Microcephaly genes associated with human brain size

Fresh from Science Daily are news on the genetic mechanism determining the size of the cerebral cortex:

Microcephaly genes associated with human brain size

ScienceDaily (Dec. 22, 2009) — A group of Norwegian and American researchers have shown that common variations in genes associated with microcephaly ... may explain differences in brain size ...

In relation to body size, brain size has expanded dramatically throughout primate and human evolution. In fact, in proportion to body size, the brain of modern humans is three times larger than that of non-human primates. The cerebral cortex in particular has undergone a dramatic increase in surface area during the course of primate evolution. ...

mutations in [The microcephaly] genes can reduce brain size by about two-thirds, to a size roughly comparable to our early hominid ancestors. There is also evidence that four of the genes -- MCPH1, ASPM, CDK5RAP2 and CENPJ -- have evolved rapidly and have been subject to strong selective pressure in recent human evolution....

The most statistically significant associations were consistently found with the areal expansion measure, which has implications also for future studies...

Highly significant associations were found between cortical surface area and polymorphisms in possible regulatory regions near the gene CDK5RAP2. ...

"One particularly interesting feature of this new discovery is that the strongest links with cortical area were found in regulatory regions, rather than coding regions of the genes," said Andreassen. "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 of the proteins of these genes. This has huge implications for future research on the link between genetics and brain morphology."