Microcephaly Genes Associated With Human Brain Size.

In the third chapter of NOT A CHIMP I explain that Bruce Lahn's "quick and dirty" route to human brain evolution, based on the recent selection of variants for two genes associated with microcephaly, foundered because a number of research groups around the world, including his own, could find no links between variants of these genes and measurements of brain size in modern populations. However, this group has found a new and much more accurate way of measuring cortical surface area and they report significant associations between C.S.A. and variants of the CDK5RAP2 gene involving changes to its regulatory region. They conclude: "One particularly interesting feature of this new discovery is that the stronger links with cortical area were found in regulatory regions, rather than in the coding regions of the genes. One upshot of this may be that in order to further understand the molecular and evolutionary processes that have determined human brain size, we need to focus on regulatory processes rather than further functional characterization (changes in amino-acid sequence) of the proteins of these genes. This has huge implications for future research on the links between genetics and brain morphology."

This group did not, it appears, attempt to discover the age of the evolution of the regulatory variants they examined but it will be very interesting if they choose to investigate ASPM and Microcephalin, the two genes Lahn worked on and which tipped him into hot political water!