The "Sherpa Phenomenon": Human Evolution at Work
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November 05, 2010

The "Sherpa Phenomenon": Human Evolution at Work

Appa-sherpa-18-fois-everest Scientists have long wondered why the sherpas of the Tibetan Highlands can negotiate with ease elevations that cause some humans to become life-threateningly ill. Tibetans live at altitudes of 13,000 feet, breathing air that has 40 percent less oxygen than is available at sea level, yet suffer very little mountain sickness. The reason, according to a team of biologists in China, is human evolution, in what may be the most recent and fastest instance detected so far.

Comparing the genomes of Tibetans and Han Chinese, the majority ethnic group in China, the biologists found that at least 30 genes had undergone evolutionary change in the Tibetans as they adapted to life on the high plateau. Tibetans and Han Chinese split apart as recently as 3,000 years ago, say the biologists, a group at the Beijing Genomics Institute led by Xin Yi and Jian Wang, according to recent reports in Science and the New York Times.

Elsewhere, researchers from the University of Utah School of Medicine and Qinghai University Medical School in the People's Republic of China found that thousands of years ago, Tibetan highlanders began to genetically adapt to prevent polycythemia (a process in which the body produces too many red blood cells in response to oxygen deprivation), as well as other health abnormalities such as swelling of the lungs and brain (edema) and hypertension of the lung vessels leading to eventual respiratory failure.

Even at elevations of 14,000 feet above sea level or higher, where the atmosphere contains much less oxygen than at sea level, most Tibetans do not overproduce red blood cells and do not develop lung or brain complications. The researchers found evidence that this might be related to at least 10 genes, two of which are specific genes strongly associated with hemoglobin, a molecule that transports oxygen in the blood.

High-altitude lung and brain complications threaten and even kill mountaineers who scale the world's tallest peaks. Others who find themselves at elevations significantly higher than where they normally live and work also can be stricken with the condition. Adaptations to living at higher altitudes have occurred in humans more than once, such as with people indigenous to the Andes Mountains in South America and people native to high altitude regions in the Ethiopian mountains in Africa.

But the Tibetans have evolved genes that others living at similar elevations have not developed, according to Lynn B. Jorde, Ph.D., professor and chair of human genetics at the U of U School of Medicine and a senior author on the study. "For the first time, we have genes that help explain that adaptation," Jorde said.

The study was undertaken after Josef T. Prchal, M.D., a hematologist and professor of internal medicine, approached Jorde about doing genetic analysis related to his research on polycythemia.

"What's unique about Tibetans is they don't develop high red blood cells counts," said Prchal, also a senior author on the study who has done research in Tibet. "If we can understand this, we can develop therapies for human disease."

Although much work remains, and there could be other physiological reasons for the Tibetans' ability to thrive at higher elevations, the researchers believe those 10 genes might have allowed the Tibetans to evolve more efficient metabolisms and not overproduce red blood cells in response to thinner air. The Tibetans also show higher levels of nitric oxide, a molecule that may help get more oxygen to tissues and prevent polycythemia.

"This might help make up for having fewer red blood cells," Jorde said. A detailed understanding of these changes may eventually lead to targeted therapies for common human maladies, including pulmonary hypertension and lung and brain edema, which affect people everywhere.

Casey Kazan via University of Utah

Comments

So much for the old "it takes thousands of generations to effect change in a people group" idea. This is pretty evidence (not proof, of course, but certainly evidence) that, yes indeed, it is quite possible that all of our myriad ethnic characteristics could have sprung up in only a few thousand years.

On another line of thought entirely, I wonder how well a Tibetan would handle a trip to the ISS. Some of the adaptations may make it easier to handle microgravity and other issues with space travel.

Very cool. I always thought that they survived better up there because of more red blood cells, but now it looks like it's a little more complicated than that.

I wonder if Tibetans have a harder time at sea level than people who're more adapted to living down there. Maybe the higher pressure and higher oxygen has some bad effects on them?

I was wondering something along the same lines. Just like the mountaineers experience lung and brain complications at high altitudes what complications would these Tibetans experience if exposed to lower elevations?

Not a bad thought, Joe. Probably the Tibetans suffer no ill effects -- I've little doubt that several have made the journey to live in Singapore or San Francisco -- but it's an idea worth examining.

after living at 7000 ft and taking an air plane to sea level - i felt an intoxication that lasted a number of days.

With regards to the claim that we have entered a new evolutionary phase, I'd have to say Biological evolution continues alongside our "technological" evolution. At a much slower or impeded rate...

The thing is, what hardships do our modern people face that would allow evolution to take place? These people live on top of a mountain, so they evolved the ability to breathe less oxygen.

But consider your standard city-faring folk. Speaking in general, they receive medical benefits and live to a ripe old age. Natural selection doesn't take place. The very weak are allowed to live and reproduce. They don't live in harsh environments so what would they evolve.. the ability to sit at a desk in a cubicle for extended period of time?

I say when it comes to biological evolution, we are our own worst enemies. We impede it.

Evolution never ceases to take place. Remember, "evolution is smarter than you."

Why is it considered evolution by you guys and not adaptation??? Yea humans adapt to all sorts of enviroment whether it be extreme hot, cold, high elevation. I personaly would like to see the fish that decided it wanted lungs and somehow made generations of its offspring want the same thing?? I actually didnt realize fish were that smart....

Adaption that occurs genetically and over different generations IS evolution jim bob. And you don't have to 'decide' to evolve. You just came accross every ignorant. Don't act like evolution isn't real just because your to scared to admit all the words in your ancient holy book aren't real. Maybe humans didn't evolve from apes (though they prob did), maybe they were 'divinely' created, but evolution exists stupid. Its science.

Adapting is not evolution..

Adaptation would be one of these people altering their personal biochemistry to survive better. Evolution, what is at play in the Tibetan population, is the trend toward the prevalence of genes that lead to better survival at these altitudes. This is developed over many generations and thousands of years. You could say that their genome has "adapted" over thousands of years. This, however, is confusing because it implies a choice. The gradual shift is a consequence of natural selection alone, no preconceived intention. Evolution is amazing!

We evolved from the animal world with the intelligence to build civilization. Funny how few seem to consider spiritual and consciousness evolution alongside the physiological, biochemical, environmental. I don't believe evolution stops for city dwellers or sherpas. We just need to adapt our intelligence to what is right in front of us, be it a mountain or the belly of the beast.

I believe it's adaptation, not evolution! Has anyone bothered to check the children of any Shirpas that have been born and raised at close to sea level? When a fence grows into a tree, the tree hasn't evolved, it has adapted. Environmental factors change biochemistry. Remove the environmental factor that is causing the change and organism will return to it's normal state in subsequent generations.

Big 'E' evolution is a fallacy and any conclusions based on that premise are false. An open mind is required to generate useful data and a constant drive to find causes for discrepancies in that data.

Genes are turned on or off by biochemical changes in the environment. Change the environment, change the genes.

Regarding whether Sherpas experience the opposite effect at sea level, I can possible give some personal 'evidence'.

My father was a full Sherpa (genetically speaking) and had exceptionally high blood pressure; so high in fact that he was told by one doctor he should be dead! As his blood pressure tests were all taken at low altitude (relatively), there is the possibility that his high blood pressure may have been due to his body being adapted to high altitude and therefore still behaving as if it were (the theory being that higher blood pressure allows more blood and therefore oxygen to circulate the body in a given time period). I also have high blood pressure (though am only half Sherpa).

This is of course a wholly unscientific observation and my family (or my father's side at least) may well just have high blood pressure as a medical condition, rather than as an adaptation. Still, it may be worth considering.

Great, fascinating study that sheds light on the amazing ability of the Sherpa.


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