While the roles of Microcephalin and ASPM in regulating brain size suggest that the selective pressure on the new variants may relate to cognition, Lahn emphasized that this possibility remains speculative. "What we can say is that our findings provide evidence that the human brain, the most important organ that distinguishes our species, is evolutionarily plastic," he said. Finding evidence of selection in two such genes is mutually reinforcing, he pointed out. "Finding this effect in one gene could be anecdotal, but finding it in two genes would make it a trend. Here we have two microcephaly genes that show evidence of selection in the evolutionary history of the human species and that also show evidence of ongoing selection in humans."
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.
Lahn speculated that the new findings suggest that the human brain will continue to evolve under the pressure of natural selection. "Our studies indicate that the trend that is the defining characteristic of human evolution ?
Source:Howard Hughes Medical Institute