A recent DNA study reported in Nature (512, 14 August 2014) indicates that Tibetans derive their ability to thrive at altitudes over 4000m without falling sick thanks to a gene inherited from the Denisovans, a hominin species which ranged across Asia before becoming extinct some 40,000 years ago.
Tibetans have adapted to the lower oxygen content at these altitudes because of a lower haemoglobin content in their blood. Amongst several genes which help them make efficient use of the lower oxygen levels, the most notable is one termed EPAS1. The team sequenced the region around the EPAS1 gene in 40 Tibetans and 40 Han Chinese. All 40 of the Tibetans had a distinctive segment of the EPAS1 gene but only two of the Han Chinese.
When a worldwide search was made on genomes from individuals tested in the 1000 Genomes Project, not a single other living person had the same code. Surprisingly, however, a close match was achieved with DNA from a finger bone from the skeleton of a Denisovan girl excavated in the Denisova Cave in Siberia.
Using computer modelling, the team surmise that the ancestors of Tibetans and Han Chinese acquired the gene through mating with the Denisovans. Most Han Chinese have lost the Denisovan version of the EPAS1 gene because it wasn’t particularly beneficial. However the people who settled on the Tibetan plateau retained it because it helped them survive in this environment.
This is the first time that scientists have been able to demonstrate that interbreeding with another hominin species has helped humans adapt to adverse conditions.