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Changing Regions of Genome Suggest Evolution is Still Occurring in Humans

By Nicholas Wade
THE NEW YORK TIMES

Providing the strongest evidence yet that human beings are still evolving, researchers have detected some 700 regions of the human genome where genes appear to have been reshaped by natural selection, a principal force of evolution, within the last 5,000 to 15,000 years.

The genes that show this evolutionary change include some responsible for the senses of taste and smell, digestion, bone structure, skin color and brain function.

Many of these instances of selection may reflect the pressures that came to bear as people abandoned hunting and gathering for settlements and agriculture, a transition well under way in Europe and East Asia some 5,000 years ago.

Under natural selection, beneficial genes become more common in a population as their owners have more progeny.

Three populations were studied, Africans, East Asians and Europeans. In each, a mostly different set of genes had been favored by natural selection. The selected genes, which affect skin color, hair texture and bone structure, may underlie the present-day differences in racial appearance.

The study of selected genes may help physical anthropologists explain why people over the world have a such a variety of distinctive appearances, even though their genes are on the whole very similar, said Spencer Wells, director of the Genographic project of the National Geographic Society.

The finding adds substantially to the evidence that human evolution did not grind to a halt in the distant past, as is tacitly assumed by many social scientists. Even evolutionary psychologists, who interpret human behavior in terms of what the brain evolved to do, hold that the work of natural selection in shaping the human mind was completed in the pre-agricultural past, more than 10,000 years ago.

“There is ample evidence that selection has been a major driving point in our evolution during the last 10,000 years, and there is no reason to suppose that it has stopped,” said Jonathan Pritchard, a population geneticist at the University of Chicago who headed the study. He and his colleagues, Benjamin Voight, Sridhar Kudaravalli and Xiaoquan Wen, report their findings in Tuesday’s issue of PLoS-Biology, a peer-reviewed, open-access journal published by the Public Library of Science, a nonprofit organization.

The researchers’ data is based on DNA changes in three populations gathered by the HapMap project, a venture that built on the decoding of the human genome in 2003. The data, though collected to help identify variant genes that contribute to disease, also provide evidence of evolutionary change.

The fingerprints of natural selection in DNA are hard to recognize. Just a handful of recently selected genes have previously been identified, like those that confer resistance to malaria or the ability to digest lactose in adulthood, an adaptation common in northern Europeans whose ancestors thrived on cattle milk.