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| Edmund Hillary and Sherpa Tensing were the first men to conquer Everest |
Sherpas like Tenzing Norgay, who along with Edmund Hillary first conquered Everest, have inherited genes from a long-extinct human sub-species that help them cope with living high in the mountains.
A 160,000-year-old jawbone found in a cave has revealed the ancient human species Denisovans lived at altitudes of 11,000ft.
Scientists say the extinct race of Neanderthal-like humans lived on the oxygen-starved Tibet plateau more than 100,000 years ago.
They also discovered the Denisovans passed on genes that help some modern-day people survive at high altitudes.
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| The Denisovan jawbone was found in a cave in China |
The jawbone was unearthed in Baishiya Karst Cave in Xiahe, China, which stands at an altitude of 10,760ft (3,280m).
It is the oldest hominin fossil ever found in the vast Himalayan region.
Previously, physical evidence of Denisovans had only been known from fossils from a single cave site in Siberia.
Traces of Denisovan DNA have been detected in present day Asian, Australian and Melanesian populations, suggesting that they may have once been widespread.
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| Scientists dated the jawbone to at least 160,000 years old |
Both Denisovans and their sister human sub-species, the Neanderthals, are known to have interbred with ancestors of people living today.
Most intriguingly, modern Sherpas - the ethnic group native to Nepal - and Tibetans appear to have inherited Denisovan genetic variants that help them cope with high altitudes.
The new find suggests Denisovans settled on the Tibetan plateau thousands of years before early modern humans, and the two groups later interbred.
Scientists were unable to find any DNA preserved in the fossil, but managed to extract proteins from one of the molar which proved it was Denisovan.
The well-preserved jawbone is robust with very large molars, features shared by Denisovans and Neanderthals, according to a study reported in Nature journal.
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| The jawbone fossil was discovered at Baishiya Karst Cave |
A heavy carbonate crust covering the fossil allowed scientists to date it to at least 160,000 years old.
The oldest specimens from "Denisova Cave" in Siberia are from a similar time period.
However, the Siberian site is only 700 metres (2,296ft) above sea level.
Modern day humans are not thought to have arrived on the Tibetan plateau until around 40,000 years ago.
Sherpas have lived in the Himalayas for at least 6,000 years and studies have shown that they have developed a physiology similar to that of a fuel-efficient car.
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| A virtual reconstruction of the Denisovan jawbone |
Their muscles get more mileage out of less oxygen than those of the average person.
Sherpas have mitochondria - tiny rod-like power plants in cells - that are extra-efficient at using oxygen.
While their red blood cell count is increased in thin mountain air, it remains below the point at which the blood thickens and strains the heart, causing altitude sickness.
The Denisovan jawbone was originally discovered in 1980 by a local monk.
He donated it to the sixth Gung-Thang Living Buddha, a Buddhist Lama, or teacher, who passed it to China's Lanzhou University.
