High-altitude adaptation in humans

High-altitude adaptation in humans is an instance of evolutionary modification in certain human populations, including those of Tibet in Asia, the Andes of the Americas, and Ethiopia in Africa, who have acquired the ability to survive at altitudes above 2,500 meters (8,200 ft).^[1] This adaptation means irreversible, long-term physiological responses to high-altitude environments associated with heritable behavioral and genetic changes. While the rest of the human population would suffer serious health consequences at high altitudes, the indigenous inhabitants of these regions thrive in the highest parts of the world. These humans have undergone extensive physiological and genetic changes, particularly in the regulatory systems of oxygen respiration and blood circulation when compared to the general lowland population.^[2][3]

Around 81.6 million humans (approximately 1.1% of the world's human population) live permanently at altitudes above 2,500 meters (8,200 ft),^[4] which would seem to put these populations at risk for chronic mountain sickness (CMS).^[1] However, the high-altitude populations in South America, East Africa, and South Asia have lived there for millennia without apparent complications.^[5] This special adaptation is now recognized as an example of natural selection in action.^[6] The adaptation of the Tibetans is the fastest known example of human evolution, as it is estimated to have occurred between 1,000 BCE^[7][8][9] to 7,000 BCE.^[10][11]