Split gene could have created human brains

SEATTLE, May 3 (UPI) -- A single gene mutation may have started the evolution of large human brains 2.5 million years ago as humans diverged from early cousins, U.S. researchers say.

Scientists at the University of Washington say the effect of a single gene that made two copies of itself was, paradoxically, to slow down individual brain development -- but this created time for neurons to develop more and better connections with one another, NewScientist.com reported Thursday.

Gene duplications do not happen often, geneticist Evan Eichler said, and only about 30 genes have copied themselves since humans split from chimpanzees 6 million years ago.

The duplication of the gene in question, SRGAP2, helped drive development of the neocortex, which controls higher-order brain functions such as language and conscious thought, researchers said.

SRGAP2 duplicated itself 3.5 million years ago, well after humans and chimps diverged, they said.

One million years later, this "daughter" of the original gene underwent its own duplication and created a "granddaughter" copy.

Those duplications, Eichler said, would have changed brain development immediately and dramatically, and human ancestors with two, three, or even more copies of SRGAP2 -- with consequently significantly differences in their cognitive abilities -- could have been inhabiting Earth together at some point.

"That's fun to think about," he said.