Tibetans took less than 3,000 years to adapt to living at high altitude, said a new study. "This is the fastest genetic change ever observed in humans," said Rasmus Nielsen, a University of California Berkeley biology professor who led the statistical analysis and genome-wide comparison between the Tibetans and the Han Chinese.
     According to the study, the Tibetans and the Han Chinese split into two separate populations some 2,750 years ago, with the larger group moving to the Tibetan plateau where it dwindled while the low-elevation Han expanded dramatically. The Tibetans, however, quickly evolved a unique ability to live above 4,000 meters (13,000 feet), where oxygen levels are 40 percent lower than those at sea level. "For such a very strong change, a lot of people would have had to die simply due to the fact that they had the wrong version of a gene," said Nielsen.
     Comparing the genes of both ethnic groups, researchers 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. One mutation in particular spread from fewer than 10 percent of the Han Chinese to nearly 90 percent of all Tibetans. It is near a gene called EPAS1 that codes for a protein involved in sensing oxygen levels and perhaps balancing aerobic and anaerobic metabolism.
    When people from lower elevations move above 4,000 meters they typically tire easily, develop headaches, produce babies with lower birth weights and have a higher infant mortality rate. Tibetans have none of these problems, despite lower oxygen saturation in the blood and lower levels of hemoglobin levels, which gives blood its red color, and binds and transports oxygen to the body's tissues.  "The new finding is really the first time evolutionary information alone has helped us pinpoint an important function of a gene in humans," Nielsen said.
   
Sources: AFP, Yahoo! News (1 July 2010)