The Denisovans, relatives of the Neanderthals who inhabited Asia before modern humans arrived, are known only from a scattering of small bones and a wealth of DNA data. So far, all of that originates from a single Siberian cave (called Denisova, naturally). Like the Neanderthals, the Denisovans interbred with those modern humans once they arrived. But the modern populations who have the most Denisovan DNA are far from Siberia, occupying southern Asia and some Pacific islands.
Now, a tiny fragment of Denisovan DNA has also been found in a group that’s much closer to Siberia: the Tibetans. And all indications are that it helps them adapt to the extreme elevations of the Tibetan plateau.
Large parts of that plateau are 4,000 meters (2.5 miles) above sea level. The populations native to the area have lower infant mortality and higher birth weights than people who have relocated to the area. In addition, the Tibetans have acclimated to the altitude without relying on increased red blood cell counts, which is how most other people respond after spending time at altitude. Higher red blood cell counts mean a more viscous blood, which creates its own health hazard, so this difference is also likely to be very advantageous.
We could use a little of that Denisovan DNA up here on the Front Range. My first day of life above 6,000 feet, I unloaded my few material goods from the Ryder van I’d rented in San Francisco, sat down on a pillow (I didn’t have a sofa yet) with a beer, and promptly passed out. Even just a small amount of physical labor can leave you exhausted, until your body has had enough time to adapt to the high elevation.
There are stages, too.
In my experience, life doesn’t seem much different between sea level and about 4,000 feet or so. Get north of there though, and elevation effects kick in. At 7,500 feet (which is about where I live now) further adaptation is needed. And then again at 9,000. At 10,000 things can get really tough — except, apparently, for those with that Denisovan DNA.