Teleology: yesterday, today, and tomorrow?

Stud. Hist. Phil. Biol. & Biomed. Sci, Vol. 31, No. 1, pp. 213–232, 2000  2000 Elsevier Science Ltd. All rights reserved. Printed in Great Britain 1369-8486/00 $ - see front matter www.elsevier.com/locate/shpsc Pergamon

Teleology: Yesterday, Today, and Tomorrow? Michael Ruse* Teleological explanations in evolutionary biology, from Cuvier to the present (and into the future), depend on the metaphor of design for heuristic power and predictive fertility.

There is something distinctive about biological explanation, particularly about evolutionary biological explanation (Nissen, 1997). In the physical sciences, it is inappropriate to ask questions which demand explanations making reference to future events. One would never ask a question about the function or purpose of the moon anticipating a response that the function or purpose was some future happening such as causing the tides to ebb and flow. It is true indeed that the moon does cause tides to ebb and flow, but that is not its intended functional purpose. In the biological sciences, however, particularly in those areas dealing with evolution, it is fully appropriate to ask questions of this ilk. One can ask about the function or purpose of the diagonal plates down the back of the dinosaur Stegosaurus, and valid responses are that the plates exist in order to scare off predators or to attract mates or (as is thought highly probable today) to help with heat regulation (Lewontin, 1978). Forward-looking explanations of the kind just given are referred to as ‘teleological’. It is my intention to explore precisely why such teleological explanations are thought appropriate in evolutionary biology, but not in the physical sciences. As a supplementary question, I ask whether or not one might expect such teleological explanations to exist indefinitely. Or are they mere props, doomed to extinction as evolutionary biology develops and matures? Because I am myself an evolutionist and because I believe that answers to the present and future are often to be found in the past, I will structure this paper into three parts. The first will deal with preevolutionary biological thought in a teleological mode. The second will deal with

* Department of Philosophy and Department of Zoology, University of Guelph, Guelph, Ontario, Canada N1G 2W1. Received 13 April 1999; in revised form 4 November 1999.

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teleological explanations as they exist in evolutionary thought, particularly as they exist in evolutionary thought after the publication in 1859 of Charles Darwin’s Origin of Species. The third and final part will look at questions of structure and meaning, and try to throw light on the future fate of biological/teleological explanations. 1. Pre-evolutionary Teleology From our perspective, the most important pre-Darwinian non-evolutionary biological thinker was the early nineteenth-century French scientist, the father of comparative anatomy, Georges Cuvier (1813, 1817). He was not the first teleologist, for indeed teleological thought goes back to the Greeks. Aristotle was a major influence on Cuvier, although probably a more immediate influence was the eighteenth-century German philosopher Immanuel Kant. (Cuvier was born in a border state and educated in Germany.) But whatever the sources, teleological thought is absolutely central to Cuverian biology. He argued that the key organizing principle of living forms is that they are not just randomly thrown together. They exist rather in a self-coordinating fashion, with the parts integrated towards the well-being and fulfilment of the whole. Cuvier referred to this organizing principle as the ‘Conditions of Existence’, defining it formally thus: As nothing may exist which does not include the conditions which made its existence possible, the different parts of each creature must be coordinated in such a way as to make possible the whole organism, not only in itself but in its relationship to those which surround it, and the analysis of these conditions often leads to general laws as well founded as those of calculation or experiment. (Cuvier, 1817, vol. 1, p. 6; quoted in Coleman, 1964, p. 42)

The conditions-of-existence principle played a major part in Cuvier’s thinking, because he thought that through it he had a method of investigation which would enable him to bring order and understanding to the biological world. An order and understanding no less than his contemporaries were bringing to the worlds of physics and chemistry. In particular, Cuvier argued that precisely because organisms are integrated and directed towards the well-being of the whole—because they function in such a way as to serve the end of the complete organism—we can deduce from some few parts of the organism how the whole must function, and hence what shape it must have had. Thus, Cuvier argued that if by chance one were given just a tooth of an unknown mammalian form, one could proceed from there to infer the life style and habits and even the structure of the whole organism. Such tooth would at once reveal whether the organism was meat-eating or herbivorous. And if, let us suppose, it prove to be meat-eating, one can immediately exclude the possibility that the organism has hooves like a horse, or a stomach like a cow. Rather it must have the attributes necessary for hunting and catching prey, as well

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as for then tearing the victims apart and eating and digesting large chunks of raw flesh. One or a few parts thus dictate the nature of the whole: and note that the key underlying principle is one of teleological thought. Because the parts exist for the future benefit of the organism, one can spell out and infer the nature of these various parts from just a few sample items. Not only did Cuvier think that his teleological stance gave him a method of inferring the nature of unknown organisms, but he believed also that this led straight to a natural ordering of organisms. Cuvier argued that in practice the ‘Conditions of Existence’ translates into something which he knew as the ‘Correlation of Parts’. ‘Hence none of these separate parts can change their forms without a corresponding change in the other parts of the same animal, and consequently each of these parts taken separately, indicates all the other parts to which it has belonged’ (Cuvier, 1813, pp. 90–1). From this correlation, one can infer that organisms fall naturally into a fixed number of groups and subgroups. This comes through the ‘Subordination of Characters’. The parts of any animals possessing a mutual fitness, there are some traits of them which exclude others and there are some which require others; when we know such and such traits of an animal we may calculate those which are coexistent with them and those which are incompatible. (Cuvier, 1817, vol. 1, p. 10; quoted in Coleman, 1964, p. 77)

Thus, for instance, if an organism has a backbone—if it is a vertebrate—then one knows at once that it must have an internal structure of a particular kind (Fig. 1). It would not be compatible with a backbone to have (say) a digestive system or circulatory system which we find characteristic of insects or arachnids. Then, if one has a vertebrate with a stomach of a particular kind, let us say ruminant, then one knows at once that this group cannot contain organisms which are carnivores. It can hold only those organisms which are suited for ruminant-type existence. And so on and so forth until one comes down to the individual organism. Working outwards from this principle, Cuvier argued that there are four major divisions or embranchements: the vertebrates, molluscs, articulata (insects, spiders, and so forth), and radiata. A crucial consequence of the Cuverian organic world picture is that evolution is not simply empirically false, but at some deeper conceptual level totally impossible (Ruse 1979, 1996). If organisms are tightly organized teleologically, then the very possibility of a passage from one form to another is precluded, virtually by definition. Transitional forms would be teleologically suited neither for the parent way of life, nor for the offspring way of life. Their parts would fail to serve in an integrated fashion the end of the organisms’ overall well-being. It is therefore for this reason that not only does one not find transitional forms between the embranchements in real life, but that one knows that such a search is doomed to failure.

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Fig. 1. Drawings of (a) a quadruped bent over backwards and (b) a cuttlefish. From Cuvier (1830, p. 179).

There can be no links between classes, and hence there can be no evolutionary transitions down through the ages. Cuverian teleology was the mainstay of much biology in the half century or more before 1859, the year in which Darwin published his evolutionary ideas in the Origin of Species. It was taken up and elaborated by biologists both within France and abroad, particularly in Britain where Cuvier’s ideas were rapidly absorbed and promoted. It was also taken up by theoreticians of science. The endfocused way of thought that is inherent in the conditions-of-existence principle fitted naturally and smoothly with much of the philosophical and theological analyses which were then being developed and promoted. In Britain, in particular, this was the heyday of natural theology: most significant and trumpeted was the argument from design (for God’s existence), the so-called teleological argument. The supposed design-like nature of organisms was taken as direct and immediate proof of the existence of an Artificer in the Sky: the Christian Deity (Paley, 1819). One finds that important commentator on the sciences, William Whewell, devoting much attention in his History of the Inductive Sciences (Whewell, 1837) to Cuvier and his conclusions. Then, in the Philosophy of the Inductive Sciences (1840) Whewell makes a Cuverian form of teleology absolutely central to analyses of organisms. In particular, Whewell subsumes teleology under what he calls the ‘Fundamental Idea of Final Cause’. Stones slide from a rock down the side of a hill and cause it to be smooth; the smoothness of the slope causes stones still to slide. Yet no one would call such a

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slide an organized system. The system is organized, when the effects which take place among the parts are essential to our conception of the whole; when the whole would not be a whole, nor the parts, parts, except these effects were produced; when the effects not only happen in fact, but are included in the idea of the object; when they are not only seen, but foreseen; not only expected, but intended: in short when, instead of being causes and effects, they are ends and means, as they are termed... Thus we necessarily include, in our Idea of Organization, the notion of an end, a purpose, a design; or, to use another phrase which has been peculiarly appropriated in this case, a Final Cause. This idea of a Final Cause is an essential condition in order to the pursuing our researches respecting organized bodies. (Whewell, 1840, vol. 2, p. 78)

Naturally enough, Whewell was happy to follow Cuvier not only in his biological thinking, but also in his conclusions that evolution is not only empirically false, but in a deeper sense conceptually impossible (Ruse, 1977). This comes out particularly strongly in his (Whewell, 1845) responses to the anonymous evolutionary tract Vestiges of the Natural History of Creation (published in 1844 and now known to have been authored by the Scottish publisher Robert Chambers (1844)). One should say, and this is important for our subsequent story, that Cuvier and his followers did not have things entirely their way. There were those who denied that organisms are as tightly fitted to their environments, and as well-coordinated internally, as a Cuverian approach to nature would imply. More importantly, there were those who argued that the whole emphasis on functional teleology detracts from important, perhaps even more important, alternative aspects of the living world. In particular, in Germany the so-called Naturphilosophen—the transcendental morphologists—stressed that, in addition to direct functionality, organisms show striking aspects which have no immediate ends (Richards, 1992). In this they were paralleled in France by Cuvier’s great anatomical rival, Geoffroy Saint-Hilaire (1818). Then later in England, they were followed by the anatomist Richard Owen (1849), for all that he was often known as the ‘British Cuvier’. These thinkers pointed to the isomorphisms—now (following Owen) known as ‘homologies’— which exist between organisms, often of very different overall structure and habitat and behaviour. Most famously there are the isomorphisms or homologies existing between the forelimbs of vertebrates of very different kinds (Fig. 2). The bones of the forelimb can be put in one–one correspondence: between the human, who uses the forelimb for grasping; the horse, who uses the forelimb for running; the bat, who uses the forelimb for flying; the bird, who likewise uses the forelimb for flying; the mole, who uses the forelimb for digging; and the whale, who uses the forelimb for swimming. All very different ends, and yet with isomorphisms between the bones. (The complete isomorphism is often not possible, since some bones are missing in some organisms, but there is an essential correspondence.) It is obvious that these isomorphisms or homologies serve no immediate ends. They were therefore explained in terms of underlying structures which exist throughout nature, perhaps indeed connecting the living with the inanimate. Most

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Fig. 2. Homologies between the forelimbs of several vertebrates. Numbers refer to digits. From Dobzhansky et al. (1977, p. 264). Copyright 1977 by W. H. Freeman and Company. Used with permission.

importantly, the more extreme thinkers of this kind were eager to show that the similarities exist not only within the Cuverian categories but perhaps even bridge the most basic of them all, that is to say the embranchements. Notoriously, Geoffroy crossed swords with Cuvier over the possible homologies existing between

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vertebrates and invertebrates (Appel, 1987). It hardly needs saying that, if indeed the Cuverian categories can be breached and crossed over, then the conceptual foundations of the argument against evolution are much weakened. Although it is difficult to quantify these sorts of things, it seems clear that, by the middle of the last century, the direct teleological approach and the challenging transcendentalist approach were both seen as significant aspects of the living world. Perhaps it is fair to say that the tide was starting to run more strongly towards transcendentalism. In the 1830s it is probably true to say—certainly in Britain, and perhaps also in France—that Cuverian teleology held sway. But by the 1850s, with Cuvier now several decades gone, and with the rise of German academic biological science, more and more stress was being put on comparative morphology and on the task of tracing essential isomorphisms between organisms. Certainly, if one looks at the work of a young morphologist like Thomas Henry Huxley (1898), who came to prominence in the 1850s, one finds that there is almost no attention paid to the older Cuverian teleology. But much stress is put on and significance given to the links between different organic forms as manifested by their homological similarities. It is at this point that Darwin enters the scene, publicly, with the Origin of Species (1859). 2. Darwinian Evolutionism Charles Darwin is rightly called the ‘father’ of evolution (Browne, 1995). His great book, the Origin of Species, establishes the fact of evolution once and for all. Drawing on a wide range of organic phenomena—instinct, paleontology, biogeography, morphology, embryology, systematics, and more—Darwin showed that if one supposes a common origin for all organisms living and dead, then one can explain many facts hitherto inexplicable (Fig. 3). Conversely, these facts prove the truth of the overall hypothesis of evolution. Thus, for instance, Darwin drew attention to the ways in which the denizens of oceanic island clusters are often very similar to each other, yet slightly different. He explained these similarities and differences in terms of common descent. Likewise, Darwin drew attention to the roughly progressive nature of the fossil record, explaining this in terms of descent with modification. And, turning to embryology, Darwin was happy to point to the similarities between the embryos of organisms widely different as adults—the dog and the human, for instance—pointing yet again to the fact that their ancestors were one and the same. The fact of evolution gives an immediate explanation of organic isomorphisms or homologies. This is what Darwin, like others, referred to as the ‘unity of type’. ‘By unity of type is meant that fundamental agreement in structure, which we see in organic beings of the same class, and which is quite independent of their habits of life. On my theory, unity of type is explained by unity of descent’ (Darwin, 1859, p. 233). Had Darwin been Thomas Henry Huxley, this would probably have been the end of the matter. The essential aspects of organic nature, homologies,

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Fig. 3. The structure of Darwin’s argument for the fact of evolution. The fact explains and unifies claims made in the subdisciplines (only some of which are shown) which in turn yield the ‘circumstantial evidence’ for the fact itself.

would now have been explained through evolution. The way would now be opened—an opening through which Huxley and his fellow morphologists marched in the 1860s and 1870s—to look at the details of organic construction and to make inferences about the paths of evolution (‘phylogenies’). There would have been little or no reason to push one’s inquiries further. Darwin, however, for all that he published in the late 1850s and had by then made himself a master of comparative morphology through his detailed studies of barnacles, was truly a child of the 1830s: the time when he formulated his basic ideas about evolution. Darwin—a man educated at the University of Cambridge (the home of the great Isaac Newton) and a prote´ge´ of such important thinkers as William Whewell—always took seriously the task of providing a causal explanation in science. Indeed, no doubt hoping to be the Newton of biology, after becoming an evolutionist Darwin searched hard for some causal mechanism akin to a Newtonian gravitational force. As is well known, Darwin eventually found this mechanism late in 1838: natural selection following on from the Malthusian population explosion which is always occurring amongst animals and plants. First, Darwin argued that there will necessarily be a struggle for existence: A struggle for existence inevitably follows from the high rate at which all organic beings tend to increase. Every being, which during its natural lifetime produces sev-

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eral eggs or seeds, must suffer destruction during some period of its life, and during some season or occasional year, otherwise on the principle of geometrical increase, its numbers would quickly become so inordinately great that no country could support the product. Hence, as more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life. It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms; for in this case there can be no artificial increase of food, and no prudential restraint from marriage. (Darwin, 1859, p. 63)

Then, noting that populations of organisms inevitably contain variation, Darwin argued that success in the struggle will be a function of the particular distinctive characteristics owned by the winners. Hence, there will be a natural form of selection or winnowing: Can the principle of selection, which we have seen is so potent in the hands of man, apply in nature? I think we shall see that it can act most effectually... Can it...be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful in some way to each being in the great and complex battle of life, should sometimes occur in the course of thousands of generations? If such do occur, can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable variations and rejection of injurious variations, I call Natural Selection. (Darwin, 1859, pp. 80–1)

The important thing to note about Darwin’s mechanism of natural selection is that not only is it a mechanism which leads to evolutionary change, and hence not only is it a mechanism which leads to an explanation of the unity of type, but it speaks also to organic design or functionality: that very aspect of organic nature highlighted by Cuvier through his doctrine of the conditions of existence. Darwin is explicit on this matter: natural selection promotes ‘adaptations’ like the eye and the hand and all other such characteristics. Darwin stresses that one must go beyond evolution and the unity of type to selection and adaptation or Cuverian teleology. Picking up on a passage quoted earlier: On my theory, unity of type is explained by unity of descent. The expression of conditions of existence, so often insisted on by the illustrious Cuvier, is fully embraced by the principle of natural selection. For natural selection acts by either now adapting the varying parts of each being to its organic and inorganic conditions of life; or by having adapted them during long-past periods of time: the adaptations being aided in some cases by use and disuse, being slightly affected by the direct action of the external conditions of life, and being in all cases subjected to the several laws of growth. Hence, in fact, the law of the Conditions of Existence is the higher law; as it includes, through the inheritance of former adaptations, that of Unity of Type. (Darwin, 1859, p. 233)

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It can be seen here indeed that the unity of type for Darwin, although important, is subsidiary to the conditions of existence or teleology. Although now publishing in 1859, Darwin was forcing biological thought back twenty years to the time when he conceived his theory. Even though Darwin’s great supporters like Huxley were relatively indifferent to Cuverian teleology and to adaptation, Darwin himself stressed its significance. In this, one might therefore say that, whatever Darwin’s theological and other commitments, he was completely committed to the teleologists’ initial premise: organisms are design-like, whatever the ultimate cause of this design. (By the time of the Origin, Darwin had moved from Christian theism to a form of deism. He probably did therefore believe in a Creator who designed, albeit a Creator who executes design through unbroken law, rather than through direct miraculous interference. Later in life, Darwin’s deism faded into a form of agnosticism. This was partly due to the influence of Huxley and partly due to Darwin’s inability to reconcile any kind of god with the pain and evil in the world.) As is well known, from the time of the Origin down to the present the mechanism of natural selection has had a somewhat checkered and varied existence (Bowler, 1984). For many years, selection was dismissed as an insignificant force in nature. Although some made much of selection, notably Alfred Russel Wallace (1905), the co-discoverer of the mechanism, and his close friend Henry Walter Bates (1892), general opinion was much influenced by Huxley and his group, relegating selection to a minor or even miniscule role. It was thought unnecessary and in any case deemed ineffective. This more or less continued to be the case, with some notable exceptions (for instance the ardent Oxford evolutionists Raphael Weldon and Edward Poulton), until the 1930s. Then selection came into its own, thanks first to the work of the genetical mathematical theorists R. A. Fisher, J. B. S. Haldane and Sewall Wright, and then second to the empiricists like the Russianborn American geneticist Theodosius Dobzhansky, and the British entomologist and ecologist E. B. Ford (Ruse, 1996). A hundred years after the Origin, at the time of the centenary in 1959, selection seemed fully secure: the major mechanism of evolutionary change. And in respects it has retained this status, especially in those quarters interested in such issues as social behaviour. Thanks to the work of theoretical sociobiologists such as William Hamilton (1964a,b) and John Maynard Smith (1982), and their empiricist followers such as Nicholas Davies (1992) and Geoffrey Parker (1978), natural selection continues today to be an absolutely crucial tool in dissecting evolutionary aspects of the organic world. However, notoriously, in the past two or three decades considerable opposition has again started to rise against selection. This attack is spearheaded particularly by American paleontologists and geneticists, notably Stephen Jay Gould and Richard C. Lewontin (1978). It is claimed that selection is much overpraised, and that perhaps we ought to revert more to a Germanic-type understanding of evolution: an understanding where the unity of type again takes precedence over the conditions of existence. The key term here is that of ‘Bauplan,’ a German term

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meaning groundplan or blueprint: what pre-Darwinian English evolutionists used to call the ‘archetype’, meaning the non-adaptive structure on which the organism was based and from which all homologous parts are modeled. In continental Europe, evolutionists have never been much attracted to the AngloAmerican penchant for atomizing organisms into parts and trying to explain each as a direct adaptation. Their general alternative... acknowledges conventional selection for superficial modifications of the Bauplan. It also denies that the adaptationist programme (atomization plus optimizing selection on parts) can do much to explain Baupla¨ne and the transitions between them. But it does not therefore resort to a fundamentally unknown process. It holds that the basic body plans of organisms are so integrated and so replete with constraints upon adaptation... that conventional styles of selective arguments can explain little of interest about them. It does not deny that change, when it occurs, may be mediated by natural selection, but it holds that constraints restrict possible paths and modes of change so strongly that the constraints themselves become much the most interesting aspect of evolution. (Gould and Lewontin, 1979, p. 265).

Putting matters in the terms of our discussion, we can say simply that the important issue for Darwin, and for evolutionists from Darwin down to the present, has been that of organic teleology. Those evolutionary biologists who agree with Darwin (and with Cuvier before him) think that the distinctive mark of the organic world is its forward-looking functionality. Organisms are adapted, hence they are teleological, and (for the Darwinian) this teleology can be explained through, and only through, natural selection. Consider the writings of today’s most ardent Darwinian: Richard Dawkins. He argues that the mark of the living is its teleological nature, and that such teleology can be explained only through natural selection. No other mechanism will do. The key to the Darwinian explanation of adaptive complexity is the replacement of instantaneous, coincidental, multi-dimensional luck, by gradual, inch by inch, smeared-out luck. Luck is involved, to be sure. But a theory that bunches the luck up into major steps is more incredible than a theory that spreads the luck out in small stages. This leads to the following general principle of universal biology. Wherever in the universe adaptive complexity shall be found, it will have come into being gradually through a series of small alterations, never through large and sudden increments in adaptive complexity. (Dawkins, 1983, p. 412)

All the putative evolutionary rivals to natural selection which address adaptation— notably the venerable belief in the inheritance of acquired characteristics, so call ‘Lamarckism’—are known to be false. So it is natural selection or nothing. My general point is that there is one limiting constraint upon all speculations about life in the universe. If a life-form displays adaptive complexity, it must possess an evolutionary mechanism capable of generating adaptive complexity. However diverse evolutionary mechanisms may be, if there is no other generalization that can be made

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about life all around the Universe, I am betting that it will always be recognizable as Darwinian life. The Darwinian Law... may be as universal as the great laws of physics. (Dawkins, 1983, p. 423)

On the other hand, those biologists—notably Gould and Lewontin—who deny that selection has such a major role to play are precisely those who fail to see Cuverian teleology writ large through the organic world. As we saw, these are biologists under the influence of a kind of neo-Naturphilosophie: they see homologies and their underlying patterns (so-called Baupla¨ne) as the distinctive feature of the organic world. In this discussion, it is perhaps not for me to judge whether today’s Darwinians have the better of the argument over the critics. I am an ardent partisan in the camp of Darwinism, seeing teleology and design nigh everywhere (Ruse, 1982). I make even Cuvier look weak-kneed! Hence, I will simply conclude this section by stressing that, for the Darwinian, Cuverian-type teleology is an absolutely crucial fact of the organic world and one deeply in need of explanation. Such explanation comes through and probably only through natural selection. For the critics, Cuverian teleology is nowhere near as wide-spread and significant as its enthusiasts claim. For them, therefore, although selection undoubtedly plays some role in the evolutionary origins of organic nature, it would be a grave mistake to overemphasize the significance of this role. There are other factors are work. Perhaps, since the overriding characteristic of organic nature is homology, it is enough to stress the fact of evolution. Actual causes are less significant, and may indeed be little more than randomness or chance, rather than something of a consistent, directed nature. 3. Looking Forward We come now to our final question—What is the true nature and status of biological teleology?—and we ask this question with an eye to teleology’s future role and prospects in evolutionary thought. Let me start by acknowledging that there are many who regret evolutionary biology’s teleological cast. They think that, even though natural selection may well have a role to play in biological thought, teleology itself is an unfortunate relic of pre-evolutionary Christian thought, or worse. (For some peculiar reason, in the eyes of many biologists, ‘worse’ usually refers to Greek thinkers, notably Plato and Aristotle. I will not stop here to dig more deeply into the sources of this very strange illusion.) Typical of teleology’s naysayers is the following editorial in a popular biological journal Some writers seem to regard the use of teleological terminology such as ‘striving to attain goals’ as a way of catching the reader’s attention. Others apparently use it metaphorically as a convenient method of examining problems. However, it is dangerous because it results in careless thinking and writing, and it misleads readers not

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trained in science who often mistake the metaphor for the truth. A humanist acquaintance... suggested a warning that ‘The attribution of purpose to plants is not intended literally, and if so taken is dangerous to your mental health’. Scientists can have goals and can develop research strategies to attain them, but plants cannot, unless we are willing to grant that they have intelligence and can make decisions. Terms such as ‘strategy’ and ‘tactics’ are philosophically objectionable when applied to plants and lower animals, and are best left to politicians, the military, and athletic coaches. (Kramer, 1984, in Ruse, 1988, p. 186)

But is it going to be quite as easy to eliminate teleology as this writer supposes? And even if such teleology could be eliminated, would this be entirely a good thing? Probably the answer to this question depends in major part on how much would be involved in the job of elimination. If it could be done readily and without too much disruption, then why not remove it? And, in pursuit of such a goal, let me note that many philosophers have thought that the task of removal was reasonably straightforward. Much impressed by the development of homing or goal-directed devices in the Second World War—the rocket or submarine or missile which could respond to a moving target and redirect itself accordingly—in the 1950s and the 1960s, it was popularly thought that here we have the key to an understanding and possible removal of evolutionary teleology. The noted logical empiricist Ernest Nagel (1961) argued that whenever biologists speak in terms of functions, or purposes, or ends or design, they are referring silently to systems which are goaldirected, or (as he put it) ‘directively organized’. This and this alone is the import and content of biological teleology. Thus, if one is prepared to acknowledge that organisms are goal-directed, and if one is perhaps prepared also to spell out the ways in which such goal-directedness operates, the elimination of teleology from evolutionary biology should be a fairly straightforward matter. However, these optimistic suggestions and proposals have since been shown to be less than entirely convincing. As was pointed out by the late C. H. Waddington (1957), people such as Nagel are confusing two similar-sounding, but somewhat different, biological notions: ‘adaptability’ and ‘adaptedness’. To say that an organism is ‘adaptable’ is to say truly that it is goal-directed or directively organized in a Nagelian sense. It is to say that, if something occurs, the organism can in some way bring itself back on track. A paradigm instance is shivering and sweating in the mammal: activities which are designed to return an overheated or overcooled organism to its desired, constant, internal temperature. But, note that to say that an organism is ‘adaptable’ is not in itself to say that an organism is ‘adapted’, or conversely. It is undoubtedly true that just about every organism is going to be adaptable in some sense or another, and also any successful organism must be adapted. However, if an organism is well-adapted, in this particular respect it may well have no scope for response at all. To say, for instance, that because of its white fur coat the polar bear is well-adapted to an arctic life, is not in any sense to say that, should global warming eliminate most of the arctic ice and snow, the polar bear could then immediately respond by turning brown or some other more

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useful colour. It could well be that polar bears would go extinct, because they were unable to change. Adaptedness does not spell adaptability, and conversely, one can readily think of instances where something may well be adaptable, in the sense of able to respond to change, and yet the organism would be in a better state if it were to stick things out through minor environmental fluctuations without changing. Unfortunately for the biology-teleology-eliminators, as we have seen, the teleology of biology—focused as it is on natural selection—refers to adaptedness not to adaptabililty. To say that the polar bear’s coat colour serves the end of survival and reproduction of its owner—that the whiteness exists in order to promote polar bear well-being—is to say that the coat colour is an adaptation. In addition, it is to point out that polar bears were in some sense selected for their habitat: that those who were less than white failed to survive and reproduce as efficiently as those who were. Nothing here is being said about adaptability. Hence, one has to conclude that, although indeed polar bears are probably adaptable, inasmuch as one is thinking of them teleologically, one is not referring to this particular aspect of their nature. One is returned then to the whole question of adaptiveness. And let us note that what we have here is a metaphor: organisms are being treated as if they were designed (Ruse, 1989). One might in fact think that they are designed, by the Great Designer in the Sky. But the point here is that, whether or not God stands behind the design-like nature of organisms, inasmuch as one is doing biology one is simply treating organisms as if they were designed. To use another memorable metaphor, namely that of Richard Dawkins (1986), qua biologist one is assuming that a ‘blind watchmaker’ has been at work rather than a conscious intelligence. The metaphor in play here is that of a human-constructed artifact or object. A pair of scissors, for instance, is designed by humans: it has an intentionality and teleology, because we confer such intentionality upon it. The scissors exist in order to cut, because that is our desire. The forward-looking nature of scissors comes, not from causes operating out of the future or anything like that, or even in a sense from something inherently in the scissors themselves, but rather from human intentions. Intentions which we have now, but which refer to events which we hope will obtain in the future. (As a number of people have pointed out, it is important to stress that the hope is that the events will obtain in the future, not that they will obtain. Otherwise one gets caught with the so-called ‘missing goal object problem’, where one is assuming that things are being affected by future events which may not occur. The scissors may never be used for cutting, because they get lost shortly after purchase.) The whole point about organisms is that, inasmuch as we are thinking of them teleologically, we are thinking of them as objects of design. This is the reason why teleological language seems appropriate in the organic world, but not elsewhere. Rocks and planets and moons and the like just simply do not seem as if designed. However, the fins on the back of the Stegosaurus do seem as if they were consciously planned (Fig. 4). As biologists have pointed out, they are very similar to

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Fig. 4. Stegosaurus, a large herbivorous dinosaur of the Jurassic period, had an array of bony plates along its back. Were they a solution to the problems of defence, courtship recognition or heat regulation? An engineering analysis reveals features characteristic of heat regulation: porous structure (suggesting a rich blood supply), particularly large plates over the massive part of the body, staggered arrangement along the midline, a constriction near the base, and so on. This skeleton in the American Museum of Natural History is 5.5 m long. From Lewontin (1978, p. 217). Reprinted with the permission of the estate of Bunji Tegawa.

the fins that one finds on heat-exchange mechanisms surrounding electrical generators. For this reason one is happy to talk about the function, or end, or purpose of the Stegosaurus’ back adornments. As in generators, the fins exist in order to promote heat exchange. They are like human artifacts and so, as in the case of real artifacts, teleological language is appropriate. Likewise, to use my own favourite example, the eyes of the trilobite (Fig. 5) are made with two lenses to correct for chromatic aberration, just as Descartes and Huygens worked out (Fig. 6) some five hundred million years after those particular invertebrates flourished (Clarkson and Levi-Setti, 1975). Having stressed the fact that we have here a metaphor, is this not also the clue as to why now such teleology might at least in principle be eliminable? Many would argue that, although metaphors do indeed occur frequently in science, in some important sense they are dispensable: indeed, the mark of a mature science is that metaphors can be and are so eliminated. As Jerry Fodor (1996) has said, when science gets serious metaphors go out and mathematics comes in. I suspect that, if one were so determined, in principle one could eliminate the metaphors of science. At least, let me speak in a more restricted way and say that, if one were determined, I suspect that one could in principle eliminate the metaphor of design from evolutionary biology. One could have an evolutionary biology which spoke not at all in teleological language. At the most drastic, one would simply refuse to consider questions of functionality at all. One would concentrate— in a kind of exaggerated parody of Gould and Lewontin—exclusively on such

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Fig. 5. Trilobites are long-extinct marine invertebrates whose ecological niche is today taken by crabs and like creatures. They had very complex eyes using a large number of lenses. This is a much magnified photograph of such a trilobite eye. From Clarkson and Levi-Setti (1975, p. 663). Reprinted with permission of the authors. Copyright Nature.

issues as homology and the consequent unity of type. (In real life, I agree that Gould and Lewontin do acknowledge some degree of adaptation.) Somewhat less drastically, I suspect that if one were determined, one could even look at adaptations—the eye and the hand—and refuse to think teleologically. One could characterize natural selection simply in terms of a differential reproduction, pointing exclusively to what has happened in the past. Thus, in speaking of the fins of the Stegosaurus, one would ask not what purpose or function these fins play. One would simply talk in terms of past events. One would say that those Stegosauri with more and more diamond-like-shaped fins were those that survived and reproduced, and those which did not have such fins did not. One could even go on to say precisely why it was that the successful Stegosauri survived and reproduced: the more diamond-like fins acted as efficient heat transfers, whereas those less diamond shaped acted as less efficient heat transfers. There was a consequent differential reproduction of the respective possessors. And the same is true of other organisms, like the trilobites. But note, even here, how limited or truncated one’s thinking is. One is able to provide the non-teleological explanation about heat transference only because one knows this to be the answer already! The question I ask—the question that evolutionary biologists ask—is how did one know in the first place that the fins would

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Fig. 6. How does one design a lens which avoids spherical aberration? In the seventeenth century, Rene´ Descartes (upper left) and Christian Huygens (upper right) discovered the shape of the required lenses. However, as the lower diagrams (cross-sections of two trilobite eyes) show, nature had beaten them by a long time. The trilobite intralensar bowls are needed for sharp focusing because trilobite eyes functioned in water. From Clarkson and Levi-Setti (1975, p. 665) Reprinted with permission of the authors. Copyright Nature.

or would not be efficient for heat transference? The answer of course is because one has being relying on the metaphor of design! Precisely because one has being thinking of the Stegosaurus’ parts as artifacts, that is to say as objects of conscious intention, one has been able to ferret out in which ways they work. In which ways they work as objects of intention. Precisely because one is thinking of the trilobite eye lenses as if designed and created by a real optician, can one find out why they are as they are and how they worked. One might now drop the metaphor-like talk, but remember one has had it and relied on it in the first place. One is not doing without it: one is simply not acknowledging it. My point therefore is that this kind of elimination of teleology is all a little bit bogus. One is using a sleight of hand. First, one uses the metaphor with all of its teleological implications. Then second, when once one has achieved the ends one desires, one drops the metaphor like an unwanted spouse and one pretends that one never had anything to do with it all. The children of the union are there for one to claim for one’s own, and the former partner is locked out entirely. But

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although one might be able to get away with this socially (less so these days of course), intellectually, in the scientific realm, this is illicit. At best shady practice in the cause of a dubious philosophical thesis. Even one’s finished formal theory makes no direct reference to the metaphor of design, and thus eliminates the teleology, even though in order to achieve the end results one has had to use the metaphor with all of the teleological implications that it carries. No one is going to be able to say why those Stegosaurus fins exist and in what form without the metaphor. Note what is going on here. The metaphor of design is being used as an essential heuristic guide in evolutionary biology: precisely the role that students of metaphor always attribute to such modes of thinking (Ruse, 1999). Whether or not metaphors are an essential part of theories, they are absolutely essential for the production of such theories (Hesse, 1966). Inasmuch as one’s scientific theory—in our case evolutionary biology—is heuristically powerful, or in other language has the epistemic virtue of fertility, one is relying heavily on metaphor—in our case, the metaphor of design. Because, and only because, evolutionary biologists think of organisms as if they were humanly-made artifacts can they produce answers to questions about the ways in which these organisms survive and reproduce; that is to say, can they produce answers about the ways in which natural selection functions in the organic world. Of course, you may want to argue that functionality has been overdone in evolutionary biology. This is a matter which has been discussed already in this paper, and is one that I have laid on one side. For myself, as with other Darwinians, I regard functionality to be the absolutely central feature of life. Even if one denies this centrality, one must still agree that functionality has some role to play in our understanding of organic life and of its change. Even critics like Gould and Lewontin admit this much. Hence, I would argue that because such functionality is an important aspect of organic nature and because it is produced by natural selection, the metaphor of design is here to stay and should be recognized fully for what it is. In other words, what I argue is that, however wrong Cuvier may have been about teleology precluding evolution, he was surely right in arguing that an essential aspect of organic nature is its forward-looking cast. I have never been entirely convinced by Foucault’s clever claim that evolutionary biology owes more to Cuvier than to Lamarck, but there is surely some truth in it (Foucault, 1970). 4. Conclusion Biological teleology is something which predates evolutionary thought. It was taken over by evolutionists, particularly by Charles Darwin in his Origin of Species because the problems it addressed exist as much for the evolutionist as they do for the nonevolutionist. In particular, organisms seem as if designed; they are adapted, and this calls for explanation. It is for this reason that teleological thought is appropriate in the biological sciences; and because nonorganisms do not seem

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as if designed, teleological thought is inappropriate in the nonbiological, physical sciences. Post-Darwin, teleological thought is intimately connected with natural selection, and this explains why even today there is a divide between evolutionists on the matter of teleology. Those who follow Darwin think that adaptation is of crucial importance: therefore, they champion natural selection, and cherish teleological thinking. Those who do not follow Darwin deny the great significance of adaptation: they are less enthused by natural selection and they are less enamored by teleological thought. Philosophically speaking, perhaps in principle teleology can be eliminated from biological thought, even from evolutionary biological thought. But to do so would be to cut off interesting and surely important areas of inquiry. Teleology depends on a metaphor and as with all scientific metaphors this is the secret to science’s heuristic power, to its predictive fertility. It is for this reason that the teleology of evolutionary biology is surely here to stay and might be expected to flourish in the future. In a sense, therefore, although the coming of evolutionary biology, particularly the coming of Darwinian evolutionary biology, was the most important thing ever to happen to the biological sciences, its particular significance lies in its giving new answers to old questions, rather than in always asking entirely new questions. Teleology: yesterday, today, and tomorrow! References Appel, T. A. (1987) The Cuvier-Geoffroy Debate: French Biology in the Decades Before Darwin (New York: Oxford University Press). Bates, H. W. (1892) The Naturalist on the River Amazon (London: John Murray; first published in 1863). Bowler, P. (1984) Evolution: The History of an Idea (Berkeley: University of California Press). Browne, J. (1995) Charles Darwin: Voyaging. Volume 1 of a Biography (New York: Knopf). Chambers, R. (1844) Vestiges of the Natural History of Creation (London: Churchill). Clarkson, E. N. K. and Levi-Setti, R. (1975) ‘Trilobite Eyes and the Optics of Descartes and Huygens’, Nature 254, 663–67. Coleman, W. (1964) Georges Cuvier, Zoologist: A Study in the History of Evolution Theory (Cambridge, MA: Harvard University Press). Cuvier, G. (1813) Essay on the Theory of the Earth, trans. R. Kerr (Edinburgh: W. Blackwood). Cuvier, G. (1817) Le re`gne animal distribue´ d’apre´s son organisation, pour servir de base a` l’histoire naturelle des animaux et d’introduction a` l’anatomie compare´e (Paris: Deterville). Cuvier, G. (1830) ‘Conside´rations sur les Mollusques, et en particulier sur les Ce´phalopodes’, Annales des sciences naturelles 19, 241–359. Darwin, C. (1859) On the Origin of Species (London: John Murray). Davies, N. B. (1992) Dunnock Behaviour and Social Evolution (Oxford: Oxford University Press). Dawkins, R. (1983) ‘Universal Darwinism’, in D. S. Bendall (ed.) Molecules to Men (Cambridge: Cambridge University Press) pp. 403–25. Dawkins, R. (1986) The Blind Watchmaker (New York: Norton). Dobzhansky, T., Ayala, F. J., Stebbins, G. L. and Valentine, J. W. (1977) Evolution (San Francisco: W. H. Freeman).

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