Real-Life X-Men: Biology of the world's greatest climbers -- the Sherpa

Forget Xavier's School for the Gifted -- Marvel instead at the real-life superheroes on the roof of the world.



For years amongst climbers, anecdotes circulated about Sherpas' apparent superhuman ability to function at high altitude, when all others succumbed to mountain sickness -- or worse. Now science has shown how they have evolved to live in one of the most inhospitable environments on Earth.

Thousands of years living in the thin air of the Himalayan plateau has given Sherpa peoples a biology that differs from lowlanders at the very cellular level.

Watch the video or read the transcript below:

Francis: People from different parts of the world have different genetic characteristics. That's fairly obvious. An easy one to spot is, of course, skin color. But as the name suggests, this is only skin deep and a poor way to determine genetic difference. For example, there's more genetic diversity on the continent of Africa than the entire rest of the world. Since this video is about superpowers, I'm not sure that skin color really confers any unless, of course, you count being more resistant to sunburn or less likely to be stopped by the police. Yet, we do have real-life X-men living amongst us. Not literally amongst us unless you live on the roof of the world. The Sherpa are an ethnic group originally from Tibet and now residing in Nepal, and they are the greatest climbers in the world. No, not that kind of climbing. I mean that they can climb higher and perform better at high altitude than any other humans on the planet.

[MUSIC]

Male: Everybody says, "I climbed Everest." Wrong. It is Sherpas who climb. It is Sherpas who take us to Everest.

Male 1: Sherpas are honestly the greatest human beings on the planet.

Francis: To understand some of the concepts, we're going to need a crash course in altitude medicine. At sea level, atmospheric pressure is one atmosphere. At 5,500 meters, it's half an atmosphere. At the summit of Mount Everest, it's less than a third. The proportion of air around you that's made up of oxygen is the same, 21%, but there's just less of it. There's less of everything. The air is thinner. The body struggles to survive in an environment it was never evolved to experience, unless of course, you are a Sherpa. Now don't get this confused with acclimatization. That's the essential process that mountaineers have to go through before they ascend the high summits.

Remember, we talked about hematocrit in a previous video. That's the amount of red cells, and hence, hemoglobin in your blood. Now cyclists may boost this with drugs, but you can do it naturally just by existing at altitude as your body attempts to deal with the low oxygen levels by increasing the oxygen-carrying capability of your blood. You also start to hyperventilate, breathe faster. This blows off carbon dioxide. Carbon dioxide is acidic, so your blood starts becoming alkalotic or more alkaline. Your kidneys then have to try to compensate and correct your pH. This sounds okay so far, right? Well, we need to talk about hypoxic pulmonary vasoconstriction or HPV. Hypoxia, from the Greek hypo, meaning low and axia, meaning oxygen. Let's say you've got a damaged part of your lung. Low oxygen is detected and blood vessels contract to try to divert blood to healthy bits of lung instead. There's no point supplying dead lung with blood, but at altitude, your lungs detect low oxygen everywhere, even if your lungs are completely healthy. The blood vessels contract all over, reducing gas exchange, making the whole situation worse.

In a process we don't really fully understand, changes in blood vessels cause fluid to leak out into your lungs and around your brain. These two complications are called high-altitude pulmonary edema and high-altitude cerebral edema, and they require urgent descent because they can kill. Sadly, any boost in your hemoglobin is temporary. After I came down from altitude, I returned to being a sea-level sucker in a matter of weeks. Even if I had stayed at altitude my entire life, my son would have still been born with the physiology of a lowlander, even though as you can see, he is a natural-born mountaineer. Yet, even if a Sherpa is born and raised in Holland, their kids will still be born with adaptations making them better suited to altitude than their Dutch school friends even if the highest they've ever climbed is the top of a windmill, so this is genetic. Let's get to the good bit.


What actually are these mutant superpowers that I'm raving about? Tales of Sherpa resilience abound. They've been found on the mountainside, semi-conscious, with oxygen saturations below 40 and survived. Most of the Everest records, including summits without oxygen, are held by Sherpas. Every foreign climber will have experienced some degree of mountain sickness: a thumping headache, blurred vision, nausea, and weakness, only to look up and witness a Sherpa bouncing past them carrying 40 kilogram loads as if they were on a Sunday stroll. Their internal mechanics, from the cellular level to the size of their lungs, are tuned like a Le Mans supercar.

Aaron Huey: It's like having Michael Jordan or LeBron James serving you cereal in bed while you're still in your sleeping bag because these guys, they really are some of the best athletes in the world and they are spooning this dude sugar.

Francis: Sherpas produce 30% more power than lowlanders at altitude. They have more capillaries per square centimeter of muscle than lowland climbers. They have bigger chests, greater lung capacity, as well as higher measures of all lung physiology, like peak flow. Remember HPV? It just isn't seen in the same way in Sherpa. Like mountain goats or yaks that live at altitude, Sherpa lungs just don't seem to misinterpret hypoxia and precipitate the same counterproductive tightening of the blood vessels. A lowlander's heart and major blood vessels start remodeling, i.e. changing function and shape, both in the short term and long term at altitude, but Sherpa hearts don't show these adverse changes. Lowlander cardiopulmonary dynamics change dramatically as they ascend from sea level to altitude and start to acclimatize, whereas Sherpa physiology remains remarkably similar at all levels. They are far, far less likely to develop altitude sickness, with fewer heart and breathing problems, and better sleep at altitude. Lowlander basal metabolic rate increases at altitude, which is why so many climbers lose weight. But Sherpa metabolic rate is unaffected and weight loss is not reported, with some even putting on weight with all the high-energy food you eat on a climb. They have higher levels of nitric oxide, which keeps blood vessels open and avoids high-altitude pulmonary and cerebral edema. They have better blood flow to their brain above 8,000 meters, reassuringly known as the Death Zone, and pregnant Sherpa don't experience the same complications of pregnancy. They have healthier babies and lower infant mortality. The crazy thing is they don't have that thick ragu-like blood with a high hematocrit. In fact, their hemoglobin is lower than a lowlanders.

Mitochondria, you've no doubt heard referred to as the power stations generating energy inside cells. They're actually found in lower concentrations in Sherpa than in lowlanders.

So this doesn't make any sense. They've got lower levels of hemoglobin and lower concentrations of mitochondria. How are they doing so much better than everyone else? Because the answer isn't in increasing oxygen delivery. It's in actually changing the way oxygen is used and this is something that takes thousands of years to select out. Sherpa muscles, both the heart and skeletal muscles, prioritize the use of carbohydrates over fats. You've no doubt heard the hype surrounding zero-carb, ketogenic diets, so you might know that muscles get their energy from two main sources: sugars and fat. In most people, fat is preferentially used in fasting states and has lots of energy, but the process of burning it requires more oxygen than burning carbohydrates. In fact, per oxygen molecule, adenosine triphosphate yield is 25% to 50% higher using glucose as a substrate rather than fat. Therefore, by preferentially using sugars, the Sherpa muscles just need far less oxygen, and what's more, their mitochondria are more efficient. Us lowland dweebs have got the equivalent of a two-stroke engine, whereas Sherpas are running high-tech hybrids.

Phosphocreatine can be used as an energy supply when ATP is scarce and lowlander levels of phosphocreatine go down as we ascend, but Sherpa levels actually increase. Researchers stated that it was almost as if they became healthier as they ascended to the altitudes for which they were evolved. There's much we still don't understand and only a handful of genes have been identified, but there are probably many, many more that contribute. In 2014, a team from UC-Berkeley published the fascinating finding that a gene responsible for the high-altitude adaptation of hemoglobin amongst the Sherpas, an EPAS1 variant nicknamed the "superathlete" gene came wholesale from the Denisovans. The Denisovans were a subspecies of human rather like the Neanderthals, and just like Neanderthals, our ancestors bred with the Denisovans. The Han Chinese also inherited the EPAS1 variant. But as they didn't live at altitude, there was no advantage to having the gene, and hence, it was lost, but the Sherpa kept it going.

There are other high-altitude communities in Ethiopia and the Andes, but the Himalayan plateau has been continually inhabited for about 30,000 years. What I love about these findings is that the doctors and scientists that undertook this work have demonstrated, as clear as day, evolution that's taken place in fairly recent history. Much of the information in this video is from research published by the extreme Everest team based at UCL, who have done extensive work in the field and used data from high altitude to help everyday patients with hypoxia in intensive care. The avalanche of 2014, an earthquake in 2015 were two horrendous tragedies for the region, claiming the lives of many Sherpa along with thousands more Nepalese. They've shown a much needed light on the often exploitative conditions under which many Nepalese work, and the risks they endure to provide for their families by taking wealthy Westerners to the summit. Nepal is a breathtakingly beautiful country with the warmest people I've ever met.

Please do check out some of the links below [on the YouTube site]. Don't forget to let me know what you thought of the video. I'll end with some Star Wars trivia. I bet you didn't think that anybody could link Star Wars, Nepal, and Tibet. Well, you'd be wrong, because in Return of the Jedi, the Ewoks language is actually Tibetan with a sprinkling of Nepalese. Were the diminutive and resourceful Ewoks based on the Sherpa? The answer is no.

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