The Tibetan Plateau (map) rises more than 13,000 feet (4,000 meters) above sea level. At such heights, most people are susceptible to hypoxia, in which too little oxygen reaches body tissues, potentially leading to fatal lung or brain inflammation.

To survive the high life, many Tibetans carry unique versions of two genes associated with low blood hemoglobin levels, the researchers found.

Since hemoglobin is the oxygen-carrying component of red blood cells, the find might seem "really counterintuitive," said study leader Tatum Simonson at the University of Utah's Eccles Institute of Human Genetics in Salt Lake City.

"Usually, if you or I or any nonadapted