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Home , Adam Sedgwick, Edward Blyth, Henry Fairfield Osborn, Ray Lankester, Thomas Henry Huxley, William Whewell

The Darwinian revolution: Rethinking its meaning and significance

Michael Ruse1

Department of Philosophy, Florida State , Tallahassee, FL 32306 The Darwinian revolution is generally taken to be one of the key (a perhaps undeserved) reputation of a 3-h by a Pres- events in the history of Western . In recent years, however, byterian minister on a wet Sunday in Scotland. the very notion of a scientific revolution has come under attack, Against this, however, one can point out that the history of and in the specific case of and his Origin of science as a professional discipline is little more than 50 years old there are serious questions about the of the change (if there and that you have to start somewhere. In the case of Darwin, was such) and the specifically Darwinian input. This article consid- even 30 years ago there was no real synthesis. The tragedy would ers these issues by addressing these questions: Was there a have been if historians of science had stopped there and gone no Darwinian revolution? That is, was there a revolution at all? Was further. But this is clearly not true. In the past 30 years or more, there a Darwinian revolution? That is, what was the specific staying just with the history of evolutionary thinking, there has contribution of Charles Darwin? Was there a Darwinian revolu- been a huge amount of work on people before and after Darwin, tion? That is, what was the conceptual nature of what occurred on and on his contemporaries like [for and around the publication of the Origin? I argue that there was instance, Desmond (4)]. To name but 3 researchers, one can pick a major change, both scientifically and in a broader metaphysical out Robert J. Richards (5–8) and the work he has done on sense; that Charles Darwin was the major player in the change, German evolutionary thinking in the , before and although one must qualify the nature and the extent of the change, after Darwin; Peter Bowler (9–12), who started with paleontol- looking particularly at things in a broader historical context than ogy in the 18th century and since has written extensively on the just as an immediate event; and that the revolution was complex post-Darwinian figures in the 19th century, now extending his and we need the insights of rather different philosophies of grasp into the 20th century; and William Provine (13,14), who scientific change to capture the whole phenomenon. In some has offered detailed and brilliant analyses of the impact of respects, indeed, the process of analysis is still ongoing and genetics on the understanding of . It just has not been unresolved. the case that focusing first on Darwin led us to an inescapable dead end with respect to the rest of evolution’s history. ͉ evolution Kuhn Should we nevertheless persist with the term ‘‘revolution’’? Well, it surely depends on the case to be made. Obviously we can hirty years ago I (1) published a book with the main title The legitimately use the term revolution somewhat generically in TDarwinian Revolution. No one questioned whether or not I . No one thinks the American Revolution and the French had a real topic. There was a Darwinian revolution and my book Revolution were the same, but they did share characteristics that, was about it. Today, one could not be so sure. The idea of for example, the move from Ronald Reagan as president to scientific revolutions has been questioned; Darwin’s contribu- George H. W. Bush did not. There was a break from the old tion has been challenged; and even if you can come up positively government and this was done by a group seizing power, leading on these matters, what on earth are we talking about anyway? to dramatic changes. I see no reason we should not extend the These are the 3 questions I shall address in this article. term metaphorically. Think of the technological revolution in the Was There a Darwinian Revolution? past 20 years or so. Laptop computers are commonplace, electronic use of libraries is the norm, and search engines like Historian Jonathan Hodge (2) has been one of the strongest Google and Yahoo have transformed the gathering of informa- naysayers on this matter. He thinks that the whole talk of tion. If this does not all add up to a revolution of some kind, it scientific revolutions, something of an obsession by many histo- is hard to know what does. There is as much of a break with the rians and of science in the years after Thomas past as there was for an American ruled from Washington rather The Structure of Scientific Kuhn’s engaging and influential than . At an immediate level, the change is probably even Revolutions (3), is deeply misleading. The term is obviously taken greater. by analogy from politics and even there it is doubtful that there So if you want to extend the term revolution to science, if it are such things (at least that there are such things with common captures something of what goes on, then all power to the use. features) and in science likewise we have no reason to think that But now the question is whether the Darwinian revolution merits there are such things with common features. In any case, the talk the use. Was there a big break with the past, sufficiently is wrong-headed because it drives you to concentrate on some significant to speak of revolution? Did something big, really big,– people and events and downplay or ignore other people and events. happen around 1859, and does it still merit a special place in the In response, let us agree at once that focusing on revolutions history of evolutionary thought? In respects, our appreciation of (in science) does rather skew things in certain ways. Dwelling at what happened is even greater than it was 30 years ago: If you length on Darwin carries the danger of ignoring the contribu- tions of others in the 19th century, from the Naturphilosophen This paper results from the Arthur M. Sackler Colloquium of the National Academy of (people like the German anatomist who saw , ‘‘In the Light of Evolution III: Two Centuries of Darwin,’’ held January 16–17, 2009, homologies everywhere) at the beginning to the orthogeneticists at the Arnold and Mabel Beckman Center of the National Academies of Sciences and (people like the American paleontologist Henry Fairfield Os- in Irvine, CA. The complete program and audio files of most presentations are ࿝ born who thought that evolution has a momentum that carries it available on the NAS web site at www.nasonline.org/Sackler Darwin. beyond adaptive success) at the end. Worse, it gives the impres- Author contributions: M.R. wrote the paper. sion that unless you have something dramatic and crisis- The author declares no conflict of interest. breaking, the science is of little value. Remember, the alternative This article is a PNAS Direct Submission. to Kuhn’s revolutionary science is normal science, and this has 1E-mail: [email protected].

10040–10047 ͉ PNAS ͉ June 16, 2009 ͉ vol. 106 ͉ suppl. 1 www.pnas.org͞cgi͞doi͞10.1073͞pnas.0901011106 Downloaded by guest on October 1, 2021 like, today in 2009 the 200th anniversary of Darwin’s birth as at the end to inherit all of the glory. (Try www.darwin-legend.org opposed to 1982, the 100th anniversary of Darwin’s death. for a cross-sample of these sorts of charges.) (15) has referred to Darwin’s idea about natural There is little need to spend much time on these claims selection as the greatest ever. One could debate this (’s because basically they ’t hold much water. Let it be shouted theory of forms gives it a good run for its money), but all will out loud. Darwin did not steal from Wallace. Darwin’s ideas – certainly agree that something really big happened around and the ideas of the Origin that is – are all right there in the 35 page because of the Origin in 1859 (16). But here, let us take note of Sketch of his ideas that he wrote in 1842 (25). There was some some of Hodge’s worries. The basic question is: What are we tweaking about the nature of ; perhaps he hit in the talking about? In the Darwinian case there are 2 levels of activity early 1850s on the principle of divergence – although there are and interest. Without pretending that the divisions are com- certainly hints of that in the species notebooks – but the pletely simon-pure, there is the level of science and the level of mechanisms (natural and sexual selection) are there, as is the (recognizing that this includes things that might be structure of the argument of the Origin (more on this in a considered scientific at one end and religious or otherwise moment). Even some of the flowery passages, notably the final ideological at the other end). paragraph about grandeur in views of life, can be found in the On one hand, there is the of evolution early writings. Wallace certainly stimulated Darwin to get mov- through , the central topic of the Origin.Onthe ing, but that was it. And incidentally, if you study Wallace’s essay other hand, there is what scholars like Robert M. Young (17), carefully, you see differences from Darwin. Wallace, for in- borrowing a title from Thomas Henry Huxley (18), used to refer stance, denied the pertinence of artificial selection. Wallace to as the debate over ‘‘man’s place in nature.’’ While today we never had the term ‘‘natural selection.’’ Wallace had inclinations would never dare to use that kind of language, in essence they to group selection in a way absent from the Origin or earlier got it absolutely right. At some level, the Darwinian revolution writings. This is not to belittle Wallace. Not at all! But he was not destroyed forever the old picture of humans as somehow mirac- Charles Darwin. ulously special, symbolically and literally as touched by magic. The claims of others can be dismissed as well. Before Darwin, Admittedly, to this day Christian fundamentalists (and those of there were several people who had thoughts of natural selection other ) refuse to accept this, but it is true. Even if you and we know that he read some of them. For instance, in a think that you can still be religious, a Christian even, you have pamphlet by the breeder John Sebright, there is an explicit to rethink dramatically, emotionally even more than intellectu- reference to the force of natural selection, a reference that ally, what it means to be a human. Starting with a certain modesty stimulated Darwin to underline the words and make a comment about ourselves (19). in the margin (26). But there is no real question that these people sparked full evolutionary thoughts in Darwin, and generally the It is hard to know how one would respond to someone who last thing they wanted to do was use natural selection to promote questioned the significance of the changes at either of these 2 evolution. Edward Blyth (27), with whom Darwin was to have levels. At the level of science, changing over to the idea of very cordial and helpful correspondence (he actually drew evolution in itself is a massive change to make, whether you are Darwin’s attention to an important earlier essay by Wallace) moving from a Greek theory of eternal life without change or a explicitly denied that his thinking had evolutionary implications. more Christianized vision of the instantaneous appearance of And as far as others were concerned, pre-Darwinian (that is life. And then you add in the mechanism of natural selection, pre-Origin) evolutionists in particular, they certainly had effects used by at least 90% of today’s evolutionists, and you have an on general opinion, but not like Darwin. Chambers’s Vestiges even greater break with the pre-Origin past. At the level of undoubtedly took the sting out of evolution, so by the time that metaphysics, the change is yet deeper if that is possible. The Darwin published it was to a certain extent old hat, but it did not violent opposition of the American above-mentioned fundamen- have the effect of the Origin. The same is true of others, like talists or creationists shows that if anything could. It is not just . For all that Spencer (28), too, hit on the idea a question of who we are but also of how we should live our lives of selection, he always thought that is the chief (20). Although it is hardly the only factor, Darwinian thinking is cause of evolutionary change, and while his thinking did influ- at the center of the move to modernism, in some broad sense. ence some, including his big friend Thomas Henry Huxley, he Are we still to be subject to the old ways (women inferior, gays likewise did not swing people in the way that the Origin did. persecuted, abortion banned) or are we to look forward to a truly Having said all of this, however, there are some interesting post-Enlightenment world, with reason and evidence making the questions about the extent to which the revolution was truly running in an entirely secular fashion? Darwinian. Clearly some nuanced thinking is needed, starting Grant then that something big did happen. But are we right in with the that there was 150 years of evolutionary thinking putting it all on 1859 and the publication of the Origin of Species? before Darwin, including speculations by his own grandfather This raises my second big question. Divide the answer according Darwin. Toward a fuller analysis, divide the history of to the levels of . evolutionary thinking into 3 periods (29). The first period, from the early 18th century (the time of the French Encyclopediast Was There a Darwinian Revolution? Science and early evolutionist Denis Diderot) to the publication of the Start with one indubitable fact. There always have been and Origin in 1859, was the time when the status of evolutionary there always will be people who think that not only was Alfred thinking was that of a pseudo science: an emergent on the Russel Wallace, the codiscoverer of natural selection, unappre- cultural value of progress. Second, from the Origin to the full ciated but that Charles Darwin pinched all of the good ideas incorporation of Mendelism into evolutionary thinking, say from the younger evolutionist. It should be called the Wallacean Ϸ1930 with the work of Ronald Fisher, J. B. S. Haldane, and revolution with Charles Darwin but a minor footnote. [Brack- Sewall Wright, evolution had the status of a . man (21) is the classic exemplification.] There are other candi- There was some professional work going on, particularly in the dates for the job. Edward Blyth, an English-born Indian natu- area of phylogeny tracing, but generally evolution was a museum ralist, has long been a popular name. [Eiseley (22) was the source science, still a vehicle for thoughts of progress. Causal thinking for this one.] More recently, in an award-winning book, James was second-rate or (often) absent entirely. Top-quality work in Secord (23) argued that really it was Robert Chambers, the biology was increasingly by young researchers who turned from anonymous Scottish author of the Vestiges of the Natural History phylogeny tracing to microscope-based sciences, especially cy- of Creation (24), who did the heavy lifting. Darwin came along tology, and then on to genetics in the 20th century. Finally, from

Ruse PNAS ͉ June 16, 2009 ͉ vol. 106 ͉ suppl. 1 ͉ 10041 Downloaded by guest on October 1, 2021 1930 to the present we have a fully professional science of matter. No one denied natural selection. Very few accepted that . We entered the era of neo- (as it could be as powerful as Darwin suggested. People became it was called in Britain) or the synthetic theory of evolution (as evolutionists in droves. The number of pure Darwinians, as we it was called in the United States). might term selectionists, was very few, and the most prominent Now, frame the discussion against the background of this after Darwin himself, namely Wallace (37), became enamored of 3-fold division of history. If we consider the revolution in a broad in the 1860s and he started to deny selection when sense, from the beginning of the 18th century to the beginning it came to humans. The reasons for this halfway acceptance are of the 21st century, there are 2 major points at which we want to well known. On one side, there were scientific problems with say that it is a Darwinian revolution. The first was in the selection. It was thought that it could never be strong enough to transition from being a pseudo science to being a popular overcome the supposed averaging nature of . Even the science. Before the Origin, the evidence for evolution just was not best new variations would be swamped into nonbeing in a there. If you believed in evolution, you were fueled primarily by generation or two (38). Added to this the (ignorant as ideological reasons. It is true that people knew about homolo- they were of the warming effects of radioactive decay) denied gies, the record was starting to fill out, embryology was that there was time enough for such a leisurely process as natural suggestive, and so forth. But the full picture was not there. After selection (39). On the other side, there was the matter of the Origin, being an evolutionist was just plain common sense. adaptation. Selection does not just bring about change. It brings And people did become evolutionists. Even church people. With about adaptive change. This ran into trouble from folk at both the notable exception of American evangelicals, especially in the ends of the spectrum. German-influenced like Huxley South, evolution was accepted (30). It is true that there was some (40) thought that adaptation is but a minor phenomenon, and backsliding, in the Catholic Church especially by century’s end, hence felt no need to embrace selection on that score. Non- but overall people became evolutionists (31). adaptive saltations (jumps, what we today would call ‘‘macro- This change was thanks to Darwin, especially to the structure ’’) would do the job for evolution. Heavily Christian of the argument in the Origin. The methodologists of science of evolutionists like American botanist (41) thought that the day, more particularly, the methodologists of science of the selection could not fully explain adaptation and so they wanted 1830s when Darwin was discovering and formulating his theory, (-) directed variations. As Darwin said, this rather made insisted that the best science has at its heart a true cause, a vera natural selection redundant. causa. They differed over what is the mark of a vera causa. John So after 1859, it was evolution yes; natural selection, much less F. W. Herschel (32), with empiricist leanings, insisted that we so. This meant that the dream that Darwin had had of founding have direct sensory evidence or something analogical. We know a professional science of evolutionary studies, based on natural that a force pulls the toward the Earth because swinging selection, never really got off the ground. There certainly was a stone around on a piece of string requires you to pull the stone professional , particularly that around the German in toward you. (33, 34), with rationalist lean- (42). But, increasingly, a lot of what was ings, insisted that we justify the acceptance of our hypothesis produced lost touch with reality as fantabulous tales were spun through its implying a whole range of , thus using the unreliable biogenetic law, ontogeny recapitulates phy- manifesting what Whewell called a ‘‘ of inductions.’’ logeny. In Britain you had the incredible paradox that the chief As in a court of law, where the guilt is ascribed through the wide post-Origin evolutionist in the second half of the 19th century, range of clues that it explains. Darwin set about satisfying both a man deeply involved in and highly influential on postsecondary vera causa criteria (35). First, he argued analogically from , Thomas Henry Huxley, never taught evolution to his artificial selection (the work and triumphs of the animal and students. He thought they should concentrate on and plant breeders) to natural selection, from something known and (29). seen to something not known and seen. Then he turned around, So evolution became the subject of the popular lecture hall, and showed how evolution through selection throws light on working men’s clubs and the public-friendly British Association topics across biology, instinct, , biogeography, sys- for the Advancement of Science, and the leading evolutionists tematics, , embryology, and more. As evolution through moved from the to the museums. Huxley student E. selection explains, so conversely the explained areas justify our ran the (Natural History) in in evolution through selection. London and Huxley student ran the There are questions about how effective was the appeal to American Museum of Natural History in New . And what artificial selection. Generally before the Origin it was taken as a you want in museums are displays, with an educational and reason not to believe in ongoing change (no one has turned a cultural message. So this is what was supplied. Terrific displays horse into a cow) and I have mentioned how Wallace denied of , especially of all of those now being discov- explicitly that it was relevant to the evolution issue. After the ered and brought back from the American West, and all put in Origin, people like Huxley took the failure to create new species a progressive fashion to demonstrate that life may have started artificially as a reason to hesitate before full acceptance of as blobs but that it ends as humans, especially white humans. natural selection’s powers. However, undoubtedly at some level Finally, Ϸ1930 came the move from popular science to the analogy softened people up to evolution. Part of Darwin’s professional science. First there were the mathematicians, the genius was always to put his ideas into comfortable contexts. He population geneticists mentioned above. Then came the empir- argued to natural selection via the , which icists, the experimenters, and naturalists, who put flesh on the was something that came out of the thinking of the Reverend mathematical bones: E. B. Ford and his school in Britain and (36), who pointed out that population Theodosius Dobzhansky and his fellow evolutionists in the demands will always outstrip potential gains in space and food. United States. Now we had university posts, researchers, grad- Everyone knew about these Malthusian calculations, and, even uate students and grants, journals, societies, and everything else if they did not much like them, generally they accepted the we associate with professional science, and not just at the conclusions. Likewise with the world of breeders, people at least sociological level, because the work produced was firmly based took some comfort from the arguments provided by Darwin, on empirical studies with mathematical models doing the ex- even if they were not definitive. plaining. The epistemic virtues of science (consistency, coher- The consilience was a different matter. Here, Darwin did ence, predictability, fertility, simplicity) were taken seriously and persuade. At least, he persuaded to a point. As noted, evolution the worth of work was judged by its success against these virtues. after the Origin was nigh a truism. The mechanism was another And right at the heart was natural selection, which continues to

10042 ͉ www.pnas.org͞cgi͞doi͞10.1073͞pnas.0901011106 Ruse Downloaded by guest on October 1, 2021 this day. Here, again then Darwin has made a major contribution cally, one thinks of , a movement that covered to evolutionary studies. many different ideologies and that generally owed more to Herbert Spencer than to Charles Darwin (49). When, to take a Was There a Darwinian Revolution? Metaphysics particularly egregious example, German general Friedrich von What of the Darwinian revolution in the broader sense, the side Bernhardi (50) claimed that Darwin showed that might is right dealing with our metaphysical view of ourselves, our place in and that the Motherland has almost an obligation to seize from nature? Here, Darwin was crucially important if not completely its neighbors, he owed little to the old evolutionist who had successful. He himself was stone-cold certain that we humans are worked away in his study in the English countryside. One might part of the world of nature. His experience with the native people as much credit Plato because the doctrine more closely resem- from the bottom of South America, the Tierra del Fuegians, had bled the thinking of Thrasymachus in the Republic. Today one convinced him of that (43). And he made his case publicly, as is has similar divisions. For instance, Peter Singer (51) well known, not in the Origin (which was somewhat reticent on has claimed the authority of Darwin for an explicitly left-wing the human question) but in the Descent of Man, published some manifesto. Philosopher Larry Arnhart (52) has no less enthusi- 12 years later in 1871 (44). However, now we must ask what it astically claimed Darwin’s support for a right-wing view of means to put ourselves in nature. There are 3 possible answers. society. First, it can simply be to make humans part of the natural order Second, it must be appreciated that (apart from those who of things. We are ruled by the laws of and chemistry and reject the naturalistic program in itself) there are those who biology and so forth just like anything else. Second, it can be argue that natural selection is not the appropriate tool to analyze showing that natural selection was the chief causal force making human nature. Clearly a lot of social think this, but so us what we are, and perhaps that selection is still significant. also do prominent biologists. The Harvard geneticist Richard Third, it can be to claim that we are no different from anything Lewontin, a committed Marxist, is one who denies that evolu- else, at least in value or worth. An oak tree, a wart hog, a human, tionary biology is the key to understanding Homo sapiens.He ontologically and axiologically they are the same. opts rather for economic and like forces (53). It may well be that If you are thinking of the first of these claims, if you think of the late shared his sentiments. With some few the Darwinian revolution as an attempt to make humans entirely exceptions, notably Elliott Sober (54) who has not only argued natural, in the sense of produced and working according to the for the influence of selection on our modes of thinking in the same laws of nature as everyone else, one can truly say that for many people this revolution has succeeded and Darwin played realm of science but who has also coauthored a spirited defense a major role in its success. The Origin put us firmly in the natural of the selection-based nature of human morality (55), the picture and then following up the Descent of Man was a major philosophical community feels negatively inclined to the selec- analysis of humankind from a naturalistic perspective, covering tion-explains-humans program. The particulars are thought not just our physical frames but also our moral beliefs and social wrong; feminist philosopher Lisa Lloyd (56) launched a heavy and intellectual natures generally. No one would want to say that attack on the putative biological basis of the human female it was Darwin alone. Huxley and his Man’s Place in Nature (18) orgasm. But more importantly the overall program is declared was a key figure back then and of course there have been literally ideological and inadequate. Even those who think there might be hundreds of other contributors, in and out of biology, since. But a possibility of a selection-based approach to human nature Darwin deserves his name up there. Even those who may not declare regretfully that the quality of the work produced thus far much care for the work actually being produced seem to agree falls far short of the standards of adequate science (57, 58). that the naturalistic program is the right one and that it must take We come to the third claim, namely that we humans are not evolution into account. Although having said this, it must be in any way special. You might think that proving this was admitted that there are many for whom this program is unac- Darwin’s intent; after all, he did caution himself never to use the ceptable, and who would deny that Darwin has succeeded or terms ‘‘higher’’ and ‘‘lower’’ (writing this on the flyleaf of his indeed could succeed. The official Catholic position, for in- copy of Vestiges) and the mechanism of natural selection is stance, is that we have and these are created and inserted nothing if not egalitarian. What is it better to be, the AIDS virus miraculously into human frames, actually, human zygotes (45). or a lowland gorilla? Speaking purely biologically, there are few And this obviously is but one end of the spectrum that goes all who would speak up for the ape. However, it cannot be gainsaid of the way, through the kind of directed evolution allowed by that if this was indeed the intent of the Darwinian revolution it some members of the theorists (46), across to would have been news to Darwin himself. He always thought of the hard-line young earth creationists who think that humans humans as being at the top of the tree of life and European were created miraculously on the sixth day (47). humans as being on the highest branches of all (6, 29). Indeed, Second, what about natural selection? Again, Darwin is very in later editions of the Origin he added material suggesting that important, perhaps indeed more important than just the natu- natural selection leads to progress and ultimately to intelligence. ralism part. The Descent of Man showed in detail how natural He invoked what today’s evolutionists call ‘‘arms races’’ where selection (combined with sexual selection) is a crucial explana- lines compete against each other, improving in the tory factor behind much that we think of as human, physical, and process, and argued that eventually this would lead to intelli- social. This is a path that many have followed, most notably in gence and progress. recent times by Harvard biologist Edward O. Wilson in his On Human Nature (48), a work that covers morality, , If we take as the standard of high organisation, the conflict, and much more. Wilson is not a hard-line evolutionary amount of differentiation and specialization of the sev- determinist, but he does argue that (in his language) the twig is eral organs in each being when adult (and this will bent. The human mind is not a tabula rasa but shaped by the include the advancement of the brain for intellectual forces of natural selection. And many workers in the evolution- purposes), natural selection clearly leads toward this ary field today would agree, from physical anthropologists standard: for all physiologists admit that the specializa- through human behavioral ecologists and on to evolutionary tion of organs, inasmuch as in this state they perform psychologists. their functions better, is an advantage to each being; and However, 2 reservations must be expressed. First, much that hence the accumulation of variations tending toward has been claimed in the name of Darwinian selection bears but specialisation is within the scope of natural selection. a passing resemblance to the program of the Descent. Histori- Darwin (59)

Ruse PNAS ͉ June 16, 2009 ͉ vol. 106 ͉ suppl. 1 ͉ 10043 Downloaded by guest on October 1, 2021 Although most of Darwin’s contemporaries did not rely on theory can be shown the special consequence of another theory. selection, they, too, virtually automatically assumed that evolu- Supposedly the macroscopic understanding of gases (Boyle’s law tion was progressive, with humans at the top. One possible and so forth) could be shown a special instance of the kinetic exception was the older Thomas Henry Huxley who in 1893, 2 theory of gases. years before his death, argued that evolution is not progressive On the other hand, we have the revolutionary view of Thomas and that if we are to succeed morally we must conquer the Kuhn (3). Here, the change is abrupt. In Kuhn’s terminology we evolved beast within (60). Perhaps even he thought we are go from one to another, and there is no continuity. special it is just that we must use our evolved moral senses and Hence, the change of viewpoint, from one paradigm to another, intelligence to claim our rightful places at the top. can never be fueled by reason. It always has to be more of a Where do we stand today? Few actual working scientists are conversion experience. This is the reason there is often such going to make any such claims, especially not in their science. bitter fighting between scientists. There is no common or shared The exceptions, people like the paleontologist Simon set of beliefs that can be decisive. As with political disputes, Conway Morris (61) who argues that there are niches and that everyone argues from within their own system. organisms seek them out and occupy them and that at the topic Without wanting to homogenize everything into a gray bland- is the intelligence-cultural niche that we humans uniquely have ness, it is probable that both positions have things to say that found, tend to keep such speculations for books that are aimed throw light on Darwin and his achievements. Clearly, as the at the general audience. Moreover, there are those, Stephen Jay logical empiricists would lead one to expect, in some respects Gould (62, 63) was a leader in this respect, who would say that Darwin was replacing old positions with new ones. If you think there is no progress and that the Darwinian revolution shows for instance of Darwin’s old friend and mentor, the violently that there cannot be. Ultimately, natural selection is not a antievolutionist, Cambridge paleontologist progress-producing mechanism. So we could say that the Dar- (67), Darwin is simply saying that Sedgwick’s reading of the fossil winian revolution does prove the nonspecial status of humans, record is wrong. Sedgwick argues that there are and always will and finally today people recognize the fact. However, this may be gaps in the record and that these represent real breaks in the not be the entire . A case can be made for saying that still continuity. Darwin is saying that the gaps are artifacts of today the popular perception is of progress leading to humans. incomplete fossilization and that there were bridging organisms, That was Gould’s lament. Surveys suggest that this is what even if we never find them, although that should never stop us schoolteachers, even those favorable to evolution, tend to teach in the pursuit of such links. An analogous argument holds for the to their students (64). And museums as often as not give the problem of the pre- period. At the time of the Origin, same impression. Go to the Museum d’Histoire Naturelle in there were no organisms at all from this period and their absence Paris and find that the display starts with blobs and ends with you was rightly taken as a major problem for Darwin’s theory. The yourself on television. If you are in any doubt as to the message, earliest organisms of all, like , were highly complex and the floor above has a display of technology from the crudest sophisticated . How could they have just arrived on beginnings to the sophisticated forms that we have today. the scene? Sedgwick said simply that there were no pre- Summing up: Darwin played a major role in moving us to a Cambrian organisms. Darwin said that they had existed. Two naturalistic view of human nature, although there are those conflicting views and as Darwin’s overall theory was accepted, (generally if not always working from a religious perspective) Sedgwick was pushed out. Today we have many such organisms, who would deny that this can ever be done completely and and we know that Darwin was right (68). We had a simple case successfully. Darwin played no less (and perhaps more of) a role of one theory being right and the other wrong, and the right one in convincing people that natural selection is the key causal pushing out the wrong one. factor in molding and perhaps today controlling human nature, What about reduction? One does not see any cases of whole although one should be wary of all that is claimed in his name positions being taken up by Darwin’s theory, but if you look at and now there are many more critics (not necessarily religious) the range of other pre-Origin positions, talk of reduction does not who are uncomfortable with this program and would reject it in seem entirely inappropriate. Think of the position of someone part or in whole. One can make an argument that Darwin paved like , deeply influenced by the Naturphilosophen. the way for a view of humankind that gives us no special status In a work like On the Nature of Limbs (69), it is hard to say if he here on this earth, although this was certainly not Darwin’s own is actually endorsing evolution; the answer is that he probably aim and, especially in the public domain, beliefs privileging was but that he wanted to be sufficiently ambiguous to escape the humans persist today. critics. (Even as it was, Sedgwick was highly suspicious.) More importantly, although Owen certainly does not deny adaptation, Was There a Darwinian Revolution? he stresses in a very big way. Now when Darwin comes Finally, how does one analyze conceptually what happened along with the Origin, he is certainly not going to stress homology because of the Origin of Species? Let us start with 2 basic theories over all other things as did Owen, but he is not going to deny it of theory change. On one hand, we have the fairly traditional either. Most interestingly, he argues that it follows as a conse- view, represented by the logical empiricists like Ernest Nagel quence of evolution through natural selection. (65) and Carl Hempel (66). This view tends to stress continuity, with moves made driven by the evidence and reason. To a certain It is generally acknowledged that all organic beings have extent, there will be replacement of old theories by newer, truer been formed on two great laws: unity of type and the theories. Something like this happened when Copernicus conditions of existence. By unity of type is meant that knocked out Ptolemy. But there will probably be continuity. fundamental agreement in structure, which we see in There was in the Copernican case. It was the same world that the organic beings of the same class and which is quite two were describing: the same earth, the same sun, the same independent of their habits of life. On my theory, unity moon, the same planets, the same stars. Both sides agreed that of type is explained by unity of descent. The expression circular motion must be preserved. Both sides used epicycles and of conditions of existence, so often insisted on by the deferents. It is true that almost all of this was changed as the illustrious Cuvier, is fully embraced by the principle of years went on, but the growth of science was evolutionary not natural selection. For natural selection acts by either revolutionary. You can have revolutions, but they are gradual now adapting the varying parts of each being to its not abrupt, and important is the notion of reduction, when one organic and inorganic conditions of life; or by having theory is absorbed in another, or more accurately when one adapted them during long-past periods of time: the

10044 ͉ www.pnas.org͞cgi͞doi͞10.1073͞pnas.0901011106 Ruse Downloaded by guest on October 1, 2021 adaptations being aided in some cases by use and disuse, than , Charles Darwin’s mathematically gifted being slightly affected by the direct action of the external son. So Charles Darwin was not allowed to forget or escape the conditions of life, and being in all cases subjected to the problem. However, even though in the end they simply had to several laws of growth. Hence, in fact, the law of the disagree, neither Charles Darwin nor Kelvin thought that the conditions of existence is the higher law; as it includes, disagreement was personal or ideological. It was just not that sort through the inheritance of former adaptations, that of of difference (78). So in the sense that there were differences of unity of type. that sort, differences where because of rival metaphysical views Darwin (16) people talked past each other, one could claim that the Dar- winian revolution was Kuhnian. This is what theory reduction is all about. Darwin would not have There is another way in which Kuhn’s thinking is insightful. A accepted every aspect of Owen’s thinking. But there was con- paradigm is a world picture, within which a works, that tinuity, with older ideas being absorbed into newer ones, and this gives him or her tasks for the future, and which seems obvious is an important thing to note about Darwin and his work and his or certain in some sense. Obvious or certain in the sense that (as importance. just noted) you cannot see the point of view of others not in the Now let us express some sympathy for the Kuhnian view. Take paradigm (79). Think again of the divide in biology between the question of homology and pick up on the point where Darwin formalism and functionalism and put it in a broader historical and his supporters would break with Owen. Huxley (70) brings context. As pointed out, on one hand we have the out this opposition in his Croonian lecture on the adaptive side to organisms, what he called final causes, meaning skull, given at the Royal Society the year before the Origin that the parts function for the benefit of the whole. On the other appeared. He faulted Owen for being an idealist rather than a hand, we have homologies (isomorphisms) where the parts may naturalist, claiming (correctly) that for Owen the archetype well be used for different ends. Down through the ages people represents a divine platonic pattern rather than something have continued to note these 2 sides to organisms, and interest- produced purely by mechanical laws. As it happens, he also ingly people tend not to be ecumenical on the matter. Like claimed correctly that this led Owen to see more than was Darwin, they are partisans for one side or the other. Either they justified, namely that the skull is made from transformed ver- opt for function with form secondary or form with function tebrae, a claim that Darwin had accepted and that he dropped secondary. What is fascinating is the way that this divide goes smartly before the Origin appeared. The point is that, evolution- right across the Darwinian revolution. At the beginning of the ist or not, Owen did have a vision of the world that was 19th century one had formalists who did not accept evolution, fundamentally different from that of Darwin. And it persisted many of the Naturphilosophen for instance. The philosopher after the Origin, as he tied himself in knots over the hippocam- Hegel (80) is a case in point. One also had functionalists who did pus, present or not in humans and apes (71). It was not the not accept evolution. The great French comparative anatomist as such that counted, but different visions of reality. (81), with his theory about the conditions of So in this sense, we do have something Kuhnian going on, existence (that he explicitly tied to final-cause thinking), was one different if you will. But note that it is not just a such person. Then at the time of the Origin we have people who question of evolution or not evolution, and certainly not of crossed the evolutionary divide who were one or the other, but selection or not selection. Nor is it a simply matter of biblical not both. Darwin was a hard-line functionalist. That is the whole literalism. There were literalists, increasingly in the American point of natural selection. Huxley equally was a hard-line for- South, but by and large this is not an issue in the debate around malist (82). That’s why he could not see much need of natural the Origin. Literalism had more to do with a defense of slavery selection. Today, the differences persist. Take the 2 great than with the interpretation of fossils (20, 72). The big religious popularizers of evolution, Englishman and critics like Sedgwick and Bishop Wilberforce all accepted an old American Stephen Jay Gould. Dawkins (83, 84) is and always has earth and a lot more. It is rather ‘‘man’s place in nature’’ that was been an ardent functionalist. For him, it is adaptation all of the at stake. Owen was on one side. So was Sedgwick. Darwin’s great way and the only problem really worth solving. He thinks natural American supporter Asa Gray was on this side, too, a point that selection is a universal law of nature. Gould (63, 85, 86) was Darwin saw, when he grumbled that Gray’s appeal to directed notoriously ambivalent about natural selection and function, variations took the discussion out of the realm of science. And thinking it a holdover from English natural , and he we could include more, especially Darwin’s old friend the again and again stressed form. This was the central message of , who staggered across the evolutionary his famous paper on spandrels, cowritten with geneticist Richard line but bitterly regretted having ‘‘to go the whole orang’’ (73). Lewontin (87). On the other side, we have Darwin and Huxley (for all that the I would argue that in a real sense we have Kuhnian paradigm latter downplayed the significance of selection). And also there differences operating here. Different visions, unable to bridge was Joseph Hooker, the botanist, and increasingly a host of the gap (88). I find it interesting that metaphors are involved, younger workers who did not depend on church appointments things that Kuhn stresses as being important in paradigm think- for their incomes and who wanted to work and think in a secular ing. We have the organic world as a human artifact. [See fashion. Darwin’s use of this metaphor in the little post-Origin book on And in confirmation of Kuhn, this is where we tend to get the orchids (89).] We also have the organic world as a snowflake nastiness: Sedgwick (74, 75) writing irate letters to the newspaper [Kant’s 1790 picture (90)] or as a crystal [used by Whewell (91)]. about Darwin’s methodology; Bishop Wilberforce (76) sneering Admittedly, this sense of paradigm does not fit exactly with the at Huxley’s ancestry; Owen (77) doing everything he could to senses of paradigm found in the Structure of Scientific Revolu- give the Darwinians a bad name; and so forth. There were tions. For a start, both sides do recognize some of the merits of certainly vigorous debates about the science, but rarely did the the other side. It is hard to think that the ontologies are science itself cause unpleasantness. It was always (as in the completely different. For a second, with respect to the same Huxley–Owen squabble over the brain) in the cause of the bigger things 2 people could be in and out of different paradigms. With metaphysical picture. Very instructive is the age-of-the-earth respect to homology, Owen and Huxley were divided over the question. William Thompson (later Lord Kelvin) did idealistic/naturalistic issues, and yet with respect to thinking that not much like Darwin’s naturalistic approach to humankind, but homology more important than function, they were together. he objected publicly to the long time span that Darwin needed. Third, perhaps most importantly, the 2 paradigms (without As it happens, Thompson’s research assistant was none other prejudice, let us call them this) persist, down through the ages.

Ruse PNAS ͉ June 16, 2009 ͉ vol. 106 ͉ suppl. 1 ͉ 10045 Downloaded by guest on October 1, 2021 It is not a matter of one beating out the other. It is true that today to tease strands apart and consider them individually as we try functionalism has the upper hand, but things could change. In to understand and to assess what is going on. fact, in the past 20 years things have moved, with evolutionary There are other controversies (unmentioned thus far here) development enthusiasts coming onside in a very strong way for very active today. Often these involve not just the events directly formalism. The homologies they find, for instance between around Darwin but aspects of the broader picture. Robert J. humans’ and fruitflies’ genetic sequences, strike them as abso- Richards (who has been noted as a major contributor to the lutely fundamental and calling for a total revision of evolutionary history of evolutionary biology) argues that the post-Darwinian thinking. period, especially that influenced by the German evolutionist Ernst Haeckel, was much more pure-Darwinian than people The homologies of process within morphogenetic fields have recognized. He thinks that Darwin was deeply Romantic in provide some of the best evidence for evolution, just as his thinking, influenced by the currents that came from Germany skeletal and organ homologies did earlier. Thus, the at the beginning of the 19th century, and that after the Origin evidence for evolution is better than ever. The role of people like Haeckel were simply responding to and building on natural selection in evolution, however, is seen to play that which was already there (7, 9). Other students of the period less an important role. It is merely a filter for unsuc- (including myself) disagree strongly, thinking that (as cessful morphologies generated by development. Popu- noted) Darwin was quintessentially English in his thinking and lation genetics is destined to change if it is not to become that it is right to see Haeckel as responding to non-Darwinian as irrelevant to evolution as Newtonian is to themes, an attitude that inflected evolutionary biology until the contemporary physics. synthesis of the 1930s (95). Another controversy centers on the Gilbert et al. (92) work and interpretations of Peter J. Bowler (also noted above as We shall have to see how this all pans out. An ardent Darwinian a major contributor). He agrees that post-Darwinian thought like me is less than overwhelmed (93, 94). But then I am an was deeply non-Darwinian, but he nevertheless thinks that it was ardent functionalist, so I am proof of the point I am making good-quality science and that it fed smoothly into the synthesis. about the divide. Obviously, the ideas do persist and not just as Indeed the latter would not have occurred without the former fossils. (11, 12). Others, again including me, disagree strongly, arguing that post-Darwinian evolutionary biology was often really poor- Conclusion quality science (notoriously following Haeckel in spinning un- If the point being made now is well taken, then perhaps Hodge sustainable analogies between embryology, ontogeny, and pale- was right all along. There was no Darwinian revolution. The ontology, phylogeny) and that the synthesizers of the 1930s had paradigms of form and function went in before Darwin and came to cleanse the Augean stables and return to the thinking of the out after Darwin. This taken as a general conclusion is obviously Origin (melded admittedly with the new genetics) before further false. Because of Darwin and the Origin of Species, major things advance was possible (29). did happen in biological science. Less paradoxically, let us say These controversies, however, must be the topic of another that a complex phenomenon like the Darwinian revolution essay. Here, I rest confident that I have shown why, for a demands many levels of understanding. Blunt instruments will philosopher and historian of science, analyzing the Darwinian fail us as we try to understand scientific change. It is necessary revolution is such a worthwhile challenge.

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