July 3, 2014
Tibetans Acquired Altitude Adaptation Genes From Ancient Human Relatives
redOrbit Staff & Wire Reports - Your Universe Online
A gene acquired from an extinct cousin of modern humans is responsible for helping Tibetans adapt to high altitudes, according to new research published online by the weekly science journal Nature on Wednesday.
Scientists from the University of California, Berkeley and Chinese genomics organization BGI-Shenzen found that Tibetans acquired the ability when their ancestors mated with Denisovans or individuals related to the now-extinct species. This is said to be the first time that a gene originating from a different species has been essentially proven to have helped modern humans adapt to the environment around them.
The variant in question is involved with the regulation of hemoglobin production in the body, affecting the molecule that is responsible for transporting oxygen in the blood. It became widespread several thousands of years ago, when Tibetans first relocated to the high-altitude plateau, and has allowed them to survive at elevations of more than 15,000 feet, despite the lack of oxygen and the tendency for people to develop cardiovascular problems.
“We have very clear evidence that this version of the gene came from Denisovans,” a human relative that went extinct about the same time as Neanderthals, approximately 40,000 to 50,000 years ago, principal author and UC Berkeley integrative biology professor Rasmus Nielsen explained in a statement. “This shows very clearly and directly that humans evolved and adapted to new environments by getting their genes from another species.”
In their study, Nielsen and his colleagues re-sequenced the area surrounding EPAS1, a hypoxia pathway gene previously liked to differences in hemoglobin concentration at high altitude, in 40 Tibetan and 40 Han individuals. They discovered that, in Tibetans, the gene possessed a highly differentiated haplotype previously observed only in the Denisovan genome, one Southern Han Chinese individual, and one Beijing Han Chinese individual.
According to the researchers, EPAS1 is activated when oxygen levels in the blood decrease, and triggers the production of more hemoglobin. It has also been called the “superathlete” gene, because some variants of it can help athletes quickly boost the oxygen-carrying capacity of their blood at low altitudes, thus increasing their endurance.
However, at high altitudes, the common variants boost hemoglobin too much, increasing the blood’s thickness and increasing the risk of high blood pressure, heart attack, low birth weight in babies, and higher infant mortality rates. The variant found in Tibetans, however, only increases hemoglobin levels slightly at higher elevations, meaning that they are immune to the side effects typically experienced by people at heights of over 13,000 feet.
“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,” said BGI-Shenzen scientist Xin Jin. “This unique finding may help us re-examine the similar fast-evolution cases in the future.”
“The genetic relationship or blood relationship between modern human and archaic hominins is a hot topic of the current paleoanthropology,” added fellow BGI researchers Asan Ciren. “The finding of Tibetans's selected EPAS1 haplotype in Denisovans not only demonstrates the possibility of ancient gene-flow from Denisovans… to ancestors of Tibetans, but also shows the importance of such events in local adaptation of modern humans.”