Homo sapiens sapiens has spread across the globe and increased vastly in numbers over the past 50,000 years or so—from an estimated five million in 9000 B.C. to roughly 6.5 billion today. More people means more opportunity for mutations to creep into the basic human genome and new research confirms that in the past 10,000 years a host of changes to everything from digestion to bones has been taking place.
“We found very many human genes undergoing selection,” says anthropologist Gregory Cochran of the University of Utah, a member of the team that analyzed the 3.9 million genes showing the most variation. “Most are very recent, so much so that the rate of human evolution over the past few thousand years is far greater than it has been over the past few million years.”
“We believe that this can be explained by an increase in the strength of selection as people became agriculturalists—a major ecological change—and a vast increase in the number of favorable mutations as agriculture led to increased population size,” he adds.
“Ten thousand years ago, no one on planet Earth had blue eyes,” Hawks notes, because that gene—OCA2—had not yet developed. “We are different from people who lived only 400 generations ago in ways that are very obvious; that you can see with your eyes.”
Comparing the amount of genetic differentiation between humans and our closest relatives, chimpanzees, suggests that the pace of change has accelerated to 10 to 100 times the average long-term rate, the researchers write in Proceedings of the National Academy of Sciences USA.
Not all populations show the same evolutionary speed. For example, Africans show a slightly lower mutation rate. “Africans haven’t had to adapt to a fundamentally new climate,” because modern humanity evolved where they live, Cochran says. “Europeans and East Asians, living in environments very different from those of their African ancestors and early adopters of agriculture, were more maladapted, less fitted to their environments.”
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