," they occurred "in all directions." By .these claims Darwin did not mean that variations w,ere uncäused. Rather he meant that whatever laws governed variation, they were currently unknown and to the best of Darwin's knowledge they were not teleological. That is, there was no correlation between those variations which an organism might need and those it would get. The God implied both by cvolution and the current state of the organic world was capricious, cruel, arbitrary, wasteful, slipshod, and totally unconcerned with the welfare of his creations, a god reminiscent of the Old Testament, not nineteenth century natural theology. I $. ! ! There seems to me too much misery in the world. I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of Caterpillars, or that a cat sl.rould play with a mouse. Not believir-rg this, I see no necessity in the belief that the eye was expressly designed.ln One might argue that God moves in strange ways and that he is guiding things, though we cannot discern his plan. I-Iowever species evoive, that is the way he planned it. Darwin found this position empty verbiage. He saw no reason to utter such pious inanities. No mention is made of intelligent direction in the formula of evolution by natural selection, but neither did it enter into the formula of the law of universal gravitation. In a series ol letters, Darwin tried, with little success,to make his position clear to Lyell: No astronomer, in showing how the movements of planets are due to gravity, thinks it necessaryto say that the law of gravity was designed that the planets should pursue the courses lvhich they pursue. I cannot 14. f)arwin,May 22, 1860,Lif e andLetters( 1BB7)2: 105. 63 lr $ It n * Will you honestly tell me 1o,.,i f should be really much obliged; whether you believe that tl-re shape of my nose (eheu!) was ordained and "guided by an intelligent cause"? By the selection of analogous and less differences fanciers make almost generic dif{erencesin their pigeons; and can yor.rsee any good reason why the natural'selection of analogous individual diffelences should not tnalie a nerv sPecies?If you say thai God ordained that at some time and place a dozen slight variations should arise, and that one of thern alone should be preserved in the stluggle for life and the other eleven should perish in the first or few generations, then the saying seems to me mere verbiage. It comes to merely saying that everything that is, is ordained.tt At one tirne God had played an important role in physics,but gradually his function had been eroded, until reference to him was little more than pious honorifics. It is often said that evolutionary theory brought an end to the practice of including God as a causal factor in scientific explanations' A more accurate characterization is that it demonstrated forcefully that this day had already passed.The architects of the clemiseof teleology were not atheistic materialists but pious n-renlil<e Herschel, Whewell, and Mill, rvho thought they were doing religion good service by limiting tl're domain of the accidental and of the miraculous. To them the more the empirical rvorld was shown to be governed by secondary causes acting according to God-given laws, the more powerful and ominiscient God was shown to be. With rare exception, every author included in this volume, whether , o r e L e t t e r s( 1 9 0 3 ) ,l : 1 5 4 . 1 5 .J u n e1 7 ,1 8 6 0M 1 6 .A u g u s t1 3 , 1 8 6 1i,b i d . ,1 : 1 9 2 . , o r e L e t t e r s( 1 9 0 3 ) ,1 : 1 9 3 . 1 7 .A u g u s t2 1 , 1 8 6 1 M 6+ in favor Dalwin and I-Iis Critics of evolutionary theory or against it, strongly supported of God's relation to natural accidental, put had be shown not to be accidentar, either beof God or by subsuming made thereby limiting constant God governing "The one which the world sistent, is the conception Darwin of is inco'sistent will. with on the relation with Tlie one which betwee' from scie'ce, wheweil of a is conlaws.,,1s science ancl religion for his theory. He prefaced quotations of the As Mill is the conception of a God governir-rg the r,vorld by invariable to gain a fair hearing the origin them under law. on the domain of theism, one consiste't by acts of variable used this position in an attempt edition inroads the need for God's direct intervention. it, there were two conceptions one inconsistent. this view phenomena. Accidental occurrences could cause of the direct inter-vention Pliysics since Ne*'ton Teleology and the fir.st Bacon to the shourd be placed in the path of scientific inquiry because no larv could be discovered r.r'hich was contrary to God's will. In the sixth editiorr he added a third quotation to this same effect by Bishop Butler' All Darwin wanted to do was to extend the domain of secondary effect that no irnpediment causes to include the creation of species. Although in the past the creation of species had been considered miraculous and outside the realm of lziw, so had many other phenomena which had been shown to be law-governed. Darwin u'as acting within the currently acceptecl tradition of expanding the realm of law. wl'rewell recognized wanted that to retain the creation such an explanation of species as miraculous was not a tenet of physical but he science but of natural theology.rs wheu'ell's bare recognition that the origin species was even susceptible to a naturalistiö explanatio' gave heart Lyell, who had pr-oved so uncharacteristically timid on the evoiution of to species' In a letter to I{erschel, he r,r,rote, "whewell, in his excellent treatise Sciences, aprlears to me to go nearly so far as to contemplate the possibility at least of the introcluction of fresh species being gov- erned by general laws."2o There were those like sedgwick and Agassiz who wished to retai' to lend significance to their teleological clairrs. A majority losophers and scientists, however, gradually abandoned the notion of creation but still wished to retain teleology as a significant doctrine. special of phispecial white- head, Dewey, and Peirce all espoused creative evorution. walrace, Asa Gray, 18. Mill (1969), p. 135. 19. Whewell (1837), 3:640. 2 0 . L y e l l , M a y 2 4 , 1 8 3 7 ,L i f e o l L y e l t ( l B B l ) , 2 : t Z , and Lyell belabored Darwin with argurnents for admitting divine provrdence, especially with respect to man's mental and moral faculties. For exarirple,Lyell hailed Wallace's suggestion that "there be a Supreme Will and Power which may not abdicate its function of interference but may guide the forces and laws of Nature." What these men did not realize ivas that by pushing God further and further in the background as the unknowable author of natural 1aw, regardless of the nature of these 'laws, they frad prepared the way for his total expulsion. Like l{ant's Ding an rirlz, he was remote, obscure, unknowable, somehow underlying everything and very important but of no conceivable consequenceto any endeavor. 'feleological supplements were as otiose to evolutionary theory as they were to contemporary versions of Newtonian theory. The superficiality of teleological claims in a deterministic universe was not totally lost on the educated public. For example, one writer observed with respect to tl-rehabit of naturalists to interpolate tl-reir writings with references to God: "It appears to them that, unless they clrag the Creator into every second paragraph, their essaywill not possessthe necessaryreligious veneering for the public t;ste."21 Darwin was not impervious to the pathos in the dile-ttto which confronted his colleagues. Neither a world ruled by deterninistic laws nor one in which chance played an important role seemed bearable. Even though Darwin had not intended to write atheistically, his theory robbed rhe traditional solution to this dilemma of all its plausibility. The closest Danvin came to a resolution of the conflict between teleology and the facts of natural history was his suggestion that God instituted the general larvs,whereas the details were left to chance: of on the Inductive creation 65 My theology is a simple muddle; f cannot lool< at the universe as the result of ülind chance, yet I can see no evidence of beneficent design, or indeecl of design o[ any ]<ind, in the details. As for each variation that has ever occurrecl having been preordained for a special end, I can no more believe in it than that the spot on which each drop of rain falls has been specially ordained.22 On the other hand, I cannot anyhow be content€d to view this wonderful universe, and especially the nature of man, and to conclude that everything is the result of brute force. I am inclined to look at everything as resulting from designed laws, with the details, whether good or bad, 2 1 . A n o n y r n o uP s ,o p u l a rS c i e n ' cRee u i e w( 1 8 6 6 ) ,5 : 2 1 5 ' , o r e L e t t e r s( 1 9 0 3 ) ,1 : 3 2 1 . 2 2 . J u l y 1 2 , 1 8 7 0M 66 Dalwin and His Critics 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 others. But it should be recalled that by .,chance" Darwin meant by laws not as yet known. Darwin,s solution was. a circuitous of determinism. Interpreted realistically, teleology was incredible. Given Essences i., sufficiently sophisticated interpretation, it was of no relevance to science.2a .teleology.permeated Western thought, essentialism was even more Per' . The number and variety of metaphysical systems generated on the and in England was staggering. Realists maintained that the existed in nature, perhaps in individuals thernselves (Aris) , or both in nature and in the mind of the creator (Neoplatonists) . ts süch as Cuvier, Owen, and Agassiz are often referred to 23. Darwin, May.22, 1860,Lile and Letters (1g87). 2:10524. The issr.reof teleology has had a recent ."r,,.jer"" brrt in entirely different terris. several and biologists have attempted to analyze ieleological -philosophers systems _naturalistically in terms of genetic pl.ograms, negative feedbacL, urä so o n . S e eM a y r ( 1 9 6 1 ) a n d C a n f i e l d ( 1 9 6 6 ) . 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 maini.ng that only matter exists (minds are merely brain processes). Although i: 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. dichotomy cuts across the preceding distinctions. empiricist-rationalist rfihe 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 frey 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. 69 Darwin and FIis Critics Essences Alvar Ellegärd (1957 and 1958) sees the disagreement over the immutability of species as a conflict between empiricist and "idealist" philosophies of science. Although our story would be much neater if this were ls so an unfathomable chasm . . The universe, so far as known to us' of cases all true in is t$nstitlrtecl,that whatever is true in any one case, I(inds description' a certain description; the only difficulty is, to find the ' '"3 are Classesbetween which there is an impassiblebalrier 'fhough Mill's empiricist ontology did not directly require the existence proof of discrete natural kincls, his logic of justification clid' At bottom, E' was suppiied by eliminative induction. "Either A, I), or C can cause be to A ancl B are absent. Hence, C must cause E'" For this inference specibe must event of l<ind of a certain causes alternative the r.aiid, all of of this fred and all but one eliminatecl. As Darwin discovered in his use elimination actual themselves-the present difficulties type of argument, two that of the alternatives and their complete specification. The consequence the kinds if that was proof of notion for Mill's et,olutionary theory had not a in question were species of plants 'and animals, then there were elimiby complete Induction kittds' finite number of sharply distinguishable" but theory' his "prove" not Darwin did rlrtion \'vasimpossible. Not only be forever would proof a such also, given evolution by gradual variation, 6B true, it is not. Empiricists and "idealists," while not equally opposed to the concept of species evolving, were stili both opposed. Evolution by random variation and natural selection conflicted with teleology. Any evolution at all, regardless of the mechanism, as long as it is graduai, conflicted with the essentialist notion of natural kinds-and on the necessityof such natural kinds, empiricists and "idealists" were in agreement. The doctrine of the existence of static, immutable natural kinds underlay ail of the prevrously discussedtopics-inductive proof, occult qualities, and teleology-and evolutionary theory struch a strong blow against this doctrine. One n-right expect Wheweil to argue for the existence of natural kinds, since his metaphysics depended on it. In writing his History Whewell was happy to discover that the most eminent physiologists of his day believed that indefinite divergence from original type was impossible. "Species haae a real existence in nature, and a transition from one to another does not exist."l The impossibility of evolution-or transmutation, as it was usually called-was not a generalization from experience for Whewell but a necessary prerequisite for knowledge. "Our persuasion that there must needs be characteristic marks by which things can be defined in words, is founded on the assumption of the necessarypossibility of reasoning."2 In Whewell's view, if evolutionary theory were true, hnowledge was impossible-not a small drawback to the theory. Peirce (1877) recognized that the "Darwinian controversy is, in large part, a question of logic" and Dewey (1910) tliat "the real significance of Darwinian evolution was to introduce a new 'mode of thinking,' and thus to transform the 'logic of knowledge'." Contrary to Ellegärd's belief, the empiricist philosophies of Herschel and Mill both depended upon tlie existenceof discrete natural kinds. Mill dis. tinguished between two types of uniformities in nature: those of succession in time and those of coexistence. The former were expressed in causal laws, the latter in definitions. Mill's four (sometimesfive) methods of induction were designed to discover succession of kinds of events in time, on the assumption that these kinds had already been discovered.Mill concurred in the essentialist position that natural kinds wele those classeswhich are "distinguished by unknown multitudes of properties and not solely by a few determin2fs 6ns5-\a/hich are partitioned off from one another by 1 . W h e w e l l( 1 8 3 7 ) ,3 : 6 2 6 . 2 . W h e w e l l( 1 8 4 0 ) , 1 : 4 7 6 . irnpossible. reference to Ltill lustinea his belief in the existence of causal laws by inducjustified enumerative by the larv of universal causation. It alone was but coexistence, universal of tion. I{e could fir]d no justification for a law biologists eminent most the he accepteclit anyway on the authority of permitted oi his clay. Mill's belief in a finite number of cliscrete kinds also perIt elimination' hirn to retain his notion of induction by complete The form. in universal nritted him to maintain that all causal laws were a was form in onlv reason for a causal law to be less than universal had kinds natural iailure to distinguish natural kinds accurately' Once immutable beenaccurately distinguished, universality was guaranteed' Thus' Whewell's' to were as central to Mill's philosophy as they were essences induction Whewell was quick to point out that Mill's four methods of the discover' difficult to "take for granted the very thing which is most interpretarerluction of phenomena to formulae'" Induction, in Whewell's were tion, provided these formulae. Whewell believed that observations not think that necessaryfor scientific knowledge. Though Whewell did that they were the lundamental ideas of science were innate, he dicl think progress of the in but facts, as observed out necessary.They might start necessary As truths' necessary as known be to science they would come they could nor just experience, from truths they could not be derivable 3 . M i l l ( 1 8 7 4 ) ,P P '8 0 , 2 0 1 ,4 7 1 . 70 Darwin and His Critics Essences be verified solely by reference to it. Rather they courd be known to be necessary truths only by intuition. The mind superinduces concepts on the facts. These concepts are appropriate if they are clear and distinct .of the permanence of species. (See the comments by CarPenter in his review.) For essentialists,such difEculties and disagreelnentswere only technical problems to be overcome by more careful examination of the data. ,There hnd to be diagnostic characters. For Darwin no such characters (the traditional rationalists' criterion) and if they fit. the facts closely (but considerable latitude is permitted for rei4terpreting the facts to fit tlrc concepts). one of the notable features of whewell's phitosophy of science is that he includes no mechanism for periodic conceptual revorutions. Ile seems to assume that in each area of science there will be one and only one scientific revolution and that in physics that revolution had already occurred. In physics, at least, no future revolutions could occur. A{though whewell's views on science do not preclude a series of conceptual revolu. tions in a particular branch of science, they are certainly biased toward a linear interpretation of scientific progress. In point of fact, whewell hrm" self had an extremely reactionary attitude toward any advances in science after his formative years. A belief in a finite number of discrete kincls of entities underlay both Mill's and Whewell's notions of verification. It also was one of the major factors in the prevalence of occult qualities in science. science deais with classesof entities. on the essentialistview, these classesmust be clistinguish. able by characters which universally covary. Time and again no such set of universally covarying observable characters could be found. Hence, these classeshad to be distinguishable by unobservabre characters. Sometimes this maneuver met with considerable success(e.g., in distinguishing elements by their atomic weight a'd number) . sometimes it did not (e.9., distinguishing life from nonJife by the presenceof a vital force). In reading the scientific and philosophic works of the period, the modern reader often finds himself wondering how essentialismcourd have had the slightest appeal or could have seemed in the least plausible. The answer can be found in its apparent applicability to physical geometry. Here, there was no doubt as to which characters were essential and which were accldental. Maybe all reptiles did not have three-chambered hearts, but all triangles had three sides. Geometric figures were the chief examples of natural kinds in essentialist philosophies from Plato and Aristotle to whewell and Mill. species of plants and animals were the second most popular exarnples. When the diversity of the organic worid was only very poorly known, organic speciesseemed to be as distinct as those of geometry. By the time of Darwin, however, biologists had been forced to recognize that they were not quite so distinct. In fact, the scandalous state of taxonomy was one of the chief arguments used by Darwin against the doctrine 7l ex.istedfor speciesextended in time. Inorganic elements also, on occasion, were cited as examples of natural' kinds, though they ran a very poor third to those of geometry and natural history. (See Jenkin's review.) What must be kept in mind is that for esentialists aLI natural l<inds were equally immutable. Some appreciation of how incredible Darwin's theory must have sounded to his contemporaries can be obtained by realizing that for them one speciesof living creature evolving into another was as impossible as a pentagon evolving into a hexagonor lead into gold. Not only did evolutionary theory seem to PresuPpose spontaneous generation, but also it smacked of alchemy. One can understandDarwin's reticence about Ihaking public his views on the evolu: tion of specieswhen one discovers that half a century later, after scientists had becomeused to the notion of evolution, Frederick Soddy (1877-1956) feared to make public his conviction that transmutation of chemical ele.ments was possible lest the chemists "have his head off." In 19i7, when one chemical eiement was actually transmuted into another, a Darwin ntad his hand in this evolutionary adventure-Darwin's grandson, C. G. Darwin'a Although phiiosophers generally agree that science can have no implications for true metaphysics, theoretical innovations in science from Darwin to Dinstein have necessitated a complete re-evaluzrtion of the notion of natural kinds. The result of this re-evaluation has been the recognition that separate stories must be told for geometric, biological, and chemical species.Philosophers of science contemPorary with Darwin tried to tell one story which would be adequate both for the "cleductive sciences" like and ,seometry and arithmetic and the "inductive sciences" like physics biology. Whewell in the I(antian tradition assimilated the axioms of physics to the axioms of geometry. A1l were a priori. Experience might serve as an impetus to the formation of such ideas, but once conceived,their truth could be known a priori. This position seemedplausible enough {or general spatial irjeas,such as triangles having three sides and parallel lines never meeting, but it began to become somewhat strained when the ideas of causation ancl clesign were included on the list of a priori truths about the empirical world and broke down entirely under such empirical laws as those of Kepler 4 . S c h o n l a n(d1 9 6 8 ) ,p . 1 5 9 . 72 Essences Darwin and Ilis Critics and Newton. Mill, on the other hand, assimilated the axioms of geometry to those of physics, and in this view, he was joined by Herschel. All were inductions from experience. Certain ideas spring from experience, almost i spontaneously, iike very basic notions of space, time, and causation, but l they neverthelesswere empirical claims, whose truth could be decided by ' scientific investigation. Kepler's laws certainly seemed straightforwardly empirical. A body could fulfill all the requirements for being a planet ancl still fail to move in accordance with l(epler's iaws, but the basic axiours of geometry seemed immune to verification or falsification by experiment or observation. The parallel postulate for sure was thought to be a posterion, yet there seemed to be no way to confirm or refute it. Although the current received doctrine in history is that no historical dispute should be elucidated or resolved by contrasting it with the present views on the subject, it seems grossly unfair to leave the reader in the same state of confusion in these natters as that which prevailed in the nineteenth century. The question is whether the axioms of tl-re formal and empirical sciencesare self-evident truths superinduced on the facts by the mind, or truths inductively collected from the facts. For both, the answer is neither. Both sides were mistaken, but the mistal<i was conceptual, not factual. According to the current view, a sharp distinction must be draun between pure, uninterpreted systems, such as. pure geometry, and tlie theories of empirical science, such as physical geometry. All the statements in pure geometry, wl-rether axioms, definitions, or theorems, are tautoiogical and in no sense about physical space. Nor are they truths of reason or of the mind. In Euclidean geometry, parallel lines never meet, and no physical or psychological observation is relevant to this. claim. However, axiornatic systems can be given physical interpretations. For example, the phrase "straight line" in Euclidean geometry can be taken to denote light rays, transforming it into a physical geometry. In such an interpretation, the parallel line postulate is not a priori true. It is false. As an axiom in pure geometry, the parallel line postulate is a priori tr-ue but in no sense about physical space. As an axiom in physical geometry, it is about physical space and false a posteriori. Until this radical distinction was made) no philosopher could hope to understand the relation between the formal and empirical sciences.5 Within empirical science a further distinction must also be made. Species 5. The problem of the relation betweenmathematics.andnatural sciencehas had a long history. Periodically,early thinkers set forth ideas very close to tnose now held on the subject; being ruths of the mind. e.g., Buffon. However, Buffon viewed mathematics as IJ .of inorganic objects differ in several important respects from species of of chemical elements was i.Flants änd animals. Earlier the transmutation ,:eOnrpar.cdto the evolution of species, but the two Processes are very differinto a like quantity of one element quantity ent. Pliysicists change a small number, i..ni another'element. Lead and gold, defined in terms of their atomic were trans- ' i still renrain lead and gold. Even if all the lead in the universe in the lead for be reserved -'. nruted into other elements, a spot would still it rnore, once to form were ti:ni*nsification of eiements. If eventually lead element physical a which ' vould be lead, Pure and simple. The process by .. is generatedand its past history are irrelevant to its identity. 'Ihe situation is quite different with respect to speciesof living creatures. Biologistscommonly maintain that speciesmust be monoPhyletic. Various but the two most prevalent definitionsof "monophyly" have been sr.rggested, definitions are (a) a taxon is monophyletic if it is derived by descent from a single immediately ancestral species; and (b) a taxon is mono' phyletic if it is derived by descent from a single immediately ancestral täxon of its own or lower rank. On interpretation (a) a family is monophyletic only if every speciesincluded in the family is derived from another intpgcies in the family or at most one immediately ancestral speciesnot rluded in the taxon. In interpretation (b) a famll:y is monophyletic only if every speciesincluded in the family is derived from another speciesin the lamily or from one or more species not included in the family, as long as all of these speciesbelong to the same family. In either interpretation species become historical entities. Having the appropriate Past history is necessaryfor a speciessto be the species that it is. For example, if a speciesof dinosaur were to evolve from present-day reptiles which was in every respect, save its phylogenetic history, identical ts an extinct species of reptile, it would still be a new, separate species' This view of species as being monophyletic evolutionary units is the currently clominant view.6 Tl-rere is also a minority view that animal species should be treated like chemical elements defined symPtomatologically,T and at least one philosopher agrees with this position.s Thus, Darwin's theory had two seemingly contrary implications for the relation of biology to physics. Its naturalism brought biology and physics into closer accord, but its apparent reliance on historical concepts tended to drive the two apart again. 6 . S e eS i m p s o n( 1 9 6 1 )a n d M a y r ( 1 9 6 9 ) . 7. Sokaa l n d S n e a t h( 1 9 6 3 ) . B. Smart(1963). 75 Darwin and l{is Critics Essences Darwin dismissedtheological explanations of the origin of speciesbecause they were not properly scientific. Ile also dismissed explanations in terms of "plans," divine or otherwise. They, too, were empty verbiage. Explana- .ntre not so much refuted by Darwin as discounted. Similarly, the theologisal and metaphysical objections to evolutionary theory gradually subsided, 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 over a century before Darwin, especially in the writings of ideal morphologists like Goethe, Cuvier, Owen, and Agassiz. As long as one believed in God, and these plans could be interpreted literally as thoughts in the mind of the creator, then such explanations had some explanatory force, but if reference to God is left out of the explanatory picture, then all that is left are the plans. Rather than being explanations, the existence of such "plans" calls for explanation. In England, at least, Darwin's aversion to scientific explanations in terms of explicit reference to God and conformity to plan was shared by a growing number of scientists.For example, Edward Forbes,e in 1854, published an explanation of the distribution of living creatures in geological time in terms of polarity, "a manifestation of force of development at opposite poles of an ideal sphere." Forbes divided geological time into two periods-the Neozoic and Paleozoic.The distribution of generic types then {ormed a figure eight with its constriction during the Triassic and Permian epochs. Although Forbes argued that this distribution occurred in time, the explanatory ideal plan was atemporal. To put Darwin's reaction to Forbes's explanation simply, it made him sick. trither it rvas nothing rnore than a description of the distribution of generic types in time or else it was lihe magnetism turning a table.1oDarwin could not see how references to ideal plans could explain anything. To say that the hand of a man or a monkey, the foot of a horse, the flipper of a seal, the wing of a bat, and so forth, have all been formed on the same ideal plan "is no scientific explanation."rl One of the purposes of evolutionary theory was to provide a naturalistic explanation for such homologies.l2 Modern readers of the Origin of Species tend to grow impatient with Darwin for going to such lengths to argue against sp3cial creation and divine plans. They are no longer considered even viable candidates for scientific explanations. The decision was not so clearcut in Darwin's day, Many philosophers and some scientistsstill looked upon miracles and ideas in the mind of the creator as acceptable elements in a scientific explanation, though most scientists were loath to discuss the issue. These "explanations" matterecl was listening any more. The change can be seen in the diserence between the aggressive confidence of Agassiz's first review of i.thr Origln ot' Speciesin 1860 and the petulant timidity of his final comments in 1874. Even in his original review of the Origin, Agassiz acknowledged ihat lome naturalists looked upon his idea of creation by God's mental exertion as a kind of bigotry and his holding the view a sign of non üafil)or ntentis.Fourteen years later he hardly dared mention his pet theory of creation by repeated acts of divine cognition. Owen went so far as to assert that the leading naturalists of the day, referred to by Darwin as Sp€cial creationists, had neuer mai1.tained the view that species n'ere $peciallycreated by divine action. Rather, he along with the other so-called rpecial creationistshad always maintaintjd that some unknown law governed rhe introduction and extinction of species.Lyell, to the contrary, had the candor to admit that he "formerly advocated the doctrine that species t'ere primordial creations, and not derivation."t3 FTe differed from the catastlophistsonly in his belief that specieswere creatöd and extinguished serially,ratl-rerthan in wholesalelots. Naturalistic explanations,had become the order of the day. The authors included in this anthology by and large agreed that scientific theories were to be judged only by scientific standards. Even the philosopher primed b.vAgassizfor his review of the Origin, Francis Bowen, admitted "all that has been claimed for the proper independenceof true physical science,-that its conclusions are to be tested by their own evidence, and not by their agreement or want of agreement with the teachings of Scripture, with reeeiveddoctrine in theology or philosophy, or with any foreign standard whatsoever."laLike Newton's hypothesis non fingo, this proclamation was easierto declare than to implement becausethe boundaries between science, philosphy, and theology began to blur when one approached the problem of man's menta.l powers and morai nature. These faculties had always beentl.reprovinces of philosophy and theology. While perusing the following reviervs,the modern reader may be puzzled by the disproportionate attention 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,July2, 1854, AIo1'e LetLcrs(1903) , l:?7. l l . D a r w i n ( 1 8 7 1, )p p . 3 l - 3 2 . I2, Scc llopkins, Mivart, and \Arrigbt revicws in this volume o f - F o r b c s ' sp r i r r c i i r l e o f p o l a r i t y . '..bpinion 13.Lyell (187g), p.469; seealso the reviewsof Hooker,Carpenter,Wollaston, fol additional opiuions and Fawcett in this volume. 14. Bowen (1860), p. 476' I : 76 Darwin and His Critics Essences taking his first steps toward the explanation of man's higher faculties. I-Iis intentions were not lost on his reviewers. The conclusions ol true physical science were to be judged only by scientific standards, but Darwin was trespassing on the property of philosophy and theology and deserved to be criticized by their standards, and this authors like Sedgwick and Bowen proceeded to do. In doing so, they were not intruding on the proper domain of science. Rather, in Bowen's words, the "intrusion, if. any, comes from the other side. It is now the naturalist, the pure physicist, who, quitting but they occur rarely. Given what we know of genetics and population biology, gradual evolution is the rule. Huxley's suggestion has been taken up periodically by scientists (e.g., Goldschmidt ärrd Schindewolf). From a pulely scientific point of view there is no a priori reason {or preferring one tylle of evolution over the other. From a metaphysical point of view, therc is. Speciation by saitation would permit the retention of the discrete-' his own territory, but, as he professes,still relying exclusively on physical evidence, seeksto build up metaphysical conclusions."l5 Even after the boundary between philosophy and science was redrawn to distinguish between psychology and epistemology, the adjustments rn philosophy necessitatedby evolutionary theory were of the most fundamental hind. Either one of the chief examples of natural kinds had to be dismissed as not actually being natural kinds, or else the notion of natural kind had to be reworked. Some philosophers chose the forrner alternativc and retreated to geometry. Bos bos was not properly a natural kind. Equilateral triangles were. Relativity theory drove the adherents of natural kinds out of their last sanctuary. Some philosophers took the second alternative and tried to produce a metaphysics which did not depend on the essentialist notion of natural kinds. The extreme difficulty of this undertaking can be seen in the development of philosophy during the last fifty years.t6 Later criticisms of evolutionary theory tended to be directed at Darwin's mechanisms---chance variation and natural selection. Perhaps species evolved and a naturalistic mechanism is called for, but Darwin's explanation was inadequate. The two modifications of evolutionary .theory most frequently suggested were the substitution of evolution by saltation for Darwinian gradual evolution and the addition of a force or principle internal to organisms to direct them in their evolutionary development. The former served to salvage the discreteness of natural kinds, the latter to save teleology. Even Darwin's strongest supporters took great pride in keeping one toe dry. Huxley, for example, thought Darwin had loaded himself "with an unnecessary difficulty in adopting Natura non facit saltum so unreservedly."rz By and large, Darwin was right. There are genetic mechanisms which result in new species' evolving in a single generation (polyploidy), 1 5 .I b i d . , p . 4 4 7 . . 16.D. L. l-lull (1974) 17.L. Huxley (1902) , p. I89. 77 nessof natural kinds, a tenet central to essentialism. Gray, Wallace, and Lyell all argued for the inclusion of some vestige of teleology in evolutionary theory. On this score, they were joined by a host of other scientists,including Owen and Mivart. Mivart, for instance, reasonedthat just as there was a principle internal to an individual organism rvhich determined its regular embryological development, there must also be a similar principle to determine the evolutionary development of species' By reasoning in this manner, these scientistswere returning to something like the Aristotelian notion of imrnahent teleology. In this case, however, thc cnd was not a cyclical returning to the same type but a progression from one type to another. Darwin could find no evidence of such a directing internal influence and steadfastly refused to admit it. Once again, Darwin seemsto have been right. We now know why organisms go through their regular cycles of development-the information coded in their DNA. This infonnation has been built up through eons of natural selection. No hint of a mechanism by which the future development of a species may also be incorporated into this code has been discovered. The truly amazing feature of Darwin's intellect was the frequency with which he was able to "guess" correctly, even though he iacked the requisite data and anything like an adequate theory governing the phenomena. Modern evolutionary theory is closer to the original Darwinian formulation today than it has ever been.18 which are almostdiamerically lB. PeterVorzimmer (1970) comesto conclusions opposed to those expressedin this Introduction with re5Jardto Darwin's adherence to gradual evolution and innate directive forces. Vorzimmer thinks that Mivart's 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 cve of his retirement" (p. 250). See the discussion of Mivart's review of The Descent of Man (1871.) in this volume for further examination of vorzirhmer's analysisof the situation. Douglasf. Futuyma StateUniversityof NewYorkat StonyBrook Evolution : -, .. '! $ "'ii e ffiLÄT ,, lii$, ü*"')l:1$äffiffiÄ ,;f**,* o; =illd;** "üHä-11Tffi.sffi :;,= ääHff H: "' ff,fbtr -'-,, .*:.-__* * _ä Chapter19 (Evolutionof Genesand Genomes) by ScottV.Edwards,HarvardlJniversity Chapter20 (Evolutionand Development) by Iohn R. True,StateUniversityof NewYork at StonyBrook Übersetzungvon AndreasHeld Spektrum x-/l AxlDBmscHEn vEtLAo I Zuschriften und Kritik an: ElsevierGmbH, SpektrumAkademischer Verlag,Merlet Behncke-Braunbeck, Slevogtstraße 3-5, 69126Heidelberg; Mail: [email protected] Autor: Douglas J. Futuyma Lehn^rmuleh Titel der Originalausgabe: Evolution Amerikanische Originalausgabe2005 bei SinauerAssociates,Inc.,23 Plumtree Road, Sunderland,MA 01375,USA Copyright @ 2005 by SinauerAssociates,Inc.. A1l rights reserved. I S B N : 0 - 8 7 8 9 3 -18 7 - 2 www.slnauer.com 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 ' E. Mayr courtesy of Harvard News Service and E. Mayr '-. G. L. Stebbins,G. G. Simpson, and Th. Dobzhansky courtesy of G. L. Stebbins ,*--lM. Kimura courtesy of William Provine " 'J Übersetzer Andreas Held Wichtiger Hinweis für den Benutzer Der Verlag und der Autor haben alle Sorgfalt walten lassen,um vo11ständigeund akkurate Informationen in diesem Buch zu publizieren. Der Verlag übernimmt weder Garantie noch die juristische Verantwortung oder irgendeine Haftung für die Nutzung dieser Informationen, für deren Wirtschaftlichkeit oder fehlerfreie Funktion für einen bestimmten Zweck. 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Planung und Lektorat: Merlet Behncke-Braunbeck, Imme Techentin-Bauer Herstellung: Katrin Frohberg Umschlaggestaltung:wsp designWerbeagenturGmbH, Heidelberg Titelfotografi e: Andreas Held LayoutiGestaitung: TypoDesign Hecker GmbH, Leimen Satz: Mitterweger & Partner, Plankstadt Druck und Bindung: Grafos s.a.,Barcelona Prinled in Spain ISBN 978-3-82741 - 816-6 Aktuelle Informationen finden Sie im Internet unter www.elsevier.de und wwu'.elsevier.com Inhaltsüberblick Kapitell ' E v o l u t i o n s b i o l o1g i e s :l a s s i f i k a tui onndP h y l o g e n1i e7 e sL e b e n K Kapitel2:, D e rS t a m m b a udm 43 Kapitel3: Evolutionsmuster 67 in denFossilbelegen Kapitel4,' Evolution aufderErde91 desLebens Kapitel5" EineGeschichte Kapitel1,;,D i eG e o g r a p hdi e rE v o l u t i o1n1 7 139 derBiodiversität KapitelT, DieEvolution 161 Variabilität dergenetischen S DieEntstehung Kapitel -, Kaprtelg ' V a r i a b i l i t ä1 t8 9 225 nachdemZufallsprinzip Drift:Evolution Kapitella'. Genetische 247 undAnpassung Selektion KapitellI , Natürliche : 269 Selektion Theorie dernatürlichen Kapitel12 Diegenetische phänotypischer 297 Merkmale Kapitell:J" DieEvolution 325 Kapitel14 ' KonfliktundKooperation Kuoitel15 ', Arten353 g7 9 Kapitel16 A r t b i l d u n 3 a05 Fortpflanzungserfolg KapitellT Fitness: vonWechselbeziehungen DieEvolution KapitellB Coevolution: Arten429 zwischen 449 Kapttellg DieEvolution vonGenenundGenomen Kapitel20 Evolution 473 undEntwicklung Kapitel2t Makroevolution: derArtebene501 Evolution oberhalb 523 Kapitelz2 Evolutionswissenschaft, undGesellschaft Kreationismus 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 man, fascinated with all of biology, creative in devising hypotheses and in bringing evidence 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. rvissbegierig Erstelien n'sEvolutionaryTheory Darvvi 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 interruption, from one or a few original forms of life (Figure 1.3B).Speciesthat diverged from but accumulateddifferencesover gleat SPans a common atcestor were at firSt very simila-5, 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' The second theme of TfteOrigin of Speciesis Darwin's iheory of the causal agents of evolutionary change.This was his theory of natural selection:"if variations useful to äny oreanicbeing 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: don, or the survival of the fittest, I have called natural selection."This theory is a vaRlaTransfornational evolution Generation I Abstammuirg Ursachen Nachkommer / Erhaltrurg, I(onservierung .,,Variationstheorie" Generation 3 Generation 2 Reproductive age (RA) Birth (B) Unterbrechung BR,\B RA O--+C O+O O +O OO O +O O +O Time+ Vuiational evolution Reproductive age (RA) Birth (B) o o @ + Generation3 Generation 2 Generation I RAB B O------*O +C-------O tle + O ------ + ,--@ q -::l--> 6 + O 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,taly representedearlieiand later in their liver]Th" i.tdiridrr^ls in the leit column [Spalte] in each ge-neration are the olfspring of thosein the right column of the preceding Ivoihärgehen.tlgeneration' 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 . rt l:t:,',t::! liffutent forms at ihe beginning of the history are not transformed, but instead diffär survlval and reproductive rate-flrortp;lanzungsrate], so that their proportions change from one generaHonto änother. , C H A P T E R1 ,,Transforrnationstheorie" noN+L of change, diffeling profoundly fiom Lamarck's TRANSFORMATTONAL rFrF^D,, T.rEoBy 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 erstellte Craclualisrnus Spt'tirrge/ Saltationen Zrryisclrenstnfen ii r1 anPassel-r Abkörnrnlinse adaptiv Lebensgewohnherten 7 I(onknlrenzdruck D i v c r g e r r zA, r rp a s s u r r g snut e r schiede. Lücke vorherrschend / Vererbrrrrgquantitativer Melkmale / abnehmen Vermisclrer.r partikuläre Verelbrurg überdauerrr 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 Darwin 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 diverged from common ancestors and that all of life could be portrayed as one grear family tree. 3. Qls!'tglhuis Darwin's proposition that the differences between even radically different organisms have evolved incrementally, by srnall steps through intermediate forms. The alter.ative hypothesis is that large diffe'ences evolve by leaps, or sALrAttoNs, r,t'ithout intermediates. 4. Populational clmnge is Darwin's thesis that evolution occurs by changes in the proportions of individuals within a population that have different inherited charaCteristics (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 account of evolutionary change by transformation of individuals. 5. Natural selection was Darwin's brilliant hypothesis, independently conceived by 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 result in the evolution o{ adaptations, features that appear "desigrred,, to fit organisms to their environment. The concept of nafural selection revolutionized nöt only biology, but Western thought as a whole. Darwin proposed that the various descendants of a common ancestor evolve different features beiauie they are adapfive .-a"t atff"t'"t-rt "conditions of life"-different habitats or habits. Moleovel, the pressure of competition favors the use of different foods or habitats 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 time, there is no evident limit to the amount of diversence that can occur_ 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 prgvail!4g belief in BLENpTNcrNHERrrANcE,variation should decrease, not incre4se. Because 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 of paint. Blending white and black paints produces gray, but mixing fwo gray pairts doesn't yield black ol white: variation decreases. Darwin never knew that Gregor Mendel had irr fact solved the problem in a paper published in 1865. Mendel's theorli of pen:rrculars INHERITANCE proposed that inheritance is based not on blending fluids, but on particles that pass unaltered from genelation to generation-so that variation can pers:is.!.The co.tcept of "mutation" in such particles (later called genes) developed only after 1900 and was not clarified until considerably later. EvolutionaryTheoriesafter Darwin folgte Paläontologre / r'erg;leicher-rde Morpirologie Fossilbelege, Fossilfunde Altlrough Theorigin of speciesraised enormouscontroversy,by the 1870smost scientists acceptedthe historical reality of evolution by common descent.There ensued,in the late nineteenth and early twentieth centuries,a "golden age" of p4lepqlqlegy, comparative morphology, and comparativeembryology,during which a great deai of information on evolution in the fossil record and on relationshipsamong organismswas amassed.But this consensusdid not extend to Darlsin's theorv of the causeof evolu- adaptation Anpassung, Adaptation / environment Umwelt E V O L U T I O N A RB YI O L O G Y tion, natural selection.For about 60 years after the publication of TheOrigin of Species, ali but a few faithful Darwinians rejectednatural selection,and numerous theorieswere proposedin its stead.Thesetheoriesincluded neo-Lamarckiaryorthogenetic,and mu, iationist theories(Bowler 1989). Nro-LevlqncrrsM [Neolamarckismus] includes severaltheories based on the old idea of inheritance of modifications acquired during an organism's lifetime. Such modifications might have been due, for example,to the direct effect of the environment on development (as in plants that develop thicker leaves [Blätter] if grown in a ho! dry environment). 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.Exiensive subsequentresearchhas 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 biologistswho "discovered" Mendel's neglected paper in 1900,and by Thomas Hunt Morgan,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 sudden, drastic changesthat reorganize the whole genome. Although most such reorganizationswould be deleterious [nachteilig], a few "hopeful monsters" would be the progenitors [Vor1äufer'.] of new groups. TheEvolutionary Synthesi s Theseanti-Darwirrianideas were refuted [widerlegt, angefochten]in the 1930sand 1940s by_the evolutionary synthesis or modern syntheiis, foiged from [geformt aus] the conki-butionsof geneticists,systematists,and paleontologistswho reconciled [abglicheryab, stimmtenl Danrrin's theory with the facts of genetics(Mayr and provine 1980;smocovitis 1996).RonaldA. Fisherand JohnB. s. Haidane in England and sewall wright in the unitedstates.developeda mathematicaltheory of population genetics Ipop*ulationsgenetikl,which showed that mutation and nafural seleciion togethercauseidaptive evolution: mutation is not an alternative to natural selectiorybutls rather its raw material. tqov of geneticvariation and changein natural populations was pioneeredin RusIh: siaby sergeichetverikov and continueä by Theodosius Dobzhansky,who moved from Russiato the united states.ln his influential book Geneticsand the origin of species(1937), conveyed the ideas of the population genericiststo other*bioiogists,thus in?-*l*tly ttuT:*t their appreciationof the ge.,eti. busis of ävolution. *.uio. contributors to the synthesisincluded the zoologists Ernst Mayr, in Sys,_Y:1". O.rigittof Species (1942),andBernhardRensch,in EuorutionAboae'theSpecies iT,:i::::!,the tne b-otanistG. Ledyard Stebbins,inVariation and Eaobttionin plants (1950); :"j',Lt^"rJ, lil $-eut"ontologistGeorgeGaylordSimpson,tnTempoandModein Euolution \1944) l\..rchLntccr.J, Th'eMajor Fe'attLres of Eaolution(1953).Theseauthorsarlll^t'l^t_T*ttor öqcu Persuasivelythat mutation, recombination, nätural selection,and other processes sEWALLWRIGHT 9 lo C H A P T E R1 ERNSTMAYR G. LEDYARDSTEBBINS, GEORGEGAYLORDSIMPSON,AND THEODOSIUS DOEZHAN5KY openttnsToithin species (which Dobzhansky termed microevolution) account for the origin of newspecies atxdfor themajor,Ionglermt'eaturesof eaolution(termed macroevolution). stichhaltig Genotyp zurückzufuhren Cene behaiten Merkmale polvgene Vererbtmg Allele verstärkt / Rekombination Genorte, Genloci (Singular: Genlocus) bedingt, hat zur Folge Frequenzen, Häufigkeiten '-'_-*"ö*-'ö Vpr',lränor rno zufällig genetischeDrift, Gendrift macroevolution Makroevolution Fundamentalprinciplesof evolution The principal claims of the evolutionary synthesis are the foundations of modern evolutionary biology. Although sorne of these principles have been extended, clarified, or modified since the 1940s,most evolutionary biologists today acceptthem as fundamenta1ly valid. These,thery are the furdamental principles of evolution, to be discussedat length throughout this book. 1. Thephenotype(observedcharacteristic)is dffirent ftom theK!\fupg(the set of genes in an individual's DNA); phenofypic differencesamong individual organisms may be due partly to genetic differencesand partly to direct effectsof the environment. 2. Environmental effectson an individual's phenotype do not affect the genespassed on to its offspring. In other words, acquiredcharacteristics arenot inherited. 3. Hereditary variations are based on particles-genes-that retain their identity as they passthroughthegenerations; theydo not blendwith other genes.This is true of both discretely varying traits (e.g.,brown vs. blue eyes)and continuously varying haits (e.g.,body size, intensity of pigmentation). Genetic variation in continuously varying traits is based on severalor many discrete,particulate genes,each of which affects the trait slightly ("polygenic inheritance"). 4. Genesmutate, usually at a fairly low rate, to equally stable altemative forms, known as alleles.The phenotypic effect of such mutations can range from undetectableto very great.The variation that arisesby mutation is amplified by recombination among allelesat different loci. 5. Eaolutionarychangeis a populationalprocess: it entails,in its most basic form, a changein the relafive abundances(proportions or .frequencies) of individual organisms with different genotypes (hence, ofteru with different phenotypes) within a population. One genotype may gradualiy replaceother genofypesover the course of generations.Replacementmay 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 population can occur by either of two principal processes:random fluctuations in proportions (geneticdrift), or noruandom changesdue to the superior survival and/or reproduction of some genotypescompared with others (i.e.,natural selection). Natural selectionand rarrdom genetjc drift can operate simultaneously. / microevolution Mikroevolution ;:: t $ E V O L U T I O N A RB YI O L O G Y 7. Even a slight intensity of natural selectioncan (under certain circumstances)bring about substantial evolutionary changein a realistic amount of time. Natural selection as well as for the earliest cannccountfor bothslight andgreatdffirencesamongspecies, 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 affect the sametrait, give rise to new phenotyPes. 9. Natural populations are geneticallyvariable, and so can often evolve rapidly when environmentalconditions 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 population. Speciesare not defined simply by phenotypic differences.Rather,different speciesrepresentdistinct "gene pools"; that is, speciesare grouPs of interbreeding oi potentially interbreeding individuals that do not exchangegeneswith other such glouPs. 14. Speciationis the origin of two or more speciesfrom a single corrunon ancestor.Speciation usually occursby the geneticdifferentiation of geographically segregated populations.Becauseof the geographic segregation,interbreeding does not prevent incipient geneticdifferencesfrom developing. 15. Among living organisms,there are many gradations in phenotypic characteristics among speciesassignedto the samegenus,to different genera,and to different 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." 16. The fossil record includesmany gapsamong quite different kinds of organisms.Such gapsmay be explainedby the incompletenessof the fossil record.But the fossil recordalsoincludes examplesof gradationsfrom apparently ancestralorganismsto quite different descendants.Thesedata support the hypothesisthat the evolution of large differencespISg994Cl4Ie!qC!tA!y. Hence the principles tha! explain the evolution of populationsand speciesmay be exhapolatedto the evolution of higher tara. Allelfrequenz sich unteleinander kreuzend Genpools Artbildung, Speziation Differenzierung / getrennt einsetzend,begimend. Gattung Entstehung schreitet stufenweise voran _'"-_'ö-_--__'-hnchoererhnpf EvolutionaryBiology sincethe Synthesis Sincethe evolutionary synthesis,a great deal of researchhas elaboratedand testedits basic principles.Beginning in the 1950sand accelerating [sich beschleunigend] since, advancesin geneticsand molecular biology have virfually revolutionized the study of evol"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 phylogenetrchistory 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 characteristicssuch as life span, ecologiial dishas been renewed byfrovoca$b1dory and social behävior. The study of *uo*"of"Uon ., , I":t^l*:Oretations of the fossil record und by ,,"* methods for studying phytogeneticreVerwandischaftsbeziehungen]. ai methods illl-Thpt Istamnresgeschichtliche mo." sophisticatedand available,virtually new"fieids of-ät"."tui evolutionary study . HLl1":"le navedeveloPed. Ambng thesefields is Hlor-scuranEvoLUTroN ImolekulareEvolution] MOTOO KIMURA 11 12 CHAPTER 1 Nerr tralther:rie der molektrlaren Evoh-rtion, Mutationstlreone evoluti or1äre Entwicl<lun gsbiologie einschränken evolutiouäre Genomik ganze Genorne (analyses of the processesand history of change in genes), in which the xsurnaL rHeoo,, oF MoLEctr-AR EvoLUTIoNhas been particularly important. This hypoihesis, develope4 qspecially by Motoo Kimura (1924-7994), holds that most of the evolution of Di\A s;_ quences occurs by genetic drift rather than by natural selection. Ev!:r-urro_Nanyorv.rLoi_ MENTALBrolqcy is an exciting field devoted to understanding how developmental processes both evolr'e and constrain evolution. It is closell'tied to developmentuiliotog;; one of the most rapidly moving fields of biology today. EvoLurroNeRv crNorr4rcs.q6ncerned lt ith variation and evolution in multiple genes or even entire genomes, is bei.o born. The advances in these fields, though" are coÄplement"a Uy ;;.f; "iffiireGrd, discoveries, and new ideas about long-standing topics in evolutionary biology, such as the evolution of adaptations and of new species. This is an exciting time to löarn about evolution-or to be an evolutionarv biolosist. Philosophicallssues Foleen,Ausrvirkurrgen lehnte alr endlos Stasis Erdbeben Zweck überflilsr1t r.ermehren ft'uchtbar; produktir, / r'erunsi chernd Wasserstoffbrirckenbindungen 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 radicaily, given enough time. Thus he reiccled the essentialism that western philosophy had inherited from Plato and Aristotle and put variation in its place. Darwin also helpeä to replace a static conception of the n'orld-one virtually identical to the Creator's perfect creation-with a world of ceasglesschange. It was Darwin who extended to living things, 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, purposeless natural selection provided a revoiutionary new kind of answer to almost all questions that begin with "Why?" Before Darwiry both philosophers and people in general 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 flowers?" or "Why are there apple trees?"-or diseases, or eartlrquakes-were answered by imagining the possible puIpgEC that God could have had in creating them.'Ihis kind of 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 evolutionary biologists, the flower of a magnolia h as a function, but not a purpose. it was not designed in order to pgqp_Agatethe species, much iess to delight us with its beauty, but instead came into existence because magnolias with brightly colored flowers reproduced more p1q1if4e1b than magnolias r.rrith less bdghtiy colored flowers. The unsettling implication of this purely material explanation is that, except in the case of human behavior, 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 nor chemists the purpose of hydrogen bonds. The concept of purpose plays no part in scientific explanation. Ethics,Religion,and Evolution Handehr u'örtliclr ln the world of science, the reality of evolution has not been in doubt for more than a hundred 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, 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 with a literql reading of the creation stories in the Bible's Book of Genesis, as it is incompatible 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) :1,: i;l 1;.,l {i.. ,it t::: 't, i{ \i r 524 C H A P T E R2 2 TheEvidencefor 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 studies that might be cited for each particular line of evidence. In this section, we will simply review the sources of evidence for evolution and refer back to earlier chapters for detailed examples. The fossil record i 1r:-rri'"]"1-" i_ jrt ii_t.til.:.:a:rijtt i! Jli'iI \ |LI I) Ll: The fogsil rqqarci is extremely incomplete, for reasons that geologists understand well (see 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 provides 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 evolution: 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 expected, 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 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, algae precede vascular plants. ferns and "gyll4Alpglalq" precede flowering plants. Phylogenetic and comparative studies , : , . . i r i . l ' , 1 i i ,i r . \ , . ; r , . r : . i i Although many uncertainties about pfrylogsletLqfcleüS4üpg persist (e.g., the blanch; . , I ' . I i r r i - . , , i . t L ; i ; r ' , r i , r i i I , , 4.!g_aldcl of the major groups of birds), phylogenies that are well supported by one class rl,.rr \ r'l /,.\ i:.]tilll '..'l'- i..i.rl.'r.: |ii, | | :i:::,--ttt-r:r ". t:. li it:ti,.:tl il llir'l;t rl l r'- lit'i::i1l,r:rr| .i'; -ifrirr.'i J'i, lr !_,, rir\:,ll.il lrr.irlr, lr of charactersusually match the relationships implied by other evidence quite well (see 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 independent (the molecular phylogenies are often based on sequencesthat have no bioIogical function), so their correspondencejustifies confidence that the relalionships are real: that the lirya&eq form glogplrylejiSg{o,Up! and have indeed descended frorn common 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 machinery of nqelel! 4c1dre+liealis4, the mechanisms of transcription and translation, 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 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. $+cteaaliltc have shown that the differences among rc]4lcd species often form gracual series, ranging from slight differences to great diffärences with stepwise intermediates (e.g.,Figure 3.21).Such intermediates often make it difficult to establisl-rclear-cut families 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 E V O L U T I O N A RSYC I E N C EC, R E A T I O N I S M AN , D SOCIETY studies have also demonstrated the common origiry or hSglo_bry, of characteristics that may differ greatly among taxa-the most familiar examples being the radically different forms of limbs among tetrapod vertebrates. Homology of stmctures is often more evident in early developmental stages than in adult organisms, and contemporary dgyelqg mental biology demonstrates that Hox gg4gq and other developmental mechanisms are shared among animal phlzla that diverged from common ancestors a billion or more years ago (see Chapter 20). 529 Hrtmolirqie Enth'icl<lr.: ngsb iolosle Hor-Cenc I-ierstämme Genes and genomes The revolution in molecular biology and genomics is yielding data about evolution on a Iarger scale than ever before. These data increasingly show the extraordinary commonal{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 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 of "selfish" transposable elements that generally provide no advantage to the organism. These features are readily understandable under evolutionary theory, but would hardly be expected of an intelligenf omnipotent designer. Molecular evolutionary analyses have shown in great detail how new genes arise by processes such as unequal crossing over, and how duplicate ge4Cqdiverge in functiory increasing the genetic repertoire (see Chapter 19). Some DNA polymorphisms are shared between species,so that, for example, some maior histocompatibi of humans are more similar and more closely related to chimpanzee sequencesthan to other human sequences(see Figure 12.238).What more striking evidence of common ancestry could there be? Among the many other ways in which molecular studies affirm the reality of evolution, consider just one more: molecular clocks. They are far from perfectly accurate, but sequence differences between species nevertheless are roughly correlated with the time since common ancestry, judged from other evidence such as biogeography or the fossil record (see Chapters 2'and 4). The sequence differences do not simply encode the phg4q 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. Centrnrik Ccmeirrsamkcit g e m e i n s . r n r eA b s t a m n rL rn g nichtcoclierenrlc i'ser-r rlogene / S a t e l l i t e n - D \ A / I ' a i l l e. , , e e o i s t i s c h e " t r a n s l r o n i e r b a r cE l c m e n l e i ;r1lrnäcl'rtig u n g l e i c h e sC r o s s i n g - o v e r d r,rpiizii..rte Oc.ne Polvrnorphismen H a u p t - F l i s t o k o r n p at i b i l i t ä t s S t - q u tn z en m L r l e k u l . r r eU h l r - . n '.1,-i.,rh,'ri.,-1.,. I i,r f.'r* h i,., 1 Biogeography We noted in Chapter 6 that the geographic distributions of organisms provided Darwin 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 phylogeny of Hawaiian species matches the sequenceby which the islands came into existence. We saw that diverse ecological niches in a region are typically filled not by the same taxa that occupy similar niches in other parts of the world, but by different monophylg!4€Iqqp! that have undergone independent adapl!vg_I44i41iq4 (such as the anoles of the Greater AnLilles). We sary as did Darwin, that an isolated region such as an island is not populated by all the kinds of organisms that could thrive there, as we might suppose a thoughtful designer could arrange. Instead, whole groups are commordy missing, and human-introduced species often come to dominate. VerLrreitrrngen Auflirsr-rng irkologischt Niscl-ren r-nouophr')eti schc.Cn-rpp.erl a d a p t r rc R . r c t a t i o u GnrßeAntillen F a i l u r e so f t h e a r g u m e n t f r o m d e s i g n Since God cannot be known directly, theologians such as Thomas Aqqtleq have long attempted to infer His characteristics from His works. Theologians have argued, for instance, that order in the universe, such as the predictable movement of celestial bodies, 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 : t7 Thomas von Acltrin , Himnrelskörper- 53() C H A P T E R2 2 tvohh'oIIeurl Segen g n a r l e n l o sa u s g e l a c l - r t Antrieb Desigr.rargurlen t Falce, Cegenstancl rles Spottes Eventualitäten rutli urc.ntärc(r'erkii urr-nerte)Organe Bt'cken / Obc.rschenkelknocher.t venvachscne Fliigeldecken / funkIior.rs]oseStatrbblätter ocler Stempel r g e t r r . l r n t e e s c h l t c h t l i c h/ ' . r r r' I r r r _i i r r5r ' l -i'r ' l rz r r i l l r i r ' , ' r Z t r . t a n . l cktotherur, u,echseln,alm Aortenbiigt-n / Enc'lothelme,Gleich\\'.1rme pentacl.rktvleliiinffingriee) Extre.mität gelenkig endosymbionlisch / I'}hotosynthese zr:fällig Inbegriff Siclrelzellanämie auf Kosten homozVgot heterozvroter Träger in Ern ägur.rgzu ziehen erhalten Umstände similarly be infefred that God is a rationaf intelligent designer who, furthermore, is beneficent: 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 position 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 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 evident in organisms implies a designer of life. This "argument from design" has been renewed in the "intelligent design" version of creationism, and it is apparently the most frequently cited reason people give for believing in God (Pigliucci 2002). Of course, Darwin made this particular theological argument passd by providing a naiural mechanism of design: natural selection. Moreoveq, Darwin and subsequent evolutionary biologists have described innumelable examples of biological phenomena that are hard to reconcile with beneficent intelligent design. just as Voltaire showed (in Candide) that cruelties and disasters make a mockery of the idea that this is "the best of all possible worlds," biology has shown that organisms have imperfections and anomalies 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, incompetent, or handicapped designer? Only evolutionary history can explain vestigial organs-the rudiments of once-functional features, such as the tiny, useless pelvis and femur of whales, the reduced wings under the fused wing covers of some flightless beetles, and the nonfunctional stamens or pistils of plants that have evolved separate-sexed flowers from an ancestral hermaphroditic condition. Likewise, only history can explain why the genome is full of "fossil" genes: pseudogenes that have lost their function. Only the contingencies of history can explain the arbitrary nature of some adaptations. For instance, whereas ectothermic ("coldblooded") tetrapods have two aortic arches, "warm-blooded" endotherms have only one. 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 pain or wisdom teeth can testify. Or-rcethe pentadactyl limb became developmentally 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 flexibiiity 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 harboring 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 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 not) and a process that is the very epitome of waste and seeming cruelty (natural selection, which requires that great numbers of organisms fail to survive or reproduce). It would be hard to imagine a crueler instance of nafural seiection than sickle-ceil anemia, whereby part of the human population is protected against malaria at the expenqgof hundreds of thousands of other people, who are condemned to die because they are homozygous for a gene that happens to be worse for the malarial parasite than for heterozYgous carriers (see Chapter 12). Indeed, Darwin's theory of the cause of evolution was widely rejected just because people found it so distasteful, even horrifying, to cgntemplate. And, of course, this process often does not preserve species in the face of change: lirr"d *u äxtinct. Were they the prodilore than 99 percent of ali species that have "n". ucts of an incompetent designer? Or one that couldn't foresee that species would have to adapt to changing circumstances? - SY C I E N C EC, R E A T I O N I S N AN /, D SOCIETY EVOTUTIONAR t 531 'i' Many species become exti4c;! because of gql4petition, p.$de!iq4, and parasitism. Some of these interactions are so appalling that Darwin was led to write, "What a book a devils' chaplain might write on the clumsy, wasteful, blundering, low, and horribly cruel works of Nature!" Darwin knew of maggql9 that work their way up the !4q41-123$gges 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 parasites, whether parasitic wasp or human immunodeficiency virus, ill fit our concept of an 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, "such could not have been produced through natural selection." Becausenatural selection consists only of differential reproductive success,it results in "sel{ish" genes and genotypes, some of which have results that are inexplicable by intelligent design (see Chapter 14). We have seen that genomes are brimming with sequencessuch as transposable 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, and nuclear genes that have evolved to override them and restore male fertility. Such conflicts among genes in a genome are widespread. Are they predicted by intelligent design 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 or chemicals that enhance a male's reprodlrctive sllccess but shorten replodgqlivell4!!, his mate's life spen. Nor can we rationalize why a beneficent designer would shape the many other selfish behaviors that natural selection explains, such as cannibalism, siblicide, and inJanticide. : i o r b e n . r r r s / K o n k r r r r t ' r r zi I ' ] r , i L l , r Iir'rt o srltr.t'cklir'lt K a p L . r r/ u n g t s c h i c k t \{at1en / Naseng.ingc R . r u p r ' nI I e b c r r s z v k l e n lmnrrrncletizicnz C l e i c h g e r ri c h i r ' l e r\' . r l L r r u n i e r s c h i e c li Ic h ! . I F o r t p f l . rn 1 u n s : ( , r i o l g i , , e g o i s t i s c h c "C l t n t ' v r r l l u e p a c k tn r i i m r i t t e r i i c h i i b e r t r a g t ' r r oC v t o p r l ; 5 p 1 . 1 t e n e / L - i n | r u c h t l - a r k e irtl r r i V l a r r n t - - h e n. F r n c h i b , r r k e i it l c l N 1 . i r r n c l r c r r s e r u e l l eS c l e k t i o n / S l . c r r - n i , : n F o r t p f l a n z u n g s f r ak L l-el'enssp.rnnt: clcr Gt'schlechtsf..rltn e r i n . C e s c h u i s t e r L a ) t u n gS.i b l i z i r l Kirrtlestiitu n!1,i rrf.rniiz icl Evolution and its mechanisms, observed Anyone can observe erosiory and geologists can measure the movement of continental plates, which travel at up to 10 centimeters per year. No geologist doubts that these mechanisms, 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 origin of mammals played out on a human time scale,but they have documented the mechanisms that will yield such grand changes, given enough time. Evolution requires genetic variation, which originates by mutation. From decades of 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 characters (see Chapter B). These mutations can provide new variation in quantitative characters, 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 families of natr-rralorganisms do. In experimental studies of laboratory populations of microorganisms, we have seen new advantageous mutations arise and enable rapid adaptation to temperature changes, toxins, or other environmental stresses.Laboratory studies 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 include base pair substitutions, gene duplications, chromosome rearrangements, and transposition of transposable elements. No geneticist or molecular biologist doubts that the 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(seeChapters 9,7I, and 12).We have seen allele frequency differences among recently established populations that can be confidently attributed to genetic drift (seeChapter 10). Evolutionary biologists have documented 1itera11y hr,rndreds of examples of natural selection acting on genetic and phenotypic 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- g Elosir)r1,.\[rtrJgu r]g t l u . r n t it . r i ir c ' \ [ t ' r k n r a l e (l.ricrS ' ) i r r t e n ,f i a s s e n , / d . r n r e s t i z i er t Cillstotte I Unrrrcltbcl.rstrrrrr:t'n B . r s c r t p a a r a r r s L , r u s c/ l tNr c r r t r t r l ' nLrnq \'(r11Chrtlttosorttctt k r l n sL l i c h A l i o l i l e q r . r e n z..\ l l o l h ä u i i g k c i t s t - r i c h t e t cS e l e k t i o n 532 C H A P T E R2 2 Ilesisttrrz gegenril.c.rhrsektiziden / Hertrizi cle,Unkrautlerniclrtungsrlittel o Antibiotika reproduktive Isolatiorr R ' l v i . l o i . l i e / H v l . r ' i d i c i e r r r n q\.' e l bastarcliertrng . Kreuzultg A rr: uerrpqe ''' -----'_-' K)adogenese Abn'andltrng vironmental factors, ranging from the evolution of resistance to insecticides, herbicides. and antibiotics to the evolution of different diets (see Chapter 13). Speciation generally takes a very long time, but some processes of speciation can also be observed. Substantial reproductive isolation has evolved in laboratory populations, and species of plants that apparently originated by polluploidy and by hybridization have 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 documented. The two major aspects of long-term evolutiorL anagenesis (changes of chaiacters 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 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 evidence with the evidence for supernatural creation or intelligent design: thereis no sucheaidencewhateuer. Refuting Creationist Arguments U n z u J ä r r g l i c l r k e i/t i r r E n t r a r r g e l t u r g anderer l\4öglichkeiterr kurz Creationists attribute the existence of diverse organisms and their characteristics to miracles: direct supernatural intervention. As we have seen, it is impossible to predict miracles 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 positive evidence of creatiory consists entirely of attempts to demonstrate the falsehood or inadequacy of evolutionary science and to show that biological phenomena must, by default, be the products of intelligent design. Here are some of the most commonly encountered creationist arguments, together with capsule counterarguments. 1. Evolution is outside the realm of science becauseit cannot be observed. Daseinsfolmer 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 hypotheses against the predictions they make about what we should observe. Observation of the postulated processesor entities is not required in science. 2. Evolution cannot be proved. rt,idersplücl-rIiclr rr idcrlegerr urrbestreitlrar'/ Lrräkaml.risch,aus delr Präkanrbrium . Eigenheit / unergrürrdlicl.r Nothing in science is ever absolutely proved. "Facts" are hypotheses in which we can have very high confidence because of massive evidence in their favor and the absence of contradictory evidence. Abundant evidence from every area of biology and paleontology supports evolutiory and there exists no contradictory evidence. 3. Evolution is not a scientific hypothesis becauseit is not testable: no possible observations could refute it. Many conceivable observations could refute or cast serious doubt on evolutiory such as finding incontrovertibly mammalian fossils in incontrovertibly Precambrian rocks. In contrast, any puzzling quirk of nature could be attributed to the inscrutabie will 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. l l :l ;