Monday, October 15, 2007


Jerry Fodor critiques Natural Selection - why pigs don't have wings

Here's a chronological series of quotations from a fascinating article by atheist philosopher of mind Jerry Fodor, 'Why Pigs Don't Have Wings', in the London Review of Books, 18th October 2007 (with some comments from yours truly):

'Darwin’s theory of evolution has two parts. One is its familiar historical account of our phylogeny; the other is the theory of natural selection, which purports to characterise the mechanism not just of the formation of species, but of all evolutionary changes in the innate properties of organisms. According to selection theory... environmental selection for fitness is (perhaps plus or minus a bit) the process par excellence that prunes the evolutionary tree.'

'More often than not, both halves of the Darwinian synthesis are uttered in the same breath; but it’s important to see that the phylogeny could be true even if the adaptationism isn’t. In principle at least, it could turn out that there are indeed baboons in our family tree, but that natural selection isn’t how they got there.'

This is just what Michael Behe argues in The Edge of Evolution. Behe accepts the phylogeny but rejects 'adaptationism' as the mechanism explaining (most of) it.

'In fact, an appreciable number of perfectly reasonable biologists are coming to think that the theory of natural selection can no longer be taken for granted. This is, so far, mostly straws in the wind; but it’s not out of the question that a scientific revolution – no less than a major revision of evolutionary theory – is in the offing... The ironic upshot is that at a time when the theory of natural selection has become an article of pop culture, it is faced with what may be the most serious challenge it has had so far. Darwinists have been known to say that adaptationism is the best idea that anybody has ever had. It would be a good joke if the best idea that anybody has ever had turned out not to be true. A lot of the history of science consists of the world playing that sort of joke on our most cherished theories.'

'History might reasonably credit Stephen J. Gould and Richard Lewontin as the first to notice that something may be seriously wrong... Their 1979 paper, ‘The Spandrels of S. Marco and The Panglossian Paradigm: A Critique of the Adaptationist Programme’, ignited an argument about the foundations of selection theory that still shows no signs of quieting. A spandrel is one of those more-or-less triangular spaces that you find at the junctures of the arches that hold up a dome. They are often highly decorated; painters competed in devising designs to fit them. Indeed (and this is Gould and Lewontin’s main point), casual inspection might suggest that the spandrels are there because they provide the opportunity for decoration; that, an adaptationist might say, is what spandrels were selected for. But actually, according to Gould and Lewontin, that gets things backwards. In fact, spandrels are a by-product of an arch-and-dome architecture; decide on the latter and you get the former for better or worse. Arches were selected for holding up domes; spandrels just came along for the ride. I assume that Gould and Lewontin got their architectural history right, but it doesn’t really matter for the purposes at hand. What matters is that though spandrels survived and flourished, nothing at all follows about what, if anything, they were selected for. To a first approximation, you have spandrels if and only if you have a dome that’s supported by arches; the two are, as logicians say, coextensive. Is it, then, that selection for arches explains why there are spandrels? Or is it that selection for spandrels explains why there are arches? It looks, so far, as though the story could go either way; so what tips the balance? Surely it’s that domes and arches are designed objects. Somebody actually thought about, and decided on, the architecture of San Marco; and what he had in mind when he did so was that the arches should support the dome, not that they should form spandrels at their junctures. So that settles it: the spandrels weren’t selected for anything at all; they’re just part of the package. The question, however, is whether the same sort of reasoning can apply to the natural selection of the phenotypic traits of organisms, where there is, by assumption, no architect to do the deciding. If cathedrals weren’t designed but grew in the wild, would the right evolutionary story be that they have arches because they were selected for having spandrels? Or would it be that they have spandrels because they were selected for having arches? Or neither? Or both?'

A very interesting critique I haven't come accross before - the argument seems to be that evolution by natural selection lacks explanatory power, because it doesnt allow one to specify an answer to Fodor's question, not merely in practice but also in principle. Of course, a theory that could answer it, at least in principle, is ID!

'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. The answers that have been suggested so far have not been convincing.'

'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.'

A very nice admission of how naturalistic metaphysics enters into and constrains scientific theorising so that it is not free to follow the evidence. Lets just repeat that: 'Getting... God's mind in particular, out of biological explanations is a main goal of the [evolution by natural selection] programme'!

'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.'

'It wouldn’t be unreasonable for a biologist of the Darwinist persuasion to argue like this: ‘Bother conceptual issues and bother those who raise them. We can’t do without biology and biology can’t do without Darwinism. So Darwinism must be true.’ Darwinists do often argue this way; and the fear of hyperbole seems not to inhibit them. The biologist Theodosius Dobzhansky said that nothing in biology makes sense without Darwinism, and he is widely paraphrased. The philosopher Daniel Dennett says that ‘in a single stroke, the idea of evolution by natural selection unifies the realm of life, meaning and purpose with the realm of space and time, cause and effect, mechanism and physical law.’ (Phew!) Richard Dawkins says, ‘If superior creatures from space ever visit earth, the first question they will ask, in order to assess the level of our civilisation, is: “Have they discovered evolution yet?”’ Shake a stick at a Darwinist treatise and you’re sure to find, usually in the first chapter, claims for the indispensability of adaptationism. Well, if adaptationism really is the only game in town, if the rest of biology really does presuppose it, we had better cleave to it warts and all. What is indispensable therefore cannot be dispensed with, as Wittgenstein might have said. The breaking news, however, is that serious alternatives to adaptationism have begun to emerge; ones that preserve the essential claim that phenotypes evolve, but depart to one degree or other from Darwin’s theory that natural selection is the mechanism by which they do. There is now far more of this sort of thing around than I am able to survey.' (my emphaisis)

Of course, one of those alternatives, not mentioned by Fodor, is ID.

'Nobody expects to find fossils of a species of winged pig that has now gone extinct. Rather, pigs lack wings because there’s no place on pigs to put them. To add wings to a pig, you’d also have to tinker with lots of other things. In fact, you’d have to rebuild the pig whole hog: less weight, appropriate musculature, an appropriate metabolism, an apparatus for navigating in three dimensions, a streamlined silhouette and god only knows what else; not to mention feathers. The moral is that if you want them to have wings, you will have to redesign pigs radically. But natural selection, since it is incremental and cumulative, can’t do that sort of thing. Evolution by natural selection is inherently a conservative process, and once you’re well along the evolutionary route to being a pig, your further options are considerably constrained; you can’t, for example, go back and retrofit feathers. That all seems reasonable on the face of it; but notice that this sort of ‘channelling’ imposes kinds of constraint on what phenotypes can evolve that aren’t explained by natural selection. Winged pigs were never on the cards, so nature never had to select against them. How many such cases are there?'

But if, once you have an animal, it's evolutionary possibilities are tightly constrained, how much confidence can one have that it can undergo much evolution at all? One might get bigger and smaller pigs, with different skin coloring and larger or smaller tusks, or without tails, or whatnot. But if a pig cannot become a bird, what else can't it become, and what can it become besides another pig, or pig-like animal? In other words, don't the sort of constraints Fodor highlights count against any macro-evolutionary scenario, of whatever mechanism? Simply assuming that a gradual functional path from A to Z exists, because evolution won't work without it, would be question begging. The mechanism it would count least against is obviously intelligent design - but even there one might think it quite a task to turn a pig into a bird, etc., through a series of intermediate steps each of which is viable in its own right...

'the notion of natural selection is conceptually flawed'

'Lacking arches, domes fall down; so arches are selected for supporting domes. But arches are linked to spandrels for reasons of geometry; so spandrels aren’t selected for, they are ‘free riders’ on selection for arches. The moral is that phenotypic traits can carry information about linkages among the mechanisms that produce them. Free-riding is always suggestive of such linkages, and free-riding is ubiquitous in evolution.'

'the classical Darwinist account of evolution as primarily driven by natural selection is in trouble on both conceptual and empirical grounds. Darwin was too much an environmentalist. He seems to have been seduced by an analogy to selective breeding, with natural selection operating in place of the breeder. But this analogy is patently flawed; selective breeding is performed only by creatures with minds, and natural selection doesn’t have one of those.'

On evolutionary psychology: 'in point of logic, this sort of explanation has to stop somewhere. Not all of our traits can be explained instrumentally; there must be some that we have simply because that’s the sort of creature we are. And perhaps it’s unnecessary to remark that such explanations are inherently post hoc (Gould called them ‘just so stories’); or that, except for the prestige they borrow from the theory of natural selection, there isn’t much reason to believe that any of them is true.'

'The high tide of adaptationism floated a motley navy, but it may now be on the ebb. If it does turn out that natural selection isn’t what drives evolution, a lot of loose speculations will be stranded high, dry and looking a little foolish. Induction over the history of science suggests that the best theories we have today will prove more or less untrue at the latest by tomorrow afternoon. In science, as elsewhere, ‘hedge your bets’ is generally good advice.'

On evolutionary psychology again: '...I wouldn’t think of arguing that we are either mostly happy or mostly good. But I doubt that’s because of what our minds were selected for. Maybe the real trouble is that our neurones aren’t hooked together quite right, or that some of our hormones aren’t entirely reliable; with the effect, in either case, that getting some of the things we want isn’t compatible with getting the others. Or that some of them we can’t have at all. Anyhow, for what it’s worth, I really would be surprised to find out that I was meant to be a hunter-gatherer since I don’t feel the slightest nostalgia for that sort of life. I loathe the very idea of hunting, and I’m not all that keen on gathering either. Nor can I believe that living like a hunter-gatherer would make me happier or better. In fact, it sounds to me like absolute hell. No opera. And no plumbing.'

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