The biological secrets that make Sherpas superhuman mountaineers

By Meera Senthilingam, for CNN

Updated 1139 GMT (1939 HKT) October 7, 2016

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Everest is the tallest mountain in the world, at 8,847 meters above sea level. Low oxygen at that altitude pushes human endurance to its limits. Pictured, Sherpa mountaineer Pemba Dorje Sherpa and others on Everest, 2009.