A Gift for Thin Air

When modern humans met Denisovans, the encounter left a gift that still helps people today. Tibetans inherited a Denisovan version of a gene called EPAS1.

Up high, the air holds less oxygen, so lowlanders' bodies flood the blood with extra red cells to compensate — a response that, taken too far, brings on altitude sickness. The Denisovan EPAS1 variant blunts that overshoot. It lets Tibetans live and work at extreme elevation — on a plateau averaging above 3,500 meters — without the thickened blood that sickens visitors. Evolution was a braided stream, not a straight line, and these ancient gifts still flow through us.