Climate and Human Culture
In addition, examples can be found of human differences in tolerance to climatic conditions through prolonged acclimatization. Among them are the ability of persons native to Tierra del Fuego to sleep in freezing temperatures, and of persons native to the high Andean mountains to live with half the oxygen values found at sea level. Prolonged genetic selection appears to have developed functional differences, such as the greater number of sweat glands in peoples native to tropical regions, and the higher blood flow and surface temperature in those native to Arctic regions. Many common diseases also show a relationship to climatic variations, but a direct cause-and-effect correlation is difficult to establish. For one, it is hard to differentiate weather-induced illnesses from other illnesses; for two, great changes have taken place in sanitation and health education through time.