The human brain is still evolving. Microcephalin and ASPM (abnormal spindle-like microcephaly associated), two genes involved in brain development, have gone through positive selection in modern humans, according to research led by Bruce Lahn at the University of Chicago.12

Both genes went through strong positive selection in the hominid lineage leading to humans, Lahn says, "suggesting that the evolution of these two genes might have contributed to human brain enlargement." Now, analyses across roughly 90 ethnically diverse human samples show abnormally high frequencies favoring a specific haplotype for each gene. The high-frequency variant appears to have arisen 37,000 years ago for Microcephalin, and 5,800 years ago for ASPM – long after the estimated origin of modern humans about 200,000 years ago.

Aside from the association with microcephaly, however, the idea that the selection on these two genes was due to brain-size adaptation "is all speculation," said Morris Goodman...

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