Carl Zimmer in the New York Times:
In the hearts of evolutionary biologists, mountains occupy a special place. It’s not just their physical majesty: mountains also have an unmatched power to drive human evolution. Starting tens of thousands of years ago, people moved to high altitudes, and there they experienced natural selection that has reworked their biology.
“This is the most extreme example in humans that you can find,” said Rasmus Nielsen, an evolutionary biologist at the University of California at Berkeley.
Humans have adapted to mountainous environments just as Charles Darwin predicted. To discover how this occurred, scientists are now examining the DNA of people who scaled mountains in different parts of the world.
“There’s this beautiful experiment in natural selection going on,” says Anna Di Rienzo, a professor of human genetics at the University of Chicago. “You can really ask questions central to evolutionary biology.”
When people from low elevations climb to higher ones, they start struggling for oxygen. At 12,000 feet, each breath delivers only 60 percent of the oxygen that the same breath would at sea level. Even a slow walk can be exhausting, because the body can get so little fuel.
In the face of this stress, people respond in several ways.