"Tibetans can thrive at altitudes that would wreck most humans. Normally, exposure to altitudes exceeding 15,000 feet causes the blood to thicken, which can lead to cardiovascular problems and even death. But Tibetans have undergone extensive physiological and genetic changes, particularly in the regulatory systems of respiration and circulation. Specifically, they have an unusual variant of a gene involved in regulating the body's production of hemoglobin, the molecule that carries oxygen in the blood. This variant allows Tibetans to survive the low levels of oxygen."

"Remarkably, they acquired this capacity in as little as 3,000 years — and it would now appear that interbreeding with another human species [the Denisovans] may have had something to do with it."

Article on +io9: http://ow.ly/yKX5C 

Tibetans Got Their High-Altitude Gene From An Extinct Human Species
In what’s considered one of the finest examples of natural selection in action, Tibetans have acquired the ability to thrive at extremely high altitudes. Incredibly, researchers say the gene required for this adaptation was inherited from the now-extinct Denisovans.


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