The evolution of a large, complex brain has been the defining feature of the human lineage – although human brain size has not changed over the past 200,000 years. But it is not apparent whether the new genetic adaptations discovered in human brains have any effect on brain size, or intelligence.
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"Whatever advantage these genes give, some groups have it and some don't. This has to be the worst nightmare for people who believe strongly there are no differences in brain function between groups," says anthropologist John Hawks of the University of Wisconsin in Madison, US.
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The new mutation is also much more common among people from Europe, the Middle East, and the Americas than those from sub-Saharan Africa.
