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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.
"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 is it's almost impossible for evolution not to happen." Still, the findings also 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.
The finding hints that farmers in what is now Turkey drove the language boom - and not later Siberian horsemen, as some linguists reckon.
Russell Gray and Quentin Atkinson, of the University of Auckland in New Zealand use the rate at which words change to gauge the age of the tree's roots - just as biologists estimate a species' age from the rate of gene mutations.
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," noted lead researcher Bruce Lahn, a University of Chicago geneticist whose studies appear in Friday's edition of the journal Science.Lahn offers an analogy: Medieval monks would copy manuscripts and each copy would inevitably contain errors — accidental mutations.Years later, a ruler declares one of those copies the definitive manuscript, and a rush is on to make many copies of that version — so whatever changes from the original are in this presumed important copy become widely disseminated.
The differences between words, or DNA sequences, are a measure of how closely languages, or species, are related.