They’ve finally done it. Bruce Lahn’s lab has an article in PNAS (review here) showing evidence for introgression of a gene from an archaic Homo species into the modern human genome. They suggest the possibility that Neanderthals are that archaic species. That’s right: there are Neanderthals among us (at least in small portions of our genome).
For those of you interested in the details, here’s a brief summary. The gene in question, microcephalin (MCPH1) has an interesting pattern of polymorphism. The approximate coalescence time for all MCPH1 alleles in humans is approximately one million years ago — much longer ago than other human genes. That’s because there is one haplotype that diverged from all the other alleles a million years ago and evolved independently from the other haplotypes. It then introgressed with the other alleles about 37,000 years ago, back when there were multiple Homo species walking the earth. Lahn and colleagues argue that the two groups of alleles evolved separately because they were found in different species or lineages. At least one mating event introduced the MCPH1 gene into the modern human lineage from the other lineage.
On top of the Neanderthal-modern love story is the fact that this gene plays an important role in brain development. And there is evidence that it has been subject to recent positive selection in the human genome. Some people are going to interpret this to mean that modern humans got smart by borrowing a gene from Neanderthals. While this is very good evidence for interbreeding between the modern human lineage and an archaic species, I’d be reluctant to reach any conclusions regarding the evolution of human mental capacity from these data.
Evans PD, Mekel-Bobrov N, Vallender EJ, Hudson RR, and Lahn BT. 2006. Evidence that the adaptive allele of the brain size gene microcephalin introgressed into Homo sapiens from an archaic Homo lineage. PNAS In press. doi: 10.1073/pnas.0606966103