Gay

“What explains their advantage? Contrary to one popular theory, it’s not a high red-blood-cell count. Compared with Caucasians, Sherpas actually have fewer red blood cells per liter of blood. Nor is the difference explained by diet, acclimatization, metabolism, iron-deficiency, or environmental factors. At sea level, Sherpas have such a low red-blood-cell count that they are technically anemic, but, curiously, they don’t show symptoms. Overall, Sherpas require as much oxygen as anybody else, but they have less of it dissolved in their blood. Scientists initially found this puzzling. Red blood cells ferry oxygen around the body, and other populations well adapted to altitude, such as the Quechua and the Aymara of the Andean highlands, have veins teeming with red blood cells. How do Sherpas manage with less at a much higher altitude than the Andes? Probably by circulating blood faster. Sherpas have wider blood vessels. They breathe more often when at rest, providing their blood with more oxygen to absorb, and they exhale more nitric oxide, a marker of efficient lung circulation. There is also a genetic explanation. Sherpas’ red-blood-cell count stays low because of Hypoxia Inducible Factor 2-alpha, a gene that regulates response to low oxygen and turns on other genes. In addition, Sherpas have inherited a dominant genetic trait that improves hemoglobin saturation, allowing their red blood cells to soak up more oxygen. Sherpas’ thin blood, in turn, may prevent the sort of clotting that crippled Art Gilkey on K2. This genetic advantage only enhances the Sherpa mystique. Lowlanders clutching the Lonely Planet guide are convinced they want to hire “a sherpa,” even if they don’t know what a Sherpa is, and, after three generations of gathering tourist dollars, Sherpas now rank among the richest and most visible of Nepal’s fifty or so ethnicities. They didn’t start out that way.”
― Peter Zuckerman, Buried in the Sky: The Extraordinary Story of the Sherpa Climbers on K2's Deadliest Day