But he just came to mine. Larry Moran is a biochemist at the University of Toronto, and he runs a great blog writing a fair bit about evolution. He is on the side of Gould and Lewontin in the neutralist/selectionist debate in evolution. In the comments to a post from this morning, Dawkins, Darwin, Drift, and Neutral Theory, I asked for examples of traits that are known to have evolved via drift, rather than natural selection. Not that there aren't any traits that are thought not to be adaptive, but to make the point that we know that they are neutral just as much or little as we know others are adaptive, and that many traits must be adaptive, and that I think Moran is overemphasizing the importance of drift in evolution. Here's Moran's response:
It's shocking to me that you would have to ask such a question in 2011. As a graduate student interested in evolution you should be very familiar with the common examples and the debate.I honestly didn't appreciate that much if at all, and neither did Richard Dawkins:
Lewontin likes rhinoceros, I like tongue rolling. Some people can roll their tongues and some can't? Is this an adaptive trait?
I admit that these particular examples aren't going to change the course of evolution but it's all that's required to establish the real possibility that alleles with visible phenotypes can be neutral.
Once we've agreed on that point we can discuss whether the evolution of blood types in different human populations is due to selection or drift. (The answer is drift.)
Your other examples are more complicated but many of them arise from a combination of all the important mechanisms of evolution, not just natural selection.
I anticipate that you are going to fall back on the old canard that none of these traits have been proven beyond all reasonable doubt to be the result of random genetic drift acting on nearly neutral alleles, therefore it's permissible to say they all must be adaptations. If you don't see the flaw in that logic then there's no point in continuing.
"Shocking"? Isn't that rather a patronising and arrogant response to Mr Østman?It's Dr. now, btw.
Lewontin's guess that the difference between two-horned and one-horned rhinoceroses is non-adaptive is just that: a pure guess. Here is what Lewontin wrote:
"For example, the Indian rhinoceros has one horn and the African rhinoceros has two. Horns are an adaptation for protection against predators, but it is not true that one horn is specifically adaptive under Indian conditions as opposed to two horns on the African plains." (cited, together with my reply, in The Extended Phenotype, the chapter called 'Constraints on Perfection':
Actually, it seems unlikely that horns are an adaptation against predators. Lewontin is being too adaptationist here. Horns are more likely an adaptation against other rhinos, both as weapons and as displays. In which case it could very well be the case that one horn is best for Indian rhinos and two horns best for African rhinos (because a rhino has to match whatever is the norm for its competitors in its own region).
Never mind Lewontin's ignorance about the biology of rhinoceroses. The point is that Moran has no more right to assume, with Lewontin, that the number of rhinoceros horns is neutral than anybody else has the right to assume that they are under selection. Even if I could not invoke sexual selection (which makes it positively likely that Lewontin is wrong) Moran would have no right to assume that this is a good example of a neutral trait, still less would he have the right to patronise Bjørn Østman in that way.
Tongue-rolling is a polymorphism (I can 't do it, you very possibly can) which makes it more complicated. In this case we are not seeking an adaptive advantage in tongue-rolling per se. We are seeking some kind of balance between the two sides of the polymorphism. I don't know enough about it (nor does Moran) but I would keep an open mind, and the first place I would look would be for some kind of balancing selection (or perhaps heterozygous advantage) with tongue-rolling as a pleiotropic byproduct. Once again, the last thing I would do is simply assume in my ignorance (and Moran's ignorance) that selection is not involved.
Do go read the full exchange.