Many people have been asking me about these new papers in Science that demonstrate selection for some specific alleles involved in human brain development—I let it slide since John Hawks has already covered them. I think the papers are convincing: there have been recent patterns of selection for brain associated alleles in the last 5 or 6 thousand years for ASPM, and within 30-40 thousand years for another gene, called microcephalin. This isn't surprising at all—we expect that there are ongoing changes in the gene pool of all species; it's not as if we're exempt. It's also not surprising that they found brain-related genes that exhibit this pattern, because that's what the study was specifically designed to find. I'm sure that if they'd focused on pancreatic genes, they'd find similar patterns of unequal distribution and evidence of selection.

The important news is that people are evolving. This is another example of evidence in support of that contention, unexceptional except perhaps to creationists.

Unfortunately, one other aspect of this observation has also been brought up at Universal Acid and Foreign Dispatches: because the brain is so central to who we are, and because the distribution shows a low frequency of the selected alleles in sub-Saharan Africa, we can expect to see it seized upon by racists as supporting their claims. It doesn't, of course, no more than does the richer genetic diversity in African populations support the 'superiority' of Africans. It's a difference in a few components of a complex assemblage—and the operative word is 'different', not 'better'. The study is not dividing the world into people who have the gene, and those who don't. All of the subjects had fully functioning copies of the gene, with only subtle variations in its structure, variations that have effects that have not been determined.

The principal investigator of the study, Bruce Lahn, is very clear on avoiding premature conclusions about using this to evaluate ethnic groups.

Lahn emphasized that it would not be correct to interpret the findings as indicating that one ethnic group is more "evolved" than another. Any differences among groups would be minor compared to the large differences in such traits as intelligence within those groups, he said. "We're talking about the average impact of such variants," he said. "We still have to treat each individual as an individual. Just because you have one gene that makes you more likely to be a little taller, doesn't mean you will be tall, given the complex effect of all your other genes and of environment." Lahn also said that a multitude of other genes likely exist that influence brain size and development, and further research could reveal far more complex effects of natural selection on such genes.

Evans PD, Gilbert SL, Mekel-Bobrov N, Vallender EJ, Anderson JR, Vaez-Azizi LM, Tishkoff SA, Hudson RR, and Lahn BT (2005) Microcephalin, a Gene Regulating Brain Size, Continues to Evolve Adaptively in Humans. Science 309(5741):1717-1720.

Mekel-Bobrov N, Gilbert SL, Evans PD, Vallender EJ, Anderson JR, Hudson RR, Tishkoff SA, and Lahn BT (2005) Ongoing Adaptive Evolution of ASPM, a Brain Size Determinant in Homo sapiens. Science 309(5741):1720-1722.