Rapid evolution seen in Tibetans

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By Elizabeth Weise, USA TODAY
Tibetans may have undergone one of the fastest bouts of human evolution on record: Those having genes that allow them to thrive at high altitudes and low oxygen levels rose from 10% of the population to 90% in less than 3,000 years, a paper in the journal Science reports.

One genetic variant, the EPAS1 gene, allows Tibetans — many of whom live at 13,000 feet, where there is 40% less oxygen than at sea level — to thrive where others live with difficulty.

The research was conducted by scientists, from China, Denmark, and the Berkeley and Davis campuses of the University of California.

"This is the fastest genetic change ever observed in humans," says Rasmus Nielsen, UC Berkeley professor of integrative biology, who led the statistical analysis.

"If the selective pressure is strong enough, it certainly could happen in 150 generations," says Bruce Beutler, chairman of the genetics department at the Scripps Research Institute in La Jolla, Calif.

Most people coming to Tibet from sea level "immediately feel exhausted and can't perform well," says Nielsen. Eventually their bodies begin to produce more oxygen-carrying hemoglobin and they adapt to the environment. But Tibetans, because of their genetic variations, are able to function with lower levels of hemoglobin despite the lower oxygen.

The research also carries political overtones that are raising hackles in Tibetan circles. The researchers compared the genomes of 50 ethnic Tibetans and 40 Han Chinese and found evidence based on shared genetic traits that the Tibetan and Han populations diverged less than 3,000 years ago. They found more than 30 genes with DNA mutations that have become more prevalent in Tibetans than Han Chinese, nearly half of which are related to how the body uses oxygen.

The idea that Tibetans somehow descended from Han is problematic for Tibetan scholars. Archaeological evidence shows that people who were culturally Tibetan have been living on the Tibetan plateau for at least 11,000 years. Chinese scientists have for years "tried to use apparently scientific arguments to prove that Tibet is part of China or that Tibetans are part of the Chinese race, people, nation, or all three," says Robert Barnett, director of the Modern Tibetan Studies Program at the Weatherhead East Asian Institute at Columbia University.

The issue of whether Tibet should be an independent country is extremely politically sensitive in China. There were widespread riots in Tibet against Chinese control in 2008.

"What identifies a people isn't genetics, it's cultural heritage," Nielsen says. "I don't think this study has any implications for the debate about Tibetan independence and their right to self-determination."

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