DNA and Race: Tibetans Inherited High-altitude Gene from Ancient Race

The validity of race as an inherited genetic reality has been proven once again with the news that scientists have discovered a “superathlete” gene that helps Sherpas and other Tibetans breathe easy at high altitudes.

The discovery of this gene, reported by Nature magazine, was accompanied by the revelation that this gene was inherited from a now-extinct Homo erectus species who inhabited Siberia and the Far East.

The gene variant was identified as belonging to DNA extracted from remains found of the Denisova hominins, a Paleolithic-era species of the Homo erectus, first discovered in March 2010 at the remote Denisova Cave in the Altai Mountains in Siberia.

Analysis of the mitochondrial DNA (mtDNA) contained in the Denisova hominins remains showed it to be genetically distinct from the mtDNAs of Neanderthals and modern humans. Further study of its nuclear genome showed that it shared a common origin with the also now extinct Neanderthals. Around 3 to 5 percent of the DNA of Melanesians and Aboriginal Australians is derived from Denisovans.

Tibetans have long been famous for their ability to live and work at altitudes above 4000 meters (13,000 feet), where the limited supply of oxygen makes most other races ill.

Researchers discovered that Tibetans have several genes that help them use smaller amounts of oxygen efficiently, allowing them to deliver enough of it to their limbs while exercising at high altitudes.

Most notable is a version of a gene called EPAS1, which regulates the body’s production of hemoglobin. They were surprised, however, by how rapidly the variant of EPAS1 spread—initially, they thought it spread in 3000 years through 40 percent of high-altitude Tibetans, which is the fastest genetic sweep ever observed in humans—and they wondered where it came from.

Now, an international team of researchers has sequenced the EPAS1 gene in 40 Tibetans and 40 Han Chinese. Both were once part of the same population that split into two groups sometime between 2750 to 5500 years ago.

Population geneticist Rasmus Nielsen of the University of California, Berkeley, and his colleagues analyzed the DNA and found that the Tibetans and only two of the 40 Han Chinese had a distinctive segment of the EPAS1 gene in which five letters of the genetic code were identical.

When they searched the most diverse catalog of genomes from people around the world in the 1000 Genomes Project, they could not find a single other living person who had the same code.

Then, the team compared the gene variant with DNA sequences from archaic humans, including Neanderthals and Denisovans. The Denisovan and Tibetan segments matched closely.

The team also compared the full EPAS1 gene between populations around the world and confirmed that the Tibetans inherited the entire gene from Denisovans in the past 40,000 years or so.

Using computer modeling, Nielsen and his team found the only plausible explanation of how the gene was passed on was that the ancestors of Tibetans and Han Chinese got the gene by mating with Denisovans.

Some Han Chinese and mainland Asians retain a low level of Denisovan ancestry (about 0.2 to 2 percent), suggesting that much of their Denisovan ancestry has been wiped out or lost over time as their small populations were absorbed by much larger groups of modern humans.

Although most Han Chinese and other groups lost the Denisovans’ version of the EPAS1 gene because it wasn’t particularly beneficial, Tibetans who settled on the high-altitude Tibetan plateau retained it because it helped them adapt to life there. Thus the gene was favored by natural selection and spread rapidly to many Tibetans.

The discovery is the second case in which modern humans have acquired a trait from archaic humans, notes paleogeneticist Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, whose team discovered the Denisovan people. Earlier this year, another team showed that Mayans, in particular, have inherited a gene variant from Neanderthals that increases the risk for diabetes.

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