THE SECRET OF TIBETAN'S SUCCESS LIES WITH ANCESTORS WHO WERE NOT QUITE HUMAN
Researches have known for a while that many people alive today carry genes from human species other than Homo sapiens—the result of ancient interbreeding with Neanderthals and Denisovans. The plateau of Tibet is one of the most hostile places people inhabit. The air is thin and the weather cold. The locals, nevertheless, do well. And Rasmus Nielsen of the University of California, Berkeley, and his colleagues at BGI, a Chinese DNA-sequencing laboratory, suggest in this week’s Nature that one of the genes which lets them do so is Denisovan.
The gene Dr Nielsen has been investigating is a version of EPAS-1. This encodes part of a protein called hypoxia-inducible transcription factor 2-alpha. Transcription factors activate other genes, and this one (as its name suggests) does so in response to low oxygen levels. When that happens, it is responsible for stimulating the production of red blood cells, the growth of capillaries and the production of proteins involved in energy generation. Dr Nielsen and his team wanted to study the Tibetan version more closely, so they sequenced both it and the area around it in detail. When they did this they discovered that the block of DNA it inhabits is so similar to its Denisovan equivalent that it must originally have come from a mating (maybe more than one) between a Denisovan and Homo sapiens. Moreover, it is pretty much only Tibetans who have this version of the gene. Dr Nielsen established in 2010 that about 90% of them do, compared with fewer than 10% of their Han Chinese neighbours. He estimated that the altitude-friendly version became this widespread in Tibet in a mere 3,000 years.
The Economist, 5th July 2014