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Metaphysics and the Origin of Species.

This is a book with a chip on its shoulder; I suspect that its author, Michael Ghiselin, is carrying a whole log. On the one hand, we are reminded constantly of Ghiselin's genius. He never has an idea which is not revolutionary, which does not challenge orthodoxy, which has not thrown light on the appalling consequences of many years of obfuscation and mistake. Even on the first page of the Preface we are told of an idea which "is now recognized as a major contribution to the philosophy of biology, and to evolutionary theory as well." Further down the same page we are promised an "entire system of metaphysics," and the discerning reader will note the deliberate echo of Ghiselin's title with those of two of the classics of the synthetic theory. Yet, on the other hand, throughout there is the subtheme of genius unrecognized, talent unappreciated. While lesser men have gone on to fame and fortune, Michael Ghiselin has labored without full appreciation. Even the blurb on the back cover, by Ghiselin's friend and long-time supporter, the philosopher David Hull, picks up on this theme. "As important as Michael Ghiselin's work has been, he is an excellent example of someone who really has not received the attention and acclaim that his work deserves."

In fact, staying for the moment with the back cover, the evidence is that Michael Ghiselin has done very nicely in the recognition stakes. Not only has he been awarded the Pfizer Prize of the History of Science Society for the best book of the year (in 1970 for his The Triumph of the Darwinian Method), but a few years after, he got a MacArthur Prize for genius. Moreover, going back now into the book, the evidence is that if the world at large decided totally to ignore Michael Ghiselin, it would have very good reason. A more constant stream of petty nastiness and invective would be hard to imagine. Everyone, friend and foe, comes in for some mean or hurtful jibe. Philip Kitcher, a philosopher with formidable mathematical skills, is told that he does not know what a "set" is. Ernst Mayr, to whom incidentally the book is dedicated, is accused of "serious unclarity." I - for let me admit that I am not exempt - am apparently so awful a thinker that Ghiselin "would be happy to agree that when Ruse studies the human species, his work is not science" (p. 129). Adrian Desmond, one of our most distinguished historians of nineteenth-century evolutionary biology, is labeled an anti-evolutionist (in the "broad sense," whatever that might mean). Even David Hull is slighted: the important papers in which he took up cudgels for Ghiselin do not find their way into the bibliography. All in all, Michael Ghiselin comes across as the kind of man, a square peg, who on finding himself in a square hole, immediately sets about making it round.

It is tempting to seize the opportunity of a review - especially one in front of our fellow evolutionists - to settle a few old scores. 1 would be less than human were I not to admit to the temptation to succumb. I am still smarting from a review written some twenty years ago of a history I penned of the Darwinian revolution. But it would be a mistake, for I know that at one level petty and nasty as he often appears, Ghiselin does not mean it personally. He may mistake leaden-handed unpleasantness for clever wit, but it is a mistake and not an intentional game plan. Ghiselin would probably admit to quite liking me, and so long as it goes no further than these pages, I will admit to the same emotion in reverse. You have to have a certain admiration for a man who offends everyone indifferently in the way that he does. Succumbing to temptation would be a mistake at another and more important level because Ghiselin really does have things of interest and importance to tell us. My understanding is that a major intent of the MacArthur awards, however they may have worked out in practice, was to support the oddball who may not fit into conventional patterns but who really did have ability and who needed time and freedom to pursue his or her ideas. This is Michael Ghiselin to a T, and never more so than as evidenced by this book under review. I happen to think that Ghiselin is wrong - dead wrong - in what he claims. But he is wrong in interesting and important ways, and in trying to unravel the knots we learn much of importance, both about evolution and its history.

What is it that Ghiselin claims and that I would critique? Let me follow Ghiselin himself, and quote his words, at length:

The literature devoted to the "species problem" includes a lot of discussion about the so-called "reality" of species. According to one very popular philosophical notion, nominalism, individuals are "real" but classes are not. This makes a certain amount of sense: a nominalist would say that this chair is real, whereas 'chair' in general or in the abstract is not. Nominalists generally go somewhat further than that, and might even say that chairs share nothing at all except the name 'chair' - hence the etymology. One does not have to be a nominalist to admit that "chair" and the one on which I sit do not have the same ontological status. In other words, one does not have to go so far as they do and deny that "chair" in general has some kind of "reality" - whatever that is supposed to mean.

In the controversies that surround the species problem, one position that has been taken is the so-called nominalistic species concept. According to this view, species are classes, classes are not real, therefore species are not real. Consequently, perhaps, they are mere conventions and have no role to play in biological thinking. The traditional response to this kind of nominalism was to deny nominalism itself, and take a "realistic" view of species. Species are classes, and they are real, so there was no problem. But the nominalistic argument made a certain amount of sense: if species are classes, how could they evolve or become extinct? It would be like sitting on chair in the abstract. So I turned the problem on its head. Species are not classes; they are individuals. The truth of the solution seemed to me self-evident, one that followed from the definitions of 'species' and of 'individual.' (pp. 13-14)

There is a lot which needs unpacking here, so let us start at the beginning with the Linnaean hierarchy. It is a system of nested sets: there are a number of levels (categories) each containing sets of organisms (taxa), with each taxon including organisms from one or more taxa at the next lower category level. All organisms are assigned to one and only one taxon at each level, and since the taxa get ever-more inclusive as one rises up the hierarchy - one stays with one's fellow taxa members as one moves upwards - one can assign each and every organism to its place in the great scheme of life. Jerry Coyne thus (in the basic seven-level version of the hierarchy) starts at the bottom by being classified with his fellow humans in the species Homo sapiens. This species and one or two others (now extinct) are included in the next-level taxon, the genus Homo (meaning that Coyne himself is a member of the set, Homo), and so up the ladder until we arrive at the category level of kingdom (where Coyne ends up as a member of the taxon Animalia). Other organisms go up the hierarchy from other starting points. Lucy, for instance, begins as a member of the species Australopithecus afarensis. Then she goes into the genus level taxon, Australopithecus. She joins up with Coyne at the next level (family), in the shared taxon Hominidae, and so up the hierarchy together to Animalia.

The big theoretical question about the hierarchy has always been about its "naturalness." Why is it so special? Why is it somehow right to put Coyne and his fellow humans in with other animals like worms and spiders, and not with plants like oaks and ferns, or elsewhere? Well, of course, the answer is that in part it is not so special. Everyone agrees that there is a sense of arbitrariness about the system, at least about how it is used. Most of us would be hard pressed to say why Coyne should not be in the same genus as Lucy, that is in the genus Afarensis rather than Homo. Some genera (and taxa of higher orders) do satisfy everyone pretty much, but the same everyone is fully aware that many taxa are about as natural as a seducer's smile. Why then does the system persist, despite the attempts to change it?

One answer is that you have to use something: biology would be impossible without classification, and tradition and inertia are on the side of the system which we do use. Another answer is that, arbitrary though classification may often be at higher levels, all agree that at the lowest basic category level - the species - there does seem to be (at least in sexual organisms) one special way in which nature has chopped itself up at the joints and the taxa we use are real. It is true that even here we have some problems of arbitrariness if we think of species through time - after all, evolution implies continuity, and Darwinian evolution implies gradual change - but thinking of species set side by side there is a real division. It is not a matter of whim or capriciousness that we insist that Coyne go in the same group as the two Michaels, Ghiselin and Ruse, and that (were they contemporaneous) he and Lucy would be kept apart forever. I am sure he would be a perfect gentleman if they were out on a date, but that is the whole point.

What is it then about the species which makes it (that is to say, taxa at the species category level) so special? Why do we think that the class Homo sapiens is real or natural or objective or some such thing? This is the "species problem" to which Ghiselin refers in the passage quoted above. We have been told endlessly by Ernst Mayr (1982) and his followers (including Ghiselin in this book), that the Platonist - the paradigmatic "realist" (using this term to refer to a venerable philosophical school which thinks that universal terms refer to real existing things) - thought that each species had some special essence peculiar only unto it, and that this distinguished one species from another. Water is uniquely [H.sub.2]O, and there's an end to it. Sulfuric acid is [H.sub.2]S[O.sub.4], and hence not water. The same with biological species. Humans are uniquely rational animals, and there's an end to that too. My dog Spencer is not rational and hence not human.

Unfortunately, as Mayr has told us equally endlessly, against a background commitment to evolution, this just will not do. The whole point about post-Origin life is that variation is the name of the game. It occurs everywhere right through every species. Indeed, without variation on each and every organic attribute, natural selection would just grind to a halt. Name anything you want to pick out as an essential attribute, and you can be sure that someone somewhere within the species will not qualify. Rationality? Try babies, Alzheimer's victims, drunks, and philosophers faced with hard decisions.

In any case, argue Mayr and company - in an argument to which I shall return for I think it reveals more than they realize - the whole attempt to provide criteria for naturalness in terms of physical characters, in a Darwinian evolutionary world, is fundamentally mistaken. Mayr (1942) himself, following Theodosius Dobzhansky (1937), defines species as "groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups." This has nothing to do with definitions in terms of physical or similar characters like rationality or (as in birds, Mayr's speciality) wing color or beak size or egg shape. It is true that one uses these characters to decide to which species one should assign a specimen. After all, for twenty years after coming to America, Mayr worked as a curator in the American Museum of Natural History, where the only living birds he ever saw were those on the way to and from work. But this, we are assured, has nothing to do with the real reason why they are in the species that they are in. By virtue of his black bib, you may recognize that friendly little bird on your feeding table as a house sparrow, but it is his sex life which makes him a member of Passer domesticus. He copulates with fellow sparrows and not with blue jays. It is this very Darwinian activity which justifies the calling of the reproductive definition the "Biological Species Concept." (In the trade, we philosophers refer to a name like this as a "persuasive definition," meaning that the very terms used are intended to push a message. In this case there is the not-so-subtle implication that this concept is uniquely the true "biological" notion.)

Platonism seems to have fallen apart. And why not indeed, after Darwin? Who now takes seriously the Creation stories of Genesis: "Hebrew old clothes," as they were described by the nineteenth-century essayist Thomas Carlyle? Why then should we take seriously the metaphysical musing of ancient Athens? But what then does this do to the whole notion of species as classes? Can one try to regroup in a weaker fashion? A number of alternatives have been tried, including one popularized by the Austrian-born philosopher Ludwig Wittgenstein, namely that one use some kind of cluster concept, listing characteristics of which a minimum number are necessary for species membership although no one characteristic is necessary. One includes babies within the species Homo sapiens because they have arms and legs and so forth, even though they may not be rational. One includes thalidomide victims because they are rational and have many other human features.

But many feel uncomfortable about this move. It seems a philosophy of desperation, quite apart from the practical difficulties. What is an arm worth? Five IQ points or ten? We seem to be on the way to the other end of the philosophical spectrum from that of realism: we seem to be on the way to the philosophy we have seen discussed by Ghiselin, "nominalism," where species (being classes) are not regarded as being real at all. A term like Homo sapiens is no more than a word, an arbitrarily applied name, which divides things up according to habit or convenience or prejudice. In itself, the class Homo sapiens has no more real standing than (say) the class of U.S. states and Canadian provinces whose names begin with "A." And this is obviously absurd, since Michael Ruse and Michael Ghiselin and Jerry Coyne do have something not possessed by Arkansas and Alabama and Alaska and Arizona and Alberta. It was Ghiselin's (1974) brilliance - let us not be small-minded in our praise - to try an altogether radical proposal to the species problem: a proposal getting right away from attempts to patch up traditional methods of classification - or rather, traditional methods of justifying classification. He proposed that species not be regarded as classes at all! Instead, we should think of them as individuals. Once this is done, we can see that their objectivity and naturalness drops right out at once.

What did this mean, exactly? Well, whatever else they may be, individuals are things and no one denies their reality. The paradigmatic example of individuals in biology are individual organisms - Michael Ruse, Michael Ghiselin, Jerry Coyne - and no one has any hesitation in agreeing that they exist, that it is a natural cutting of nature at the joints to regard them as entities unto themselves. In the same way, species are to be regarded as individuals, as things, and then at once the naturalness of using species follows. Although do note that, as the relationship for individuals is wholes and parts - my arm is part of me, the whole - rather than classes and members - Canada is a member of the United Nations - so we should recognize that for species the relationship is wholes and parts - I am a part of Homo saplens - rather than a member of the class. This gives a whole new meaning to John Donne's great elegy which starts: "No man is an island." Not only will one have to revise the patriarchal language at the beginning, but the end must now be: "Ask not for whom the bell tolls, it tolls for part of thee."

What argument is offered for this proposal? Curiously, in the book under review, although we are told that this is an attempt to lay out Ghiselin's thinking in a clear one-shot attempt, we get little by way of justification. It is almost as if Ghiselin has grown tired of making the points over and over again. At times, he is almost arrogant: "If we say that all unmarried persons are, by definition, single, and that, furthermore, all bachelors are, by definition, unmarried males, it follows logically that all bachelors are single. We can tell that this is true without having to appeal to experience, and because it follows deductively, we can say so with apodictic certitude - it cannot possibly be false. One reason why I persisted in my belief that species are individuals was that it seemed to me that it followed from the definitions of "individual' and 'species' as I understood those terms. For that reason it seemed that to claim otherwise was like denying that bachelors are single" (p. 73). Which is just too bad for those of us whose intuitions go the other way!

One argument for the individuals-as-species thesis might be that species could be considered as kinds of organisms, the paradigmatic example of individuals. This is not an obvious move to make. To put in context the title of this review, it was certainly not obvious to the satyrist Jonathan Swift when he wrote to Alexander Pope. He naturally assumed that species are not individuals: "I have ever hated all nations, professions and communities, and all my love is towards individuals. . . . But principally I hate and detest that animal called man; although I heartily love John, Peter, Thomas, and so forth" (letter of September 29, 1725). But as a scientist is surely open to one to make a counter argument: that in the biological context, species function as individuals. In fact, a suggestion along these lines was added by Dobzhansky to the third edition of his Genetics and the Origin of Species.

In organisms which reproduce sexually and by cross-fertilization, the reality of species as biological units can also be demonstrated by a quite different method. If mating and procreation are observed, it will soon be found that organisms form usually quite discrete reproductive communities. These communities consist of individuals united by the bonds of sexual unions, as well as of common descent and common parenthood. It will doubtless be discovered that one of these reproductive communities consists of animals which, on the basis of previous morphological study, were called cats, while another community will consist of lions. No lion cub is ever born to a pair of cats, nor is the converse ever observed. A species is, consequently, not merely a group and a category of classification. It is also a supraindividual biological entity, which, in principle, can be arrived at regardless of the possession of common morphological characteristics. (Dobzhansky 1951, 6) As it happens, Ghiselin is rather rude about this kind of gambit. It is apparently a form of organicist thinking which has "led to all sorts of errors" (p. 127). But I am not sure that it really is such a silly move to make. Other than simply laying down the law Ghiselin-style, you have to make some argument.

Another way, I suppose, of making a case for the species-as-individuals thesis is to play the kind of game beloved of philosophers. You make up fancy examples to appeal to intuitions. Apparently, individuals (unlike classes) necessarily have a kind of temporal continuity (Hull 1976, 1978). Suppose one discovers that one can make a brand new radioactive element, albeit an element which is very unstable. The class of members or instances of that element would remain unchanged, whether it was filled or not, and whether it was empty between instances. However, suppose some neo-Dr. Frankenstein were to make (let us say) a new Napoleon. No matter how many Napoleonic characteristics it might have - round belly, hand stuck in coat, desperate desire to march on Moscow - according to the follower of Ghiselin, it would not really be Napoleon. Biological species apparently fit the intuition that they could never reappear were they to become extinct. If some mad molecular biologist were to sequence the DNA of the new Tyrannosaurus rex ("Sue") at the Field Museum in Chicago, and then to create a new specimen (from scratch) it would not really be T. rex. Or so we are told. But of course, the trouble with examples like this is that not everyone shares the same intuitions. For myself, I am inclined to think that the chap really would be Napoleon and equally I would regard the new organism as T. rex. After all, when new specimens are formed through polyploidy, we have no problem in putting them all into the same new hybrid species - even though at times this species may have no extant representatives. Are we to deny someone the patent on a new organism simply on the grounds that logically no one could create the same organism, even if the DNA sequence were identical? If I fell in love with a newly created human-like being, would you think me a pervert? Misguided and unfortunate, perhaps. But hardly on a par with a chap who liked to have sex with cabbages.

The other perhaps more fruitful way of tackling the problem of the ontological status of species is to examine precisely what is entailed in calling something an "individual" rather than a "class." Here is surely the reason why speaking of a species as being like a super-organism does not strike most of us as so stupid, even if we decide in the end that that is not quite what we want to claim. For the point is that individuals have some kind of integration, some kind of internal ordering principle, which non-individuals do not have. That is why we are confident organisms are individuals in a way we would not regard (say) a pile of rocks as an individual. It is this integration, this cohesion, which would lead us to agree that the United States of America is an individual, even though Alaska is separated by Canada, whereas - thanks to the constitutional problems surrounding Quebec - we might question the individuality of Canada, even though there are no separated provinces.

The question which faces us now therefore is whether a species has the kind of internal integration, cohesive structure, functioning, that we associate with individuals of a more traditional kind. And here, it seems to me, history has been unkind to Ghiselin and his proposal. When he first put it forward, some twenty-five or more years ago, it seemed reasonable to respond in the affirmative. I will not say that there was a lot of hard evidence in favor of the claim that species have an internal structure, but there were ideas - claimed facts, theories even - which seemed to point that way. On the one hand, there was a lot of talk about "genetic flow" - the idea that genes move around a species, thanks to interbreeding. Remember, these were the 1960s. After Woodstock, this seemed almost an analytic truth. On the other hand, a good many people (including many of the leading evolutionists of the day) were quite favorable to the idea that selection works on groups, on species even. Hence, the integrity of the species as an individual seemed quite plausible. Unfortunately, since that time, the empirical and theoretical supports have been undermined, more than somewhat. Genetic flow as a reality has been roughed up considerably, and group selection has gone the way of phlogiston. Thanks to sociobiology, we now see that it is every organism for itself, and to hell with the group - except as an epiphenomenon of what happens at a lower level.

The science has passed by the species-as-individuals thesis. It really does not make good sense - indeed, it makes for rather bad science - to suggest that species have the integration and cohesion we associate with organisms. Or rather, let me qualify this by saying that it makes for rather bad Darwinian science to suggest that groups have the integration and cohesion we associate with organisms. Significantly, among scientists those who have been most receptive of the species-as-individuals thesis have been precisely those who are trying to break from strict Darwinism. I think here, for instance, of the paleontologists who have been arguing for things like so-called "species selection," where species do function as the basic units of change (Eldredge 1985). I will not dwell on the paradox here, that Ghiselin - the most ardent of Darwinians - has proposed a thesis of greater comfort to those who would revise and repudiate the master.

Of course, you might respond that sauce for the goose is also sauce for the gander. Perhaps today's Darwinian science proves rather more than is comfortable. If species are not individuals, then in this day of "selfish genes" can we properly regard organisms as individuals? The answer is that in respects we cannot. But remember that the biggest enthusiasts for selfish genes agree that genes come bundled in organisms and depend on the whole for their continued existence, so (to use the language of Richard Dawkins (1982)) if genes are "replicators" (and individuals at this level) then organisms are "vehicles" (and individuals at this level). I suppose it was only to be expected that at this point Ghiselin sneers rather than mounts a counter-argument: "calling organisms "vehicles" was one way of using a misleading metaphor in support of a dubious metaphysical thesis. More pernicious, because less obvious, was the choice of the term 'replicator' for genes and other things of which copies are made." (p. 147)

Species-as-individuals was a good idea, but it just did not work. It goes against the best evolutionary biology of today. So what do we do instead? Do not despair, rather let us go back to the 1930s and 1940s when the present mess began. This was a momentous time in history of evolutionary theory, for it was precisely when people like Dobzhansky and Mayr were trying desperately to upgrade evolutionary biology to the status of a professional science of the better kind (Ruse 1996). For years, their subject had languished in the museums and on the fringes of academia - condescended to by all of the better classes of scientists, including fellow biologists like embryologists and geneticists. These evolutionists had to show people (and, to be frank, to convince themselves) that they were more than just philosophers and stamp collectors and showmen, spinning fabulous phylogenies and putting specimens in boxes and preparing displays for school children. Central to this campaign was the promotion of the synthetic theory of evolution - that blend of Darwinism and Mendelism to be found in Dobzhansky's Genetics and the Origin of Species - and part of this promotion centered on the upgrading of the lowest of the low: taxonomy. To do this, a sexy new (or revitalized, because the idea is certainly in Darwin if not before) definition of species was provided, and a new name "the Biological Species Concept" (provocative, pretentious, promoting - take your choice) was provided.

Moreover, a break with the past had to be provided. On the one hand, a villain had to be found: since at that time every one seemed to be knocking Plato (read Popper's the Open Society and its Enemies (1945)), the greatest philosopher of the ancient world fell naturally into the role. On the other hand, the practices of the uninitiated had to be condemned: simply working from physical features is not classification we were told. As it happens, it is highly probable that the real Plato (that is, the Plato that can be found in his writings) had little or nothing to say about species in the way that the synthetic theorists have assumed (Kitts 1987). He, and even more Aristotle who was a working biologist, knew full well about the problems of organic classification. But no matter. As John Ford told us in The Man that Shot Liberty Valance, when truth and legend clash, go with the legend. (Ghiselin, for all his past successes as a historian, does not even bother to mention revisionist thinking on Plato.)

This was legend making with a purpose. Take the whole question of physical properties and classification. Can you possibly imagine a weirder belief than that the things you use most of the time (for many professional taxonomists, all of the time) have no significant role in the nature of proper classification? That everything depends on activities which you rarely, if ever, see? Only people in the grip of powerful sociological factors could ever have claimed and promoted quite so barmy an idea. And only people desperate to believe would have swallowed it. Or rather, only people desperate to believe would have claimed to swallow it, for as I shall argue what was claimed and what was done did not always coincide. (Honesty compels me to say that there is another group, of which I am a charter member, whose members are so scared of Ernst Mayr - especially when he is on the rampage - that we did not dare express opposition, even when secretly we were not convinced.)

Where do we go from here, in the light of the science of today, recognizing the failure of Ghiselin's proposal, no longer feeling the desperate need of a Theodosius Dobzhansky or an Ernst Mayr to prove status? When indeed, the young Turks of today (Coyne, Barton, and Turelli 1997) are happily tearing to shreds the most cherished notions of the synthetic theorists? Back to classes, I think, and dare I suggest that this time we might avail ourselves of the work that others have done in the past? I realize that the joke about philosophy is that we spend our time counting angels on the heads of pins. But sometimes some progress is made. (The trouble is that as soon as philosophers start making progress they hang their shingle out further down the corridor in a new department. First, physics. Then, psychology. Now, linguistics. Tomorrow, philosophy of biology?)

Drawing on our philosophical heritage, let me refer to the man whom I regard as the greatest epistemologist of science of the nineteenth century: paradoxically, one who was not only an ardent Platonist but so far opposed to evolutionary thinking that he refused to allow a copy of the Origin of Species on the shelves of the Wren Library, to be found in Trinity College Cambridge of which he was Master. I refer to William Whewell (pronounced "Hule"), author of the three-volume History of the Inductive Sciences (1837), which he followed some three years later with the two-volume Philosophy of the Inductive Sciences (1840). By the time he wrote his History and his Philosophy, Whewell was Knightsbridge Professor of Moral Philosophy at Cambridge. But some years earlier he had been Professor of Mineralogy. As holder of this post, Whewell was led to think hard about the nature of classification in that subject and he was led to formulate a principle of demarcation between the natural and artificial. He realized that what led mineralogists to think of a division as natural was the coincidence of a division made on one set of criteria with a division made with another set. This coming together of the logically independent was what counted. Thus, he wrote as follows about what he termed (in Platonic fashion) as the "Idea of Affinity":

The correspondence of the indications of different factions is the criterion of Natural Classes; and this correspondence may be considered as one of the best and most characteristic marks of the fundamental Idea of Affinity. And the Maxim by which all Systems professing to be natural must be tested is this: - that the arrangement obtained from one set of characters coincides with the arrangement obtained from another set. (Whewell 1840, 1,521, his italics)

As it happens, Whewell introduced his principle by quoting the work of the botanist de Candolle:

The natural classes founded on one of the great functions of the vegetable are necessarily the same as those which are found upon the other function; and I find here a very useful criterion to ascertain whether a class is natural: namely, in order to announce that it is so, it must be arrived at by the two roads which vegetable organization presents. Thus I affirm that the division of monocotyledons from dicotyledons, and the distinction of Gramineae from Cyperaceae, are real, because in these cases, I arrive at the same result by the reproductive and the nutritive organs: while the distinction of monopetalous and polypetalous, of Rhodoraceae and Ericineae appears to me artificial, because I can arrive at it only by the reproductive organs (Whewell 1840, 1, 520, quoting A. de Candolle, his italics)

However, as Whewell's friend and fellow philosopher, the astronomer John F. W. Herschel (1841), noted, this principle by Whewell stems from deep-held convictions about the nature of science itself: to wit, thoughts about when we feel that we have a genuine theory referring to the real world rather than a fiction or mere creation. The idea behind Whewell's principle of classification - the coincidence of different systems - is truly a special application of the idea that a theory is shown true precisely when and because it subsumes beneath one hypothesis many different independent branches of the field of study. This act of integration, which Whewell labeled a "consilience of inductions," was used by him to illustrate the greatness of Newtonian gravitational theory; beneath the same basic premises, one can explain both the terrestrial physics of Galileo and the celestial physics of Kepler. In biology, despite Whewell's rejection of the work, the greatest exemplar is to be found in the Origin of Species; beneath the hypothesis of evolution through selection, Darwin explains embryology, paleontology, biogeography, instinct, anatomy, and much more including systematics or classification. (It is no chance that Darwin incorporated a consilience: the influence by Whewell was massive (Ruse 1975).)

What I am suggesting then is that perhaps the way to go at the species problem is to make a virtue of pluralism. If you try to find a sole method of characterizing species and separating one group from another, if you privilege one set of activities and pretend that they alone are truly "biological," and especially if you claim that that which we do actually use has no genuine theoretical value or status, you are going to run into problems when you try to show why your method uniquely leads to a natural classification: to species which are real. Rather, we should see that species are real or natural precisely because they do separate out organisms on ground of breeding and of physical features and (probably) much more, like ecological or molecular characteristics. It is not just that we humans are not Australopithecus afarensis because we do not have sex with them, but also because we (unlike them) stand properly upright and have big brains and right about the species problem and much much more.

Of course you may argue - indeed Ghiselin does argue in the last of the snappy one-liners that I shall quote here - that this proposal does not work. "The various kinds of species concepts definitely do not pick out the same basic units" (p. 130, his italics). But we know that this is often not true - dogs and cats look different, they smell different, they sound different, they behave different, and they do not have sex together. And when it is true, then either (as in the case of sibling species) biologists strive desperately to find distinguishing features or they really do give up and agree that the divisions are not truly significant. In the case of asexual organisms, for instance, there is a lot of debate about the naturalness of species. And extending the argument out, surely a major reason why we generally are not so convinced of the naturalness of taxa of category levels higher than the species is because no consilience can be found between differently chosen features.

Returning again to the back of Ghiselin's book, as well as the blurb from Hull, we find also one from Mayr which begins: "This book will be highly praised by some readers, and viciously attacked by others." Let us not forget those, like me, who want to do both. This is an intensely irritating book with a main thesis which is surely wrong. But it is more interesting and important than many books which are polite and correct.


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DOBZHANSKY, T. 1937. Genetics and the origin of species. Columbia University Press, New York.

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ELDREDGE, N. 1985. Unfinished synthesis: biological hierarchies and modern evolutionary thought. Oxford University Press, New York.

GHISELIN, M. 1974. A radical solution to the species problem. Syst. Zool. 23:536-544.

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Book Review Editor: J. Coyne
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Author:Ruse, Michael
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Date:Feb 1, 1998
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