Washington: In a ground breaking discovery, researchers have found that Tibetans were able to adapt to high altitudes thanks to a gene picked up when their ancestors mated with a species of humans they helped push to extinction.
This is the first time a gene from another human species has been shown unequivocally to have helped modern humans adapt to their environment.
An unusual variant of a gene involved in regulating the body`s production of haemoglobin - the molecule that carries oxygen in the blood - became widespread in Tibetans after they moved onto the high-altitude plateau several thousand years ago.
This variant allowed them to survive despite low-oxygen levels at elevations of 15,000 feet or more whereas most people develop thick blood at high altitudes, leading to cardiovascular problems, researchers from University of California (UC), Berkeley, claimed.
"We have very clear evidence that this version of the gene came from Denisovans, a mysterious human relative that went extinct 40,000-50,000 years ago, around the same time as the more well-known Neanderthals, under pressure from modern humans," explained Rasmus Nielsen, professor of integrative biology at UC Berkeley.
"This shows very clearly and directly that humans evolved and adapted to new environments by getting their genes from another species," he noted.
The gene, called EPAS1, is activated when oxygen levels in the blood drop, triggering production of more haemoglobin.
At high altitude, the common variants of the gene boost haemoglobin and its carrier, red blood cells, too much, increasing the thickness of the blood and leading to hypertension and heart attacks.
The variant or allele found in Tibetans raises haemoglobin and red blood cell levels only slightly at high elevation, avoiding the side-effects seen in most people who relocate to elevations above 13,000 feet.
"We found part of the EPAS1 gene in Tibetans is almost identical to the gene in Denisovans and very different from all other humans," Nielsen emphasised.
For the study published in the journal Nature, Nielsen and his colleagues subsequently sequenced the EPAS1 gene in an additional 40 Tibetans and 40 Han Chinese.
The data revealed that the high-altitude variant of EPAS1 is so unusual that it could only have come from Denisovans, the study concluded.