WASHINGTON -- The human brain may still be evolving.
So suggests new research that tracked changes in two genes thought to help regulate brain growth, changes that appeared well after the rise of modern humans 200,000 years ago.
That the defining feature of humans, our large brains, continued to evolve as recently as 5,800 years ago, and may be doing so today, promises to surprise the average person, if not biologists.
''We, including scientists, have considered ourselves as sort of the pinnacle of evolution," said lead researcher Bruce Lahn, a University of Chicago geneticist whose studies appear in today's edition of the journal Science.
''There's a sense we as humans have kind of peaked," agreed Greg Wray, director of Duke University's Center for Evolutionary Genomics. ''A different way to look at it is it's almost impossible for evolution not to happen."
Still, the findings are controversial, because it's far from clear what effect the genetic changes had or if they arose when Lahn's ''molecular clock" suggests -- at roughly the same time period as some cultural achievements, including written language and the development of cities.
Lahn and colleagues examined two genes that are connected to brain size. If those genes don't work, babies are born with severely small brains, called microcephaly.
Using DNA samples from ethnically diverse populations, they identified a collection of variations in each gene that occurred with unusually high frequency. In fact, the variations were so common they couldn't be accidental mutations, but instead were probably due to natural selection, where genetic changes that are favorable to a species quickly gain a foothold and begin to spread, the researchers report.