These populations have successfully lived & reproduced at high altitude for hundreds of generations with hypoxia as a constant evolutionary pressure. Consequently, they are likely to have undergone natural selection toward a genotype (& phenotype) tending to offer beneficial adaptation to sustained hypoxia. \ Although many places on the planet have resident populations above 3,OOO m, the elevation at which the majority of people demonstrate physiological changes to hypobaric hypoxia, three main regions host populations over 4,OOO m. These are the Tibetan plateau & Himalayan valleys, the South American Andes, & the Ethiopian Highlands (158). \ Evidence related to Tibetan oxygen saturations is inconsistent. Numerous studies have demonstrated arterial oxygen saturations (SaO2) at rest & during submaximal &\or maximal exercise to be greater in Tibetans & Sherpas compared with lowlanders (29, 33, 48, 56, 82, 146, 164, 176, 177). This is evident from birth (117). \ KING OF THE MOUNTAINS: TIBETAN & SHERPA PHYSIOLOGICAL ADAPTATIONS FOR LIFE AT HIGH ALTITUDE.