Try to walk a mile in a Tibetan person's shoes and you will fail miserably. That's because they have evolved to live at high altitudes better than anyone else on the planet.
Just in time for the climbing season to open on Mount Everest, a new study from the University of Texas, Houston, tells us about the genes behind this incredible ability.
Why do the University of Texas researchers want to study the Tibetan population?
It's estimated that humans have been continually living on the Tibetan plateau for almost 60,000 years. That gives a lot of time for adaptations to develop and populations to evolve in order to live better in these extreme conditions.
When you are up there high on the Tibetan plateau, life is tough. When I was in Tibet in 2010 and again in 2011, it was amazing how hard it was just to walk around. There are a lot of high-altitude places in the world, but Lhasa, at an altitude of 3,600 metres, is one of the highest places where humans have lived for thousands of years.
I spoke with Chad Huff, the senior author of the study.
"Tibetan high-altitude adaptation is perhaps the most extreme example we have of human adaptation where most individuals from low altitude have a very difficult time at 15,000 feet," he said. "Tibetans survive and thrive there, so it's really fascinating as to the genetics behind those adaptations."
And that's what this new paper, published in the Open Access Journal PLOS, investigated; they looked at the genetic changes in Tibetans that make them such great mountaineers.
What did they find?
After sequencing the complete genomes of 27 Tibetans, they identified five possible genes that relate to the Tibetans' ability to thrive at such high altitudes. Two of them, EGL1 and EPAS1, have been previously found, and both seem to be related to how much hemoglobin is in the blood.
Hemoglobin is what carries oxygen in the blood. When you acclimate to higher altitudes, your body adjusts to the low oxygen concentrations by making more hemoglobin to suck up more of that hard-to-get oxygen.
The two genes, EGL1 and EPAS1, found in Tibetan populations seem to be doing the opposite: they seem to be decreasing the hemoglobin concentrations.
This makes no sense, until you realize that having blood thick with hemoglobin makes your heart pump harder and your vessels strain more. Having a heart that works harder all the time, coupled with vessels that are strained, doesn't add up to a healthy individual. This is one problem observed with the ethnic Han population, the dominant population of lowland China who are trying to live in the Tibetan plateau to take advantage of some of the resource extraction that is happening. The non-Tibetans show significant negative health effects, while the Tibetans show no such problems.
How fast is 'fast evolution'?
There's no exact number yet, but it looks like some of these genetic changes are as recent as 10,000 years old. The most common adaptation, and the one with the most variability in the population, is 45,000 years old. But still, that's pretty quick in evolutionary time, especially in humans who reproduce relatively slowly.
Chad Huff offers more insight.
"It is quite fast for humans. There are a few examples of somewhat faster evolution in humans, the lactase persistence in Europeans is one example; it's a few thousand years younger, but EPAS1 and EGL1 are among the strongest signals and fastest sweeps in human evolution."
You have to remember, the selective pressures — the forces that pick the strongest individuals to survive — are strong up there on the plateau. I can speak from experience. When I was hiking to Everest base camp it was one step breathe, two steps, breathe. I couldn't believe how hard it was, and there was my Tibetan guide, sprinting by, seemingly unfazed.
Do these results help explain why Sherpas manage several trips up Everest a season?
Yes, the study showed that Tibetans are literally genetically superior to anyone else trying to summit.
When I was there my guide had been to camp 4, the last one before the summit, more than a handful of times. That would be considered a huge success for most people attempting to climb Everest, and yet it was largely uncelebrated.
There is no doubt that in mountaineering, the earlier lack of credit for the Sherpas has been a huge controversy. Maybe because it is so much easier for them, it's almost as if the rest of the world hasn't been acknowledging the incredible risks they take because it's so natural.
And yet, more Sherpas have been killed on Everest in the last three climbing seasons than ever before. And now we embark on another Everest climbing season, poised to the busiest ever.
The Sherpas are the lifeline to the mountain; no one can climb it without them. They set the routes, fix the ropes, carry a lot of the gear and do it better than anyone else on the planet.
Summitting Everest is an absolutely monumental achievement, and what the Tibetan people have survived and how they've adapted to the life in the mountains is equally monumental.