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New research suggests that the defining feature of humans large brains continue to evolve as recently as 5,800 years ago, and may be doing so today.

The scientists make their claim based on the recent evolutionary history of two genes -- microcephalin and abnormal spindle-like microcephaly-associated (ASPM) -- which appear to regulate brain size.

Over thousands of years, both genes seem to be generating new and improved versions of themselves -- beneficial mutations that are spreading rapidly among the human population to reshape and strengthen brain capacity.

In the Sept. 9 issue of Science, Bruce Lahn of the University of Chicago and his colleague report on the results of two genetic analyses -- the first conducted among 90 men and women and a chimpanzee, and the second among almost 1,200 men and women.

The researchers initially focused on identifying all the variations -- or mutations -- of microcephalin and ASPM genes present among the participants. They then honed in on one particular class of each of the two genes that appeared more abundant and genetically younger than the rest.

For the microcephalin gene, the variation arose about 37,000 years ago, about the time period when art, music and tool-making were emerging, Lahn said. For ASPM, the variation arose about 5,800 years ago, roughly correlating with the development of written language, spread of agriculture and development of cities, he said.

Lahn and his team observed that each of the gene classes were present among a significant number of the scanned subjects -- 30 percent in the case of the ASPM mutation, and 70 percent in the case of the microcephalin mutation.

The ASPM mutation was more prevalent in European-related populations such as Iberians, Basques, Russians, North Africans, Middle-Easterners, and South Asians, and less often found among sub-Saharan Africans, East Asians, and Native American Indians.

The microcephalin variant was also found with higher frequency outside of sub-Saharan Africa.

Their findings suggest that each of the two brain gene mutations thrived and spread due to an active "selection" process, with the mutations conferring an evolutionary advantage to each carrier. Enditem

(Agencies)

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