As thousands of serious climbers (and Jim Whittaker) know too well, Mt. Everest's summit has about a third as much oxygen as there is at sea level. The thin air alone can leave even the most able-bodied climber reeling – with dizziness, headaches, and, in serious cases, swelling of the brain. And yet Sherpas, a small population of Tibetans hailing from the eastern Himalayas, are able to withstand the hypoxic conditions without developing the chronic sicknesses that afflict lowlanders. While it was once speculated that Sherpas developed their knack for mountaineering through acclimatization, researchers from Chinese and Tibetan universities now have the strongest evidence yet that the answer lies in Sherpa DNA .
Hong-Xiang Zheng, who studies anthropology and evolutionary biology at Fudan University in Shanghai and co-authored the study, selected 76 unrelated Sherpas and focused on mitochondria because of their role in regulating energy production in the body. "Mitochondria help determine the degree of respiratory fitness by controlling the metabolic rate and use of oxygen," says Zheng. Mitochondrial DNA also has a high mutation rate, making it a likely source of any related adaptations.
The research revealed that distinct mitochondrial lineages became increasingly common when the Sherpas left Tibet for the higher elevations of Nepal several hundred years ago. This leads Zheng to believe that these mitochondrial changes are the key to their tolerance of the low-oxygen conditions in the Himalayas.
Along with populations in the Andes and Ethiopian Highlands, Sherpas are genetically suited to life at altitude, and, for now, there aren't any shortcuts for the rest of us. With more research, scientists could find a way to manipulate mitochondria to give the rest of us the same tolerance to altitude. But that breakthrough is likely years away. Until then, lowlanders who want to climb Everest will just have to slowly acclimatize themselves to higher altitudes – and probably hire a Sherpa to carry their oxygen.