New York, April 28 (IANS): Variants of five different genes -- including one originating in the extinct human subspecies Denisovans -- help Tibetans survive the harsh conditions of the high altitudes, says a study.

The people of Tibet have survived on an extremely high and arid plateau for thousands of years, due to their amazing natural ability to withstand low levels of oxygen, extreme cold, exposure to UV light and very limited food sources. 

For the study, published in the journal PLOS Genetics, the researchers sequenced the whole genomes of 27 Tibetans and searched for advantageous genes. 

"The comprehensive analysis of whole-genome sequence data from Tibetans provides valuable insights into the genetic factors underlying this population's unique history and adaptive physiology at high altitude," said study co-author Tatum Simonson from University of California San Diego in the US.

The analysis identified two genes already known to be involved in adaptation to high altitude, EPAS1 and EGLN1, as well as two genes related to low oxygen levels, PTGIS and KCTD12.

They also picked out a variant of VDR, which plays a role in vitamin D metabolism and may help compensate for vitamin D deficiency, which commonly affects Tibetan nomads. 

The Tibetan variant of the EPAS1 gene originally came from the archaic Denisovan people, but the researchers found no other genes related to high altitude with Denisovan roots.

Denisovans are believed to have gone extinct about 40,000 years ago.

Further analysis showed that Han Chinese and Tibetan subpopulations split as early as 44 to 58 thousand years ago, but that gene flow between the groups continued until approximately nine thousand years ago.