Interesting study that postulates that Tibetan Sherpas perhaps got their genes from Denisovans.
As modern humans migrated out of Africa, they had to adapt to many new environments. One noteworthy adaptation was of Tibetans adjusting to the thin air of the Tibetan plateau, which at about 2.5 miles (4 kilometers) in altitude has oxygen levels just 60 percent that of air at sea level. For instance, when at high altitudes, women who come from low altitudes usually have problems with childbirth, such as preeclampsia, which is potentially dangerous high blood pressure during pregnancy
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As modern humans migrated out of Africa, they had to adapt to many new environments. One noteworthy adaptation was of Tibetans adjusting to the thin air of the Tibetan plateau, which at about 2.5 miles (4 kilometers) in altitude has oxygen levels just 60 percent that of air at sea level. For instance, when at high altitudes, women who come from low altitudes usually have problems with childbirth, such as preeclampsia, which is potentially dangerous high blood pressure during pregnancy
More here
