Westerners who visit the Himalayan Mountains in Nepal usually find themselves making use of the services of Sherpa people who are native to the region. Sherpa bearers and guides not only know the best routes through the mountains, and are able to carry loads that are way beyond what most westerners could manage, but they are also able to breathe the rarified air at high altitudes that has their guests reaching for oxygen supplies.

A Sherpa guideCredit: McKay Savage. Licensed under the Creative Commons Attribution 2.0 Generic licence.

Scientists now believe that they have found the answer to why the Sherpas have these abilities. It is all down to a gene that Sherpas carry and which is absent in just about everyone else. The gene derives from an ancient human species, the Denisovans, who died out more than 40,000 years ago. It appears that the ancestors of today’s Sherpas lived alongside the Denisovans and interbred with them, which is how they acquired the gene in question. The knowledge that the Denisovans had this gene comes from DNA analysis of material taken from a cave in Russia.

The special gene, which is a variant of a gene that non-Sherpa people have, has the effect of restricting the production of red blood cells when oxygen levels drop. The normal response to low oxygen availability is for the body to produce more haemoglobin (in red blood cells) to transport the oxygen that is still available, the “plan” being to ensure that as few oxygen molecules as possible go to waste. However, this has the effect of thickening the blood to a dangerous level in that the arteries become blocked, the heart has a much more difficult task in pumping the thick blood, and a heart attack can easily be the result. 

The gene variant found in both Denisovan and Sherpa DNA only allows haemoglobin production to be raised to a limited extent when oxygen levels are low. At 13,000 feet above sea level oxygen can be 40 per cent less available, and most Himalayan peaks are a lot higher than that. For most humans, venturing to such heights without additional oxygen is very risky, but the Sherpas have far fewer problems in that regard.

The suggestion is therefore that the Denisovans evolved a gene variant that allowed them to live at high altitudes, and, although they have been extinct for a very long time, this ability has continued because the gene was passed on to the Sherpas.

Foreigners who pay large sums of money for the privilege of climbing Mount Everest and other Himalayan peaks therefore have not only the Sherpas of Nepal to thank for doing all the heavy work, but also a species of humans who have not existed for at least 40,000 years.