January 10, 2008
Spare a thought for the polar bear. Not only is it slandered as “one of nature’s most vicious beasts” by global-warming “sceptic” Brendan O’Neill ((Who, on the matter of global warming, cites the business-friendly political scientist Björn Lomborg, always a revealing sign.)), it is also now at the centre of a long-running philosophical/scientific debate occurring in the august pages of the London Review of Books.
Jerry Fodor, of whose writing on the philosophy of mind I have long been an admirer, there published an article on evolution last October called Why Pigs Don’t Have Wings. After reading it a couple of times I found myself scratching my head, wondering what exactly he was getting at. I felt slightly better after a variety of biologists and philosophers and other responders to the LRB letters pages in subsequent issues also signalled their uncertainty as to what exactly he was getting at. But we can be sure that it involved polar bears.
As he explains in the original article, Fodor thinks there is a conceptual problem with the theory of natural selection. The problem, in a nutshell, is as follows:
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.
“But,” you may respond (as I did, mentally), “for polar bears in the wild, ‘being white’ and ‘matching their environment’ are not two traits that we may label trait A and trait B while allowing that they are ‘coextensive’; they are the same trait.” ((As Tim Lewens’s letter subsequently pointed out: “[P]olar bears are camouflaged in virtue of being white.”)) A polar bear could not match its environment without being white; a polar bear could not be white and fail to match its environment. For a polar bear, being white just is matching its environment. Well, that is what I thought, and still do. Just because you can describe it in two ways doesn’t make it two different things. So there is no challenge for “adaptationism” here. Demanding that it be able to distinguish between one and the same thing seems a little unfair.
Let us leave the polar bears there for a moment, as they swim (I hope not too far) to the next ice floe. Fodor further argues that there is a problem with the implications of the vocabulary, often used in evolutionary theory, of an animal’s traits having been “selected for”. He writes:
It couldn’t, for example, be literally true that the traits selected for are the ones Mother Nature has in mind when she does the selecting; nor can it be literally true that they are the traits one’s selfish genes have in mind when they undertake to reproduce themselves. There is, after all, no Mother Nature, and genes don’t have, or lack, personality defects. Metaphors are fine things; science probably couldn’t be done without them. But they are supposed to be the sort of things that can, in a pinch, be cashed. Lacking a serious and literal construal of ‘selection for’, adaptationism founders on this methodological truism.
Now, up until the last sentence, this is all perfectly true, and a good illustration of how the idea of “natural selection” might in careless hands be seen as Unspeak, smuggling in an idea of purposiveness or even design. But of course, such language has long been understood as being merely a convenient shorthand for the mechanism that the theory actually proposes. Darwin himself made sure to point this out very clearly, at the end of Chapter 4 of On the Origin of Species:
But if variations useful to any organic being do occur, assuredly individuals thus characterised will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will tend to produce offspring similarly characterised. This principle of preservation, I have called, for the sake of brevity, Natural Selection.
There you go: for the sake of brevity — and, despite Fodor’s somewhat wilful display of bafflement, there is not much mystery as to what it is short for. This is explained patiently in a letter in the latest LRB from Simon Blackburn, Jerry Coyne, Philip Kitcher, Tim Lewens and Steven Rose:
In large numbers of articles and books, published from 1859 to the present, evolutionary biologists use the following style of explanation. A characteristic of an organism (the colour of an animal’s coat, say) is as it is because of a historical process. In 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.
So far, so good. But look, the polar bears are coming back!:
Is this incoherent? Nothing Fodor says bears on that question. Instead, he opposes a very particular way of presenting the explanation. Some people think we can talk of ‘selection for’ a characteristic, and identify rather precisely the traits that have been ‘selected for’. Fodor tries to argue that this is wrong: that there is no single correct answer (whether we know it or not) to the question of whether it was the whiteness of polar bears or their blending in with their surroundings that was ‘selected for’. Whether he is right is a philosophical issue about which people can disagree, but it has nothing to do with the coherence of Darwinian explanation. Natural selection proceeds if three elements are in place: variation in a trait, an effect of the variation on reproductive success, and some means by which the trait is inherited. Both the whiteness and the environmental blending emerged from the historical process that the selection explanation describes.
I admit that I don’t understand why Blackburn et al concede to Fodor his distinction between polar bears’ being white and their blending in with their surroundings, since, for the reasons given, I don’t believe these are separate things. In any case, the already soupy plot thickens and changes hue, as Fodor replies to their letter thusly:
Since the hypotheses that the bears were selected for being white and that they were selected for matching their environments support different counterfactuals (what would have happened if their environment had been orange?) they can perfectly well be distinguished in (for example, experimental) environments in which one trait is instantiated and the other one isn’t. I don’t claim that locally coextensive properties are indistinguishable in principle. I claim that, since the theory of natural selection fails to distinguish them, there must be something wrong with the theory.
I am not an evolutionary biologist, but I suppose that no one would seriously propose that predators in an orange environment would be selected for having white fur. Fodor only arrives at this artificially absurd possibility because he has split the single observed quality of polar bears being white-and-camouflaged into two properties, one with a potential to be universally applied (white), and one relative to a particular environment (camouflaged), supposing that the different verbalizations now point to two different things in the world. Let us hypothesize that polar bears in an orange environment would, ceteris paribus, at length become orange. Now, in an orange environment, being orange and being camouflaged are not two “locally coextensive properties”, they are the same property; just as in a white environment, being white and being camouflaged are the same property. What Fodor sneakily calls “the hypotheses that the bears were selected for being white and that they were selected for matching their environments” are not hypotheses plural, but a single hypothesis that takes into account, as it properly should, the features of the actual icy environment in which we observe polar bears splashing, gambolling, and viciously eating seals.
So I still don’t understand Fodor’s reason for there being “something wrong with the theory”. Any ideas?