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.
This explains some really interesting aspects of what has been called a great example of natural selection in human beings. The Tibetans gained this trait in less than 3000 years.The ability to survive at high altitude shows just how dramatically the environment has shaped human genomes.
And now we know that those genes came from non-human sources.
Kind of cool what DNA sequencing is now showing us about our human heritage. Just small amounts of ancient DNA from species we crossbred with still have an impact today.
The Tibetans are healthy at an air pressure that is 60% of what it is at sea level. I wonder just how low the air pressure could go for them to live? The Nepalese sherpas also have the relevant Denisovan genes and are able to survive altitudes on Mt. Everest that others require oxygen to survive. But people in the Andes have a different set of genes.
So I wonder what would happen if someone from Tibet has children with someone from the Andes? Would the children have the abilities to survive at even higher altitudes? And Ethiopians have a completely different set of genetic mutations from Andean or Tibetan sources..
The Armstrong limit is about 19,000 meters or about 12 miles, the point at which water boils at human body temperature. Even the most dense portion of the Martian atmosphere is 6 times less than this. So we would need to do extensive terraforming to raise the air pressure. But would these Tibetans be a likely group to make the first Martian settlers to live unencumbered by pressure suits?