Look out, future, because here we come: scientists say the speed of human evolution increased rapidly during the last 40,000 years ó and itís only going to get faster.
The findings, published today by a team of U.S. anthropologists in the Proceedings of the National Academy of Sciences, overturn the theory that modern lifeís relative ease has slowed or even stopped human adaptation. Selective pressures are still at work; they just happen to be different than those faced by our distant ancestors.
"Weíre more different from people 5,000 years ago than they were from Neanderthals," said study co-author and University of Utah anthropologist Henry Harpending.
In the study, researchers analzyed genomes from 270 people belonging to four disparate ethnic groups: Han Chinese, Africaís Yoruba tribe,
Japanese and Utah Mormons. By comparing areas of difference and similarity, they determined that about seven percent of the genome has undergone significant change since the end of the last Ice Age.
If human beings had always evolved at such a rapid clip, said the researchers, genetic differences between people and chimpanzees would be 160 times greater than they are.
Driving the changes are environmental fluctuations and population growth. As the number of people swells, so do the number of mutations generated by random chance. Further selecting for disparate genetic inheritances are the diverse terrains, climates and social structures inhabited since the glaciers retreated.
The findings contradict the hypothesis that evolution must be slowing down because people who once would have died are sustained by modern medicine and social safety nets. They also suggest that genetic differences between different ethnic groups can be significant.
"The actual genes that are sweeping have not been thoroughly identified in all cases, but we can see interesting patterns," said Harpending.
"There are something like 6 genes, all broken African genes, responsible for European light skin, blue eyes, blonde hair, etc. They are evolving fast in Europe. Meanwhile, other genes responsible for light skin are sweeping in Asia, and they are different from those in
Asked about James Watsonís controversial claims that intelligence evolved less effectively in people of African descent, Harpending said the study wasnít designed to test such characteristics. He also cautioned against interpreting the findings as suggesting that people are becoming fundamentally better.
"Some of the mutations let us do better. We can eat simple carbohydrates, which hunter-gatherers never did. But we may also be accumulating damaging stuff," said Harpending.
He wondered whether social changes might not cultivate unfortunate tendencies.
"Evolution is a double-edged sword," he said. "What evolution cares about is that I have more offspring. If you can do it by charming and manipulating, and Iím a hardworking farmer thatís going to feed the kids ten years down the road, then youíre going to win. Hit-and-run, irresponsible males are reproducing more. That isnít good for anyone except those males, but thatís evolution."
The studyís ultimate message, said Harpending: "Whatever changes are happening, theyíre happening faster."
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