AsianScientist (Jul 4, 2014) – Tibetans may have to thank an extinct race of humans, the Denisovans, for their ability to survive at high altitudes.
In response to the low oxygen content of air (hypoxia) at high altitudes, the body increases production of red blood cells. However, this leads to the thickening of blood, which causes uneven blood flow through the lungs and could lead to high blood pressure or stroke. Scientists have struggled to understand why Tibetans, who live at elevations of 4,000 meters above sea level all their lives, seldom experience these negative effects.
One potential explanation is a mutation in the gene EPAS1, which is found in 87 percent of Tibetans but only nine percent of Han Chinese, even though the two groups diverged only 3,000 years ago. EPAS1 is involved in the hypoxia pathway and was shown to be associated with differences in hemoglobin concentration at high altitude.
In this study published in Nature, researchers re-sequenced the region around EPAS1 in 40 Tibetan and 40 Han individuals and found that EPAS1 in Tibetans had a highly differentiated haplotype. What was surprising was that this haplotype was only observed in the Denisovan genome but not in other populations worldwide, except for a single Southern Han Chinese and a single Beijing Han Chinese individual.
Denisovans are an ancient hominid that went extinct about the same time as the Neanderthals. They were known to have interbred with modern humans coming out of Africa as they migrated into Southeast Asia, explaining the presence of Denisovan DNA in Melanesians. The finding that Tibetan EPAS1 is nearly identical to Denisovan EPAS1 suggests that Tibetans also interbred with Denisovan hominids.
“The Denisovan-like DNA we found in the genome of Tibetans implied that the adaptation to local environments could be facilitated by gene-flow from other hominins who have been adapted to such environments. This unique finding may help us re-examine the similar fast-evolution cases in the future,” said Dr. Jin Xin, a research scientist from BGI who conducted the study.
“The genetic relationship between modern humans and archaic hominins is a hot topic of in current paleoanthropology. The finding of Tibetans’s selected EPAS1 haplotype in Denisovans not only demonstrates the possibility of ancient gene-flow from Denisovans or Denisovan-like populations to the ancestors of Tibetans, but also shows the importance of such events in local adaptation of modern humans,” said Dr. Asan Ciren also from BGI.
The article can be found at: Huerta-Sánchez et al. (2014) Altitude adaptation in Tibetans caused by introgression of Denisovan-like DNA.
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