Peruvian Indian woman and Tibetan man (both from high altitude populations)。 (Her cheeks are red primarily due to increased
blood flow near the skin surface. More red
blood cells help her get oxygen to the tissues
of her body.)

The implication is that natural selection over thousands of years results in some populations being genetically more suited to the stresses at high altitude. However, different populations respond physiologically to low oxygen pressure in somewhat different ways. The primary solution of Indians from the high mountain valleys in Peru and Bolivia has been to produce more hemoglobin in their blood and to increase their lung expansion capability. Both result in an increase of oxygen carried by the blood. In contrast, the common solution of Tibetans and Nepalese who live at high altitudes generally has been to breathe faster in order to take in more oxygen and to have broader arteries and capillaries, thereby allowing much higher rates of blood flow and subsequently greater amounts of oxygen delivered to their muscles, despite the fact that they have relatively normal hemoglobin levels. A recent study of Tibetan villagers who live their lives at around 15,000 feet has shown that they have 10 oxygen-processing genes not commonly found in lowland populations. The EPAS1 gene is particularly important in adapting to environments with consistently low oxygen pressure.