Sherpas have been biologically wired over thousands of years to give them exceptional mountaineering skills, research shows.
A new study indicates that the Nepalese ethnic group, originating from the Himalayas, have evolved over time so they are better equipped to deal with thin mountain air.
Tests revealed striking differences between the Sherpa and other humans in relation to mitochondria, energy production and the immune system.
As part of their research scientists compared a group of 15 Sherpas and "lowland" researchers during an expedition to Mount Everest.
And their findings shed light on why the Asian population is better able to cope in rigorous mountainous conditions - notably low levels of oxygen.
Among their findings, scientists found that Sherpa mitochondria, tiny "batteries" in cells that supply energy, were more efficient than those of most people.
They were also more likely to obtain energy from sugars instead of by burning fat - an option normally chosen only at times of extreme physical stress.
Another key finding involved levels of phosphocreatine, an "emergency" energy source that helps muscles contract when the body's usual energy molecule, ATP, is lacking.
After two months at high altitude, phosphocreatine levels in the lowlanders crashed, but in the Sherpas they increased.
The Sherpas also seemed to possess a natural protection against harmful free radicals.
The destructive molecules, which damage cells and tissue, can be generated by lack of oxygen. Their levels normally soar at high altitudes, but in Sherpas they remained very low.
Researcher Dr Andrew Murray said: "Sherpas have spent thousands of years living at high altitudes, so it should be unsurprising that they have adapted to become more efficient at using oxygen and generating energy.
"When those of us from lower-lying countries spend time at high altitude, our bodies adapt to some extent to become more 'Sherpa-like', but we are no match for their efficiency."
Sherpas are well-known for supporting thousands of Himalayan expeditions.
Two Sherpas are known to have reached the summit of Mount Everest, the world's tallest mountain, 21 times.