Monday, April 28, 2008
Even Tierra del Fuegans Do It
The Uncashed Metaphor of Natural Selection
Justin E. H. Smith
In their classic 1979 article, "The Spandrels of San Marco and the Panglossian Paradigm," Stephen Jay Gould and Richard Lewontin fault the adaptationist program for its failure to distinguish current utility from reasons for origin; its unwillingness to consider alternatives to adaptive stories; its reliance upon plausibility alone as a criterion for accepting speculative tales, and, as they put it, for "its failure to consider adequately such competing themes as random fixation of alleles, production of non-adaptive structures by developmental correlation with selected features… the separability of adaptation and selection, multiple adaptive peaks, and current utility as an epiphenomenon of nonadaptive structures." They announce that in the critique they are offering, they are proceeding in the spirit of "Darwin's own pluralistic approach to identifying the agents of evolutionary change."
Spandrels, or the tapering triangular spaces formed by the intersection of two rounded arches at right angles, are, as they explain, "necessary architectural byproducts of mounting a dome on rounded arches." In other words, you can't have an arch without a spandrel, and you need an arch in order to support a roof. If you ask the architect why he put the spandrel there, he will tell you you don't understand architecture.
Gould and Lewontin believe that this architectural example has much to tell us about biological evolution. In particular, they believe that many of our efforts to account for some given trait of an organism as having been selected-for is a futile project: it is often the case that traits were never selected at all by environmental pressures, but only came into being, like the spandrels, as 'free-riders' on the traits that these pressures in fact selected. The beautiful paintings that cover the spandrels are in turn the architectural analogue of exaptations, that is, features that were never selected-for, but once having come into existence as free-riders on different selected-for traits, turn out to have some fortuitous utility.
How do we know which traits of an animal are like the arches, and which like the spandrels? This might be harder to determine than Gould and Lewontin's predecessors had thought, but the difficulty only means that greater attention should be played to the role that the Bauplan of the integrated whole plays in evolution, not that natural selection as such should be rejected.
Jerry Fodor in contrast --in several books, including The Mind Doesn't Work That Way (his response to Steven Pinker's How the Mind Works), as well as in a fiery polemic with Simon Blackburn, Philip Kitcher, Dan Dennett and others in several recent issues of the London Review of Books-- wants to say that since any trait is always coextensive with another, it is impossible to say which of the two (or more) was the one that was selected-for. This is not in his view an epistemological problem, but an ontological one: the problem is not that we cannot know which trait was selected, but that it is meaningless to talk about the one or the other being the trait that was selected. It's all spandrels, and it's all arches, and there's no architect we might ask to help us tell the difference. Fodor writes:
"Getting minds in general, and God's mind in particular, out of biological explanations is a main goal of the adaptationist programme. I am, myself, all in favour of that; since I'm pretty sure that neither exists, I see nothing much to choose between God and Mother Nature. Maybe one can, after all, make sense of mindless environmental variables selecting for phenotypic traits. That is, maybe one can get away with claiming that phenotypes are like arches in that both are designed objects. The crucial test is whether one's pet theory can distinguish between selection for trait A and selection for trait B when A and B are coextensive: were polar bears selected for being white or for matching their environment? Search me; and search any kind of adaptationism I've heard of. Nor am I holding my breath till one comes along."
The consensus among Fodor's critics is that he has systematically misunderstood the point of Gould and Lewontin's argument. My own impression is that his argument is either irresponsible and stupid or so subtle that none of his adversaries, defending a status quo interpretation of the theory of natural selection, have been able to get it yet. The principle of charity pushes in favor of the latter view.
What Fodor wants to know is whether the polar bear's coat was selected-for because it's white or because it matches its environment. According to Blackburn et al., the familiar adaptationist account, which they do not see as in need of revising, would have it that "[i]n some ancestral population there was a variant type that differed from the rest in ways that enhanced reproductive success. (White polar bears, for example, more camouflaged than their brown confrères, were better at sneaking up on seals, were better fed and left more offspring.) If the variant has a genetic basis, its frequency increases in the next generation." For Fodor however, this is a "potted polar bear history," since "for any trait X that was locally coextensive with being white in the polar bear’s evolutionary ecology[, s]election theory is indifferent between ‘the bears were selected for being white’ and ‘the bears were selected for being X.’" A good theory, Fodor thinks, should be able to generalize over possible but non-actual circumstances, that is, it should be able to support relevant counterfactuals, and this is something that natural selection doesn't do.
If you are not satisfied with the polar bear story, Fodor also offers a well-known example from the real world: in a certain variety of foxes, whenever they are bred (by humans) for tameness, the offspring come out not only tame, but also floppy-- floppy ears, floppy tails, etc. These are ancillary effects that are observed in many species of domesticated animal, and they are much harder to account for, Fodor thinks, than the fit between arches and spandrels, since the connection between tameness and floppiness is, he thinks, perfectly arbitrary. (Actually, I can think of a perfectly plausible potted story as to why floppiness and tameness go together: it is advantageous to a domestic animal to be cute; roundness and softness are more likely to get a domestic animal to reproductive age than jaggedness, prickliness, and other visible vestiges of its feral past.)
Fodor seems to have failed to note that in each of the three cases in question --the spandrels, the whiteness, and the floppiness--, at least three different kinds of coextensiveness seem to be in play. In the first, we are dealing with two traits that are non-identical but logically coextensive; in the second, with two traits that are in-this-world identical even if they support different counterfactuals; and in the third, with two non-identical and contingently linked traits. It could have been the case that the gene for floppy ears be located somewhere such that breeding for tameness would have yielded tame, pointy-eared foxes, but there is no possible scenario in which brown bears could have matched their snowy environment, even if counterfactually they could have had a non-snowy environment, and all this for reasons having nothing to do with genetics.
In the case of the polar bear, the traits are not entirely identical, since again, as Fodor puts it, being white and blending with the environment support different counterfactuals. The environment could have been orange. So it is not that coextensive properties are indistinguishable in principle, but only that there is something wrong with natural selection to the extent that it fails to distinguish between them. Yet, one might reply to Fodor, environmental pressures do not operate on counterfactual states of affairs, only on the actual one, and in the actual one no decision had to be made as between whiteness and blending. In the sort of counterfactual, experimental situation Fodor imagines --such as painting all the snow orange--, the decider would be whoever set up the experiment, and not nature. So we seem either to have an identity of coextensive traits, or we have human agency, in which case there is a fact of the matter as to which of the two coextensive traits was selected. We will return to this point shortly.
Fodor has certainly been right to draw inspiration from Gould and Lewontin's argument in his crusade against the rampant plague of just-so stories that one hears from evolutionary psychologists. This crowd often assumes that what homo sapiens is in its essence is a hunting-and-gathering species, and that therefore whatever it is that we do must have some adaptive explanation as being somehow beneficial for hunter-gatherers. The result is often a caricaturing of human behavior of the most transparently Flintstones variety.
Gould and Lewontin however did not want to reject adaptation tout court, but only the view that every trait must be accounted for in terms of selection-for. How though do we distinguish the traits that may be accounted for in this way? Blackburn et al. appear to want to say that it is just obvious, while Fodor responds that it never is. A moderate balance of these two approaches would be to hold that adaptationism seeks to offer plausible accounts, based on counterfactuals, of what selection pressures would have to have enabled to come into existence so that the currently existing species might persist in existence. Certainly, a different standard will be brought to bear here than in laboratory science --plausibility rather than falsifiability-- but what other choice do we have? Fodor's ahistorical approach to the philosophy of mind seems to lead him to the rather extreme view that the past must remain off limits to science because it demands a different methodology than the most secure and unproblematic disciplines, such as aerodynamics, that he habitually holds up as models for his own domain of inquiry.
It is, again, interesting to note that the one really useful example of coextensiveness of traits in the biological world comes from an example in which human beings --fox breeding scientists, in the event-- are making the decisions, just like the cathedral's architects. There is a way to distinguish, not just in principle but in fact, which of the two vulpine traits in question was selected, since it was humans who were doing the selecting. Indeed, one of Fodor's arguments for the incoherence of the adaptationist program, an argument in my view more compelling than the argument from the lack of support of relevant counterfactuals, points out that not just in the case of the foxes and the polar bears, but with respect to all observed traits we can only arrive at a secure understanding of what was selected-for when we are able to interrogate the selecter. This is of course something we are never able to do in non-experimental cases, and so, for Fodor, any talk of natural selection is strictly metaphorical, and a great problem with Darwinism is that it never gave us any instruction as to how to translate this metaphor into a proper scientific account of things.
Fodor claims that history is not relevant to the philosophy of mind, but in the end relies on historical considerations much more than he himself notices, admittedly not concerning the evolution of species, but concerning the history of Victorian natural history, and Darwin's place in it. He writes:
"[T]he present worry is that the explication of natural selection by appeal to selective breeding is seriously misleading, and that it thoroughly misled Darwin. Because breeders have minds, there's a fact of the matter about what traits they breed for; if you want to know, just ask them. Natural selection, by contrast, is mindless; it acts without malice aforethought. That strains the analogy between natural selection and breeding, perhaps to the breaking point. What, then, is the intended interpretation when one speaks of natural selection? The question is wide open as of this writing."
Given that nature lacks a mind, it, or its environmental pressures, can't really 'select' anything, any more than the ball in a roulette machine can select a color to land on. Metaphors are fine things, Fodor acknowledges, and "science probably couldn't be done without them." But they are supposed to be the sort of things, he thinks, "that can, in a pinch, be cashed. Lacking a serious and literal construal of 'selection for', adaptationism founders on this methodological truism."
Fodor is absolutely right, and not just about the current Darwinist orthodoxy, but about the historical Darwin himself, who explicitly borrowed the notion of selection from the domain of animal husbandry, and left it to his followers to cash the metaphor. Few before Fodor have noticed just how problematic is the legacy that Darwin has bequeathed: on the one hand, a thorough-going naturalism about how animals come to have the traits they have, and on the other hand a fairly blatant personification of nature as breeder.
Surprisingly, Fodor's critique of natural selection on this point echoes in important ways certain pre-Darwinian arguments against natural theology, that is, against the view that God's wisdom can be discerned in the order of nature. Most early modern natural theology took it for granted that the relation that God bore to his orderly creation was something very like that of a machinist to his machine. In the Dialogues on Natural Religion, Hume has the natural theologian Cleanthes declare:
"Look around the world: Contemplate the whole and every part of it: You will find it to be nothing but one great machine, subdivided into an infinite number of lesser machines… All these various machines, and even their most minute parts, are adjusted to each other with an accuracy, which ravishes into admiration all men, who have ever contemplated them. The curious adapting of means to ends, exceeds the productions of human contrivance; of human design, thought, wisdom, and intelligence. Since, therefore the effects resemble each other, we are led to infer, by all the rules of analogy, that the causes also resemble; and that the Author of nature is somewhat similar to the mind of man; though possessed of much larger faculties, proportioned to the grandeur of the work, which he has executed."
Hume, in the guise of Philo, proffers several arguments in reply to Cleanthes, but certainly the one most relevant for our purposes is the argument from the incomplete analogy at the heart of natural theology: because of our experience with artefacts and their artisans, we can tell the difference between artefacts and natural objects, and give an account of how the former sort of thing came into being. But in order to properly pick out a designed universe, we would need to have an experience of that universe's maker, which we obviously don't have. If you find a watch in the forest, then you are entitled to infer to the existence of a watchmaker, but only because you already know quite a bit about not just watches but also about watchmakers themselves: you can go, and may already have gone, to check out their workshops and examine their tools. But in the case of the world, we only know the 'watch', and come to think of it, Philo muses, there is nothing particularly watch-like about this particular world. In fact, notwithstanding the fashion for the watch-world analogy that had found such eloquent defenders in Boyle, Newton, et al., Hume prefers to return to a much more ancient and deeply rooted vision of the cosmos as, in Aristotelian terms, a natural being rather than as an artefact:
"Now, if we survey the universe, so far as it falls under our knowledge, it bears a great resemblance to an animal or organized body, and seems actuated with a like principle of life and motion. A continual circulation of matter in it produces no disorder: a continual waste in every part is incessantly repaired: the closest sympathy is perceived throughout the entire system: and each part or member, in performing its proper offices, operates both to its own preservation and to that of the whole. The world, therefore, I infer, is an animal; and the Deity is the SOUL of the world, actuating it, and actuated by it."
One of the important implications of such a cosmological model, Philo soon realizes, is that it compels us to think of the order in the world not so much as made, but rather as generated:
"[I]n examining the ancient system of the soul of the world, there strikes me, all on a sudden, a new idea, which, if just, must go near to subvert all your reasoning, and destroy even your first inferences, on which you repose such confidence. If the universe bears a greater likeness to animal bodies and to vegetables, than to the works of human art, it is more probable that its cause resembles the cause of the former than that of the latter, and its origin ought rather to be ascribed to generation or vegetation, than to reason or design."
The design of the world, in short, is more like a physiological process than a mechanical one. It is not that it does not have order or design, but only that this does not come from a machinist. It comes from a progenitor.
Hume's rejection of the argument from design is connected, one might argue, as much with the decline of the 17th-century mechanical model of nature as it is with the skeptical concern about the incompleteness of the watchmaker analogy. A world-machine would need a maker, but a world-animal could in principle be immortal, as it had been for Plato and later for the Stoics. What we need to consider, then, in order to understand the continuities and discontinuities between natural theology and natural selection, is precisely the ontological difference between artefacts and natural beings, which at once dictates the degree of control the 'designer', whether mortal or divine, may have in each of the two cases. Most significantly, natural machines can at most be sculpted by environmental forces or by intervention; they cannot be brought into being in the first place.
In this connection, on the reading of Darwin I shall proceed to sketch out, natural selection isn't so much a shift from theological thinking about design in nature, as it is a demotion of the designer from the role of creator to the role of modifier, and from the relatively prestigious role, one might add, of inventor, to the relatively humble job of animal breeder.
In the opening pages of his 1859 masterwork On the Origin of Species, Darwin praises the expert knowledge and artisan's skill of domestic pigeon breeders. Their expertise, Darwin thinks, lies in their ability to discern barely visible traits and to amplify them over the course of generations by selecting appropriate mates for the pigeons who display them. "The key is man's power of accumulative selection," Darwin writes, "nature gives successive variations; man adds them up in certain directions useful to him. In this sense he may be said to make for himself useful breeds." Darwin goes on to praise the great skill of England's finest breeders, who, while admittedly working with pregiven Baupläne, are able to achieve results comparable to those of a divine creator:
"Breeders habitually speak of an animal's organisation as something quite plastic, which they can model almost as they please. If I had space I could quote numerous passages to this effect from highly competent authorities. Youatt, who was probably better acquainted with the works of agriculturalists than almost any other individual, and who was himself a very good judge of an animal, speaks of the principle of selection as 'that which enables the agriculturist, not only to modify the character of his flock, but to change it altogether. It is the magician's wand, by means of which he may summon into life whatever form and mould he pleases.' Lord Somerville, speaking of what breeders have done for sheep, says: 'It would seem as if they had chalked out upon a wall a form perfect in itself, and then had given it existence.'" [Italics added].
While Darwin is impressed by the way in which some skilled breeders of pigeons and other domestic species choose to summon into life new forms, he is just as interested in the way in which domestication has led to the emergence of new and unforeseen traits in animals and plants. This is the result, Darwin thinks, of a sort of 'unconscious' selection on the part of the human masters of domesticated animals:
"At the present time, eminent breeders try by methodical selection, with a distinct object in view, to make a new strain or sub-breed, superior to anything existing in the country. But, for our purpose, a kind of Selection, which may be called Unconscious, and which results from every one trying to possess and breed from the best individual animals, is more important."
Darwin repeatedly mentions that 'even savages' grasp the basic principles of selection. "If there exist savages so barbarous as never to think of the inherited character of the offspring of their domestic animals," Darwin observes,
"yet any one animal particularly useful to them, for any special purpose, would be carefully preserved during famines and other accidents, to which savages are so liable, and such choice animals would thus generally leave more offspring than the inferior ones; so that in this case there would be a kind of unconscious selection going on. We see the value set on animals even by the barbarians of Tierra del Fuego, by their killing and devouring their old women, in times of dearth, as of less value than their dogs."
Why does this supposed practice of the Yaghan matter to him? Darwin seems to think that "savages" provide the sort of low-level, unconscious guidance of the breeding of animals for preferred traits that even more closely approximates the guidance provided by nature than, say, the highly developed science of animal breeding described by Youatt, Somerville, et al. Nature is in short the ultimate savage: though herself uncultivated, she can't help but cultivate. Her selections are not like the conscious moulding of new races by England's finest breeders. But neither are they totally unlike this either. They are rather a low-level, mind-like force guiding the emergence of orderly forms.
Even in the case of England's expert breeders, the creative capacity involved is rather less than that of the artificer. "Man can hardly select," Darwin notes, "any deviation of structure excepting such as is externally visible; and indeed he rarely cares for what is internal. He can never act by selection, excepting on variations which are first given to him in some slight degree by nature." Selection, then, involves in all cases less of the creative power of transferring an envisioned form into matter than had earlier been imagined in the model of nature as machine and God as machinist. The selections a savage makes, moreover, involve less conscious imposition of an envisioned form than the selections of a master breeder, and nature's selections even less still. Selecting, unlike making, has to proceed with some pregiven thing, within the limitations dictated by its preexisting Bauplan.
Darwin's 'Mother Nature' then, as Fodor understands it, even if a theological hold-out or a metaphor still in need of cashing, is given a role in the designing of creatures rather less fundamental than that of the creator in natural theology. But it is just a metaphor, for all that, and Fodor is absolutely right to call it by its name. Fodor is right, I add, in just the same way that Hume was right to inveigh against the argument from design as resting upon an incomplete analogy.
Since, as Fodor might say, we can be morally certain that Hume never read Darwin, it might seem that what is at stake here is not so much the viability of Darwinism, but rather only of a certain philosophical position that has often been associated with Darwinism but that can exist without the fundamental insights of the theory of evolution and that indeed precedes that theory. Darwinism would then only be in serious trouble if it necessarily relies upon this philosophical position in order to explain the particular features of the world its defenders hope to make it explain. Kitcher and Coyne believe that "selecting-for" is largely a philosopher's invention, and would probably maintain that even if Darwin allowed nature to remain a bit too motherly in failing to cash the metaphor with which he begins the Origin, this in no way compromises the basic insight at the heart of the book, namely, that traits emerge gradually as individual members of a population that prove to be more fit for survival in given environmental circumstances manage to reproduce in greater numbers. They apparently do not expect Darwin the humble naturalist to offer a satisfying metaphysics of evolution, but only to tell us how evolution works. Fodor disagrees, on the grounds that unless a certain metaphysics is defended --that is, the one on which nature continues to have at least some minimal motherly capacity to guide the emergence of traits-- then we cannot coherently speak of one trait's being selected rather than another coextensive one. Therefore, Fodor thinks, natural selection does not support relevant counterfactuals, and is bad science.
I will not come down on one side or the other, but instead will wrap things up by a brief consideration of what I take to be the alternative path Fodor would like to see the philosophy of mind, and perhaps all disciplines concerned with humanity and its place in nature, go down. Fodor mentions evolutionary developmental biology, or evo-devo, as a promising new path of scientific research, seemingly taking it to be a radical break with the Darwinian orthodoxy of the past 150 years, rather than taking it, as leading scholars in the field such as Sean Caroll do, as a supplementation of the adaptationist program. For Fodor, evo-devo appears to point to a way of accounting for adaptive phenomena largely by appeal to endogenous constraints on phenotypes, though he also admits that this is at best a plausible guess.
In the end, Fodor doesn't really believe that he or anyone else needs to come up with a convincing alternative to adaptationism in order for him to keep on doing what he does best, since in his ideal version of the science of explaining both behavioral and physiological traits, the function of a trait could come to be understood in the absence of any understanding of its evolutionary history.
But can this really be done? Fodor rightly notes that evolutionary explanation is always diachronic: it tells you what an organ's function is now by giving an account of what it "was selected for way back then." He goes on to ask:
"Imagine, just as a thought experiment, that Darwin was comprehensively wrong about the origin of species (we all make mistakes). Would it then follow that the function of the heart is not to pump the blood? Indeed, that the heart, like the appendix, has no function, and that neither does anything else in the natural order? If you're inclined to doubt that follows, then the notion of function you have in mind probably isn't diachronic; a fortiori, it probably isn't Darwinian."
Fodor considers the example of William Harvey's discovery of the circulation of the blood, announcing that "Harvey didn't have to look outside physiology to explain what the heart is for." But is that really the case? Did Harvey understand the function of the heart? He discovered the circulation of the blood, but he also thought that the blood was returning to the heart because in some deep sense comprehensible only within the framework of Aristotelian natural philosophy, it longed to return home. In other words, Harvey looked way outside of physiology in order to explain what the heart is for.
While we're at it, we may as well also ask whether a modern-day creationist can understand the function of the heart. It depends what you mean by 'understand'. Fodor and a pentecostal preacher in Alabama would both agree that the heart is for pumping the blood, but would surely disagree as to why the blood is being pumped at all. My hunch is that Harvey's complete account probably has more in common with that of the preacher than it does with Fodor's own. Yet it seems that Fodor is not interested in complete accounts, or at least not in accounts complete enough for the differences between his, Harvey's, and the modern-day creationist's respective opinions as to why the blood is circulating to come into focus.
Fodor disagrees with Dennett's assertion that "Darwin didn't show us that we don't have to ask ['why questions']. He showed us how to answer them." The disagreement seems to stem from a deep conviction on his part that in order to understand a thing one need not consider that thing's history, that an adequate explanation of a thing's nature does not require an inquiry into that thing's origins. It is a deep, deep question whether this is true or not. It seems that as a programmatic point, the rejection of historical considerations might be perfectly acceptable for the purposes of psychology and the philosophy of mind. But Fodor wants to move from the partis pris he had earlier taken up in his groundbreaking work in these areas in order to denounce diachronic accounts not just of human minds but of biological entities in general. Indeed, as a result of his aversion to just-so stories, Fodor seems positively hostile to the scientific effort to --as Elliott Sober describes the task of evolutionary theory-- reconstruct the past.
But if diachronic considerations are excluded outright from the scientific answer to the 'why' questions concerning the nature of animals and humans among them, non-scientists will be more than happy to offer their own diachronic considerations, in the form of biblical citation and crypto-creationist ID-theory, in their own very different answers to the very same 'why' questions. It is the minimalist answer to the 'why' questions --it is, in other words, the naturalistic account of functions-- that the adaptationist program makes possible, and that is all too easy to give up once it is assumed --and not just as a thought experiment-- that Darwin was comprehensively wrong about the origin of species. This is not to say that natural selection should be retained as the myth the naturalists offer up in answer to that of the supernaturalists. It should be retained as the most plausible hypothesis, towards which the consilience of all sorts of inductions invariably points, even if Fodor's concern --like that of Gould and Lewontin-- about runaway adaptationism is a legitimate one, and even if we must acknowledge with Fodor that there are some scientific, and naturalistic philosophical, endeavors, in which evolutionary considerations have no place.
Berlin, April 22, 2008
For an extensive archive of Justin Smith's writing, please visit www.jehsmith.com.
Posted by Justin E. H. Smith at 02:49 AM | Permalink