Fascinating stuff…read this paper in PNAS, Evidence that the adaptive allele of the brain size gene microcephalin introgressed into Homo sapiens from an archaic Homo lineage, or this short summary, or John Hawks’ excellent explanation of the concepts, it’s all good. It’s strong evidence for selection in human ancestry for a gene, and just to make it especially provocative, it’s all about a gene known to be involved in brain growth, and it’s also showing evidence for interbreeding between Homo sapiens and Neandertal man.
The short short explanation: a population genetics study of a gene called microcephalin shows that a) it arose and spread through human populations starting about 37,000 years ago, b) this particular form of the gene (well, a small cluster of genes in a particular neighborhood) arose approximately 1.1 million years ago in a lineage distinct from that of modern humans, and c) the likeliest explanation for this difference is that that distinct lineage interbred with modern humans 37,000 years ago, passing on this particular gene variant that was then specifically selected for, a process called introgression.
The work looks sound to me, and I’m convinced. The one thing to watch for, though, is that there will be attempts to overreach and couple possession of this gene to some kind of intellectual superiority. We don’t know what this particular variant of the gene does yet! All we can say at this point is that some abstract data shows that a particular allele spread through the human population at a rate greater than chance would predict, that the gene itself has as one of its functions the regulation of brain growth, but that it is highly unlikely that that particular function is affected by the variant. Whatever it does, I expect the role is more along the lines of subtle fine-tuning rather than simply making people smart.