Wednesday, 17 October 2007

Jerry Fodor fails Evolution 101

The latest "fun" on the evolutionary (pro and anti) parts of the web has been discussion of an article in the London Review of Books by Jerry Fodor. In it he proclaims that natural selection is on its way out. Alas for him, his argument is based on an impressive ignorance of evolutionary biology. Jason Rosenhouse has done a good job taking down this mess, but still left something for the rest of us.

Fodor's claim is that there are two problems with theories of evolution by natural selection, one conceptual, one empirical. The conceptual problem first:
Here’s the problem: you can read adaptationism as saying that environments select creatures for their fitness; or you can read it as saying that environments select traits for their fitness. It looks like the theory must be read both ways if it’s to do the work that it’s intended to: on the one hand, forces of selection must act on individual creatures since it is individual creatures that live, struggle, reproduce and die. On the other hand, forces of selection must act on traits since it is phenotypes – bundles of heritable traits – whose evolution selection theory purports to explain. It isn’t obvious, however, that the theory of selection can sustain both readings at once.
Here he's bringing up a well-known issue, part of the levels of selection debate. The complete debate is more extensive than I'll describe here, and is largely solved. The problem that Fodor is focussing on is that genes code for traits - a gene might affect colour of a bear, for example, with one allele making it white. But, it is the whole bear that lives or dies. What, then, is being selected? Fodor:

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.
Of course, we do have an explanation, and one which does not rely on metaphor. Instead, we use mathematics. The ideas were developed by George Price, and the main result is the Price Equation. In the simpler form, it says that the change in the average value of a trait is equal to the covariance between the trait and fitness. Now, as fitness is measured on individuals, we have the explicit connection between a trait and selection. The more complex form of the Price equation allows for changes within individuals (e.g. if the environment changes, and this causes a change in the traits).

Price's equation helps us get Fodor out of the dilemma he's talked himself into:
Maybe one can, after all, make sense of mindless environmental variables selecting for phenotypic traits. ... 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.
Poor Fodor is going to asphyxiate as he waits for a theory that went shooting past him in the early seventies. Put simply, it doesn't matter whether we can distinguish between selection for traits A and B if they're correlated. Price tells us what will happen (and, of course, the Price is right). Some polar bears were whiter than white, and this meant that they were more likely to survive, and hence whiteness was correlated with fitness. Others presumably were a bluey-whiteness you'll really like, but this was correlated with a lower fitness. Hence that colour reduced in frequency. We can even deal with evolution of trait A when trait B is under selection - just follow the covariances!

Fodor's empirical problem is a wonderful straw man, dressed up in word salad. Follow this if you dare:
Adaptationism is a species of what one might call ‘environmentalism’ in biology. (It’s not, by any means, the only species; Skinnerian learning theory is another prime example.) The basic idea is that where you find phenotypic structure, you can generally find corresponding structure in the environment that caused it. Phylogeny tells us that phenotypes don’t occur at random; they form a more or less orderly taxonomic tree. Very well then, there must be nonrandomness in the environmental variables by which the taxonomic tree is shaped. Dennett has put this idea very nicely: ‘Functioning structure carries implicit information about the environment in which its function “works”. The wings of a seagull . . . imply that the creature whose wings they are is excellently adapted for flight in a medium having the specific density and viscosity of the atmosphere within a thousand metres or so of the surface of the Earth.’ So, phenotypes carry information about the environment in which they evolved in something like the way that the size, shape, whatever, of a crater carries information about the size, shape, whatever, of the meteor that made it. Phenotypes aren’t, in short, random collections of traits, and nonrandomness doesn’t occur at random; the more nonrandomness there is, the less likely it is to have been brought about by chance. That’s a tautology. So, if the nonrandomness of phenotypes isn’t a reflection of the orderliness of God’s mind, perhaps it is a reflection of the orderliness of the environments in which the phenotypes evolved. That’s the theory of natural selection in a nutshell.
Now, what he's trying to say (and I'll spare you the rest of the section) is that evolution is constrained - there are some things that a species can't evolve into, because they is no way of developing in that direction:

For example, nobody, not even the most ravening of adaptationists, would seek to explain the absence of winged pigs by claiming that, though there used to be some, the wings proved to be a liability so nature selected against them. 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.
I wonder in Prof. Fodor knows what chiroptera are? Of course, Fodor is right that there are developmental constraints. But so f*cking what? Of course that restricts how a species might evolve - it's one of the more powerful arguments for evolution by natural selection. It's why bats don't have feathers - they didn't evolve them, but found another way of taking to the air. This is why Fodor's problem is so silly - we know that there are endogenous constraints on species, but we also see that they still adapt. They work their way around problems the best they can, even if it means having a nerve 10 to 15 feet longer than it has to be. Fodor talks about species developing along one path, and that cutting out others, but why does this stop adaptation? I can't think of anyone who would have problems with this - hey, even game theorists understand it.

Apparently Fodor is writing a book with Massimo Piattelli-Palamarini about evolution without adaptation. Somehow I don't think it'll be about genetic drift.

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Monday, 15 October 2007

Lunacy and the Planets

I was just clearing my inbox, and found this in Science:

Excitation of Lunar Eccentricity by Planetary Resonances -- Cuk 318 (5848): 244 -- Science
I assume this means that lunacy and astrology are linked. Or perhaps that the star signs of werewolves are important.

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