When did humans start exploiting high altitude environments? High altitudes are generally defined as areas that are at least 8,000 feet (2,400 meters) above sea level. These environments are extremely difficult for survival, mainly due to the fact that they are oxygen-depleted and resources are scarce. Oxygen is the most important element for life, and its deficiency is detrimental to life, resulting in a condition known as hypoxia, when oxygen level in body tissues is very low. However, modern humans have occupied high altitude regions for millennia. There is now evidence that early human ancestors may have reached the Tibetan Plateau as early as 160,000 years ago. The evidence for this comes from fossil evidence found in the Tibetan Plateau indicating the presence of the Denisovans in the area at that time. The Denisovans were a group of archaic humans who lived in most of Asia as early as 200,000 years ago. The earliest modern human occupation of high-altitude environments on a permanent basis is documented from two sites: The Bale Mountains in highland Ethiopia (47,000 to 36,000 years ago) and the Tibetan Plateau (40,000 to 30,000 years ago). Humans occupied the Andean highlands permanently at least 7,000 years ago. Read about Denisovan DNA.

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