By Los Angeles Times, adapted by Newsela staff
A Tibetan girl poses in front of one of the glaciers on the Tibetan plateau. High-altitude Tibet is known as the “rooftop of the world.”
Forget climbing Mount Everest—for most humans, surviving on the harsh Tibetan plateau would be challenge enough. Tibetan people, however, have thrived there for thousands of years. A new study
says that’s thanks to a gene they inherited from an ancient human relative that died out—became extinct—tens of thousands of years ago.
The study shows that the extinct people known as Denisovans and modern-day Tibetans share an unusual gene. It is that gene, scientists think, that gives Tibetans an advantage over lowlanders at
high altitudes. No one knew the Denisovans ever roamed the Earth until four years ago, when an unusual finger bone was unearthed in southern Siberia. The bone exhibited genetic similarities to both modern humans and our extinct Neanderthal relatives. However, it was different enough to be considered a distinct species.
Like Neanderthals, Denisovans mated with other kinds of humans, scientists soon discovered. Modern-day Papua New Guineans share 5 percent of their genetic makeup with the Denisovans.
Now it appears that Tibetans can also trace part of their ancestry to this mysterious group.
Few Share The Altitude Gene
In the new study, which was published on Wednesday, scientists collected blood samples from 40 Tibetans. All those samples contained EPAS1, the gene that makes Tibetans so well-suited for life at high altitude. The scientists then looked at blood samples from 1,000 individuals of 26 population types. They found the high-altitude gene in only two of 40 Han Chinese people—the largest ethnic group in China—and in no one else. “Natural selection by itself could not explain that pattern,” said biologist Rasmus Nielsen, an author of the study. The EPAS1 gene “was too different from anything else we saw in other populations.” So they investigated whether the gene might have been imported from extinct Neanderthals or Denisovans.
Bingo—they found a match: the Denisovans. But how did the gene end up in modern Tibetans? The scientists used computer models to test two different theories. Were Denisovans and Tibetans descended from a common ancestor that gave the gene to both? Or did humans acquire the gene by mating with Denisovans? How Did The Gene Get There? Early humans and Denisovans probably separated around half a million years ago. It’s very unlikely,
Nielsen said, that the gene could be maintained in both populations for so long.
Alternatively, the gene could have entered the Tibetan gene pool more recently through mating. Once transferred, the gene would have spread rapidly in the Tibetan population. Those who had
it would be far more likely to survive at high altitudes, and would pass the gene on to their descendants. “Genetically, Han Chinese and Tibetans are very similar,” Nielsen said. “But for this particular
gene, they are extremely” distinct from each other, he said. It’s “something you only see with very strong or very recent selection,” which causes certain genes to spread through a population.
The reason Tibetans need EPAS1 is that their mountainous home lies about 15,000 feet above sea level, on average. Up there, the air contains 40 percent less oxygen than low elevations.
Scientists Still Have Lots Of Questions
Previous studies had already identified the importance of EPAS1. However, scientists still don’t know exactly what the gene does. They know only that it leads to lower levels of hemoglobin—the
oxygen-carrying protein in blood—in Tibetans who live at high altitude compared with people from low elevations. That may sound like the opposite of what you’d expect, said Nielsen. After all, wouldn’t you want more oxygen, and thus, more hemoglobin to deliver it? People without the gene, however, tend to
“overreact” at high altitudes. At high elevations, “we’ll start to produce a lot of red blood cells,” he said, speaking for himself
and other non-Tibetans. Too many, in fact. “That will expose us to various diseases” like high blood pressure and increased risk of stroke. “There are very negative fitness effects of having too
many red blood cells, and the Tibetans avoid them.”
So how do Tibetans get more oxygen? Presumably they don’t, Nielsen said, and scientists are still trying to understand just what is going on. However, one thing is now clear: They owe their extraordinary fitness to a rogue gene introduced into their gene pools by those long-lost cousins, the Denisovans.
Let’s Expand The Search
Anthropologist Abigail Bigham studies human beings and their ancestors. She said the search for Denisovan DNA should now extend to other groups. “When they looked in Han Chinese, they saw it in only two individuals,” Bigham said. However, “there are 49 other ethnic minorities in China that have different genetic backgrounds.“ Those groups and “other populations in Central Asia or East Asia” would have been “interesting to look
at as well.”
In any case, she said, the new study helps reshape the way scientists think about our extinct relatives. It is part of a growing body of work that demonstrates that they were important to our
own genetic development. For a long time, most scientists believed Neanderthals and Denisovans had nothing to do with modern humans. Now they realize that’s not the case. Indeed, these species are responsible for introducing some of the genetic diversity that allowed people to adapt to unique environments. “We’ve come full circle,” Bigham said. “Not only has there been interbreeding, but in fact that interbreeding has led to important” physical changes.
A Tibetan girl poses in front of one of the glaciers on the Tibetan plateau. High-altitude Tibet is known as the “rooftop of the world.”
Forget climbing Mount Everest—for most humans, surviving on the harsh Tibetan plateau would be challenge enough. Tibetan people, however, have thrived there for thousands of years. A new study
says that’s thanks to a gene they inherited from an ancient human relative that died out—became extinct—tens of thousands of years ago.
The study shows that the extinct people known as Denisovans and modern-day Tibetans share an unusual gene. It is that gene, scientists think, that gives Tibetans an advantage over lowlanders at
high altitudes. No one knew the Denisovans ever roamed the Earth until four years ago, when an unusual finger bone was unearthed in southern Siberia. The bone exhibited genetic similarities to both modern humans and our extinct Neanderthal relatives. However, it was different enough to be considered a distinct species.
Like Neanderthals, Denisovans mated with other kinds of humans, scientists soon discovered. Modern-day Papua New Guineans share 5 percent of their genetic makeup with the Denisovans.
Now it appears that Tibetans can also trace part of their ancestry to this mysterious group.
Few Share The Altitude Gene
In the new study, which was published on Wednesday, scientists collected blood samples from 40 Tibetans. All those samples contained EPAS1, the gene that makes Tibetans so well-suited for life at high altitude. The scientists then looked at blood samples from 1,000 individuals of 26 population types. They found the high-altitude gene in only two of 40 Han Chinese people—the largest ethnic group in China—and in no one else. “Natural selection by itself could not explain that pattern,” said biologist Rasmus Nielsen, an author of the study. The EPAS1 gene “was too different from anything else we saw in other populations.” So they investigated whether the gene might have been imported from extinct Neanderthals or Denisovans.
Bingo—they found a match: the Denisovans. But how did the gene end up in modern Tibetans? The scientists used computer models to test two different theories. Were Denisovans and Tibetans descended from a common ancestor that gave the gene to both? Or did humans acquire the gene by mating with Denisovans? How Did The Gene Get There? Early humans and Denisovans probably separated around half a million years ago. It’s very unlikely,
Nielsen said, that the gene could be maintained in both populations for so long.
Alternatively, the gene could have entered the Tibetan gene pool more recently through mating. Once transferred, the gene would have spread rapidly in the Tibetan population. Those who had
it would be far more likely to survive at high altitudes, and would pass the gene on to their descendants. “Genetically, Han Chinese and Tibetans are very similar,” Nielsen said. “But for this particular
gene, they are extremely” distinct from each other, he said. It’s “something you only see with very strong or very recent selection,” which causes certain genes to spread through a population.
The reason Tibetans need EPAS1 is that their mountainous home lies about 15,000 feet above sea level, on average. Up there, the air contains 40 percent less oxygen than low elevations.
Scientists Still Have Lots Of Questions
Previous studies had already identified the importance of EPAS1. However, scientists still don’t know exactly what the gene does. They know only that it leads to lower levels of hemoglobin—the
oxygen-carrying protein in blood—in Tibetans who live at high altitude compared with people from low elevations. That may sound like the opposite of what you’d expect, said Nielsen. After all, wouldn’t you want more oxygen, and thus, more hemoglobin to deliver it? People without the gene, however, tend to
“overreact” at high altitudes. At high elevations, “we’ll start to produce a lot of red blood cells,” he said, speaking for himself
and other non-Tibetans. Too many, in fact. “That will expose us to various diseases” like high blood pressure and increased risk of stroke. “There are very negative fitness effects of having too
many red blood cells, and the Tibetans avoid them.”
So how do Tibetans get more oxygen? Presumably they don’t, Nielsen said, and scientists are still trying to understand just what is going on. However, one thing is now clear: They owe their extraordinary fitness to a rogue gene introduced into their gene pools by those long-lost cousins, the Denisovans.
Let’s Expand The Search
Anthropologist Abigail Bigham studies human beings and their ancestors. She said the search for Denisovan DNA should now extend to other groups. “When they looked in Han Chinese, they saw it in only two individuals,” Bigham said. However, “there are 49 other ethnic minorities in China that have different genetic backgrounds.“ Those groups and “other populations in Central Asia or East Asia” would have been “interesting to look
at as well.”
In any case, she said, the new study helps reshape the way scientists think about our extinct relatives. It is part of a growing body of work that demonstrates that they were important to our
own genetic development. For a long time, most scientists believed Neanderthals and Denisovans had nothing to do with modern humans. Now they realize that’s not the case. Indeed, these species are responsible for introducing some of the genetic diversity that allowed people to adapt to unique environments. “We’ve come full circle,” Bigham said. “Not only has there been interbreeding, but in fact that interbreeding has led to important” physical changes.