αEP: Complexity is not usually the product of selection

I mentioned in the last one this annoying tendency of too many pro-evolution people to cite “complexity” as a factor that supports the assertion of selection for a trait. Strangely, the intelligent design creationists also yell “Complexity!” at the drop of a hat, only it’s to prove that evolution can’t work.

They’re both wrong.

I ran across a prime example of this recently in a post by John Wilkins (It’s pick-on-John-Wilkins day! Hooray!)

Opponents, largely following Gould and Lewontin’s 1979 attack, tend to assert (often without consideration of the particular attempts to give adaptive explanations) that any and all adaptive hypotheses are cheap and to be avoided. This has the effect of basically eliminating natural selective accounts of anything. But we know that selection is the only process that results in complexity over any time, and the fact there are complex traits among organisms leads to the inevitable conclusion that we should be able to give selective explanations from time to time. I have argued before that we should think of adaptation as a viable hypothesis at all times; but being viable doesn’t make it true. The problem is not that EP or sociobiology makes adaptive hypotheses. They should. It is that they often make them without testing them.

I will concede the general point: a well-designed and testable adaptive hypothesis is a perfectly reasonable starting point to do science, and I agree that one big problem with evolutionary psychology is that most of their adaptive hypotheses are poorly done. But I’ve highlighted the chunk in the middle that’s just absurd: complex traits are the product of selection? Come on, John, you know better than that. Even the creationists get this one right when they argue that there may not be adaptive paths that take you step by step to complex innovations, especially not paths where fitness doesn’t increase incrementally at each step. Their problem is that they don’t understand any other mechanisms at all well (and they don’t understand selection that well, either), so they think it’s an evolution-stopper — but you should know better.

This is the trap Michael Behe falls into, too. It’s the assumption that you have to have an adaptive scenario for every step, and an inability to imagine non-adaptive solutions. I think if selection were always the rule, then we’d never have evolved beyond prokaryotes — all that fancy stuff eukaryotes added just gets in the way of the one true business of evolution, reproduction.

So let’s work through a hypothetical scenario of increasing complexity, and you try to see where selection is essential. And then I’ll give some real world examples.

Imagine an enzyme E with with a fairly nonspecific, broad spectrum of binding for various chemical substrates. It can bind substrate A or substrate B with equal facility, and then carries out some modification of the substrate — let’s say it hydrolizes some side group. We’ll call this enzyme E_AB for its substrates.

Now imagine a fairly common mutational event, a gene duplication. An individual in this population acquires a second copy of its gene, so now it is E_AB-E_AB. Is this event dependent on selection? No, obviously not.

But now this mutation spreads through the population, so a significant fraction of the individuals carry it. Is that dependent on selection?

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