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This is Scientific American 60-Second Science. I'm Karen Hopkin. This'll just take a minute.

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When you hear the word "mutation," you may think of something destructive, or of Marvel's X-Men.

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But some mutations which are just differences in DNA can be historic.

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Take, for example, a genetic sequence found in the vast majority of people from Tibet.

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Millions of Tibetans spend their days at average elevations of nearly 15,000 feet,

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that's more than half the height of Mount Everest.

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Up there, the air is thin with 40 percent less oxygen than at sea level.

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That lack of O2 would leave most Westerners struggling for breath, but Tibetans seem to breathe easy.

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To find out how these highlanders cope, researchers compared the DNA of 90 Tibetans to that of people who are not altitude adapted.

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And they discovered a single change that prevents Tibetans' blood from becoming dangerously clogged with red blood cells, a response that can be deadly for non-native mountaineers.

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The finding is described in the journal Nature Genetics.

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This mutation appears to have originated just 8,000 years ago.

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But it's so advantageous that today nearly 90 percent of Tibetans have it.

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While it's virtually absent in even closely related lowland neighbors.

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The finding demonstrates that a really useful mutation will always rise to the top.

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Thanks for the minute, for Scientific American 60-Second Science. I'm Karen Hopkin.

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