Friday, 12 February 2010

Why Jerry Fodor Doesn't Have Laser Eyes

It's now over 150 years since Darwin and Wallace presented the case for natural selection, and by now you'd think it's a non-issue. But no, it's just one of those ideas that keeps sustaining criticism. Usually from creationists who are seeking to push their moral doctrine by pushing for the necessity of God, but in this case it's not to put God in there.

Jerry Fodor and Massimo Piattelli-Palmarini have fired a broadside at natural selection. First with an article two years ago, and now a book (and accompanying New Scientist article). After 150 years and plenty of experimental support, Fodor has come along and tried to argue the whole concept to be incoherent. Not an attack on evolution, just on the underlying mechanism touted to explain it.

Throwing the baby out with the bathwater
The problem with reconstructing our past under current evolutionary framework is the danger of making post-hoc rationalisations that might not have any bearing on reality. That while there may be the potential to create a story for survival value that may not be the case. What we are describing might simply be a by-product of something else that was selected for, or just happened to be a product of chance.

The realisation is that not everything about us can be directly selected against. The question of why is blood red shouldn't be put down to anything that has to do with being selected for the colour. But there's little doubt that the reason the colour of blood is red to begin with is because of selection - selection on the ability to carry oxygenated blood cells.

And this is where I feel Fodor is throwing the baby out with the bathwater. From the extreme of using selection to explain everything to explaining nothing at all. Are polar bears selected for being white or selected for being camouflaged? It really doesn't matter because the fact that they're white means that they're camouflaged in their present environment.

Fodor has taken the metaphor of natural selection and turned it into a tautology. Skin may not be designed for getting dirty, but the fact that it can get dirty doesn't mean that there haven't been survival advantages to the way our skin is now. You don't throw the baby out with the bathwater just because the baby gets dirty in the first place!

Why don't pigs have wings? It's a simple enough question with a simple enough answer. Yet Fodor labours out this point as if there's something profoundly paradoxical about a world with wingless pigs in it. Flight has evolved multiple times in tetrapods, and there are many more animals who can't fly but can glide. But pigs aren't one of them, nor do they ever look likely to make it in the air.

The simple answer is contingency, the evolutionary algorithm can only ever modify what's already there. So wings develop not as extra appendages but as modifications of existing appendages. Birds didn't have wings spring up, but modified their arms. Same for bats, same for pterosaurs. Why would we expect winged pigs to begin with when nothing about their lifestyle should lead to such winged creatures?

The surprising thing is that Fodor seems to think this somehow contradicts natural selection, yet contingency has been part of modern evolutionary theory for decades now. Of course it's doing to be that way, descent with heritable modification, how can we expect it to be anything else? The constraints itself build what is possible through the process, the selection is what of those possibilities carry on.

Contingency and developmental constraints play a role, no doubt. But it's not the whole story, and doing away with natural selection is just as problematic as trying to explain every facet of life with it.

The necessity of natural selection
As a species we are essentially blind. All the colours of the rainbow is just a tiny fraction of the electromagnetic spectrum. So why is it we can see only these frequencies of light? Natural selection does give an answer - it happens to correspond with the black body radiation of the sun as seen through our atmosphere. The European kestrel has a modification on its violet opsin gene that allows it to see in the ultra-violet. Why? It just so happens that its prey, the vole, signals with urine that reflects in the ultra-violet.

Meanwhile there have been nocturnal creatures sequenced, whose violet opsin genes have been shot to pieces. In dim-light, such abilities aren't really needed and thus not selected for or against. Just as moles or cave-fish are blind - it just doesn't matter to their survivability if they have sight or not. Makes perfect sense under natural selection.

Natural selection works because the algorithm works. It's able to filter through variation that arises because of the survival advantages and disadvantages that development brings. The process of accumulated advantageous or neutral variation, and the deletion of disadvantageous mutation as per the environmental constraints is what makes the idea so powerful. Evidentially it's not the answer to life, the universe and everything, but remove it completely from biology and nothing makes sense.

Let it be borne in mind how infinitely complex and close-fitting are the mutual relations of all organic beings to each other and to their physical conditions of life. Can it, then, 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 the rejection of injurious variations, I call Natural Selection. Variations neither useful nor injurious would not be affected by natural selection, and would be left a fluctuating element, as perhaps we see in the species called polymorphic." - Charles Darwin (The Origin Of Species, Chapter 4)

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