It’s long been thought that the Tibetans acquired the genes for high-altitude tolerance through thousands of years of evolution. Now, an international team of scientists led by the University of California, Berkeley has shown that the Tibetans actually acquired the gene when their ancestors mated with an extinct human cousin, the Denisovans. Study leader Rasmus Nielsen says that this is quite different from the usual process of evolution.

"What’s different here is that the genetic variant didn’t come by mutation. It came from another species from interbreeding with another species. At some point there was a hybrid between Denisovans and modern humans. They could get the genetic variant that allowed them to live there by interbreeding with another species that was already adapted to that environment. It’s what population geneticists call adaptive integration."

He says that adaptive integration may have been more important in human evolution than previously thought.

"Now, we know that there was another process that was really important and maybe one of the keys to explain why humans could adapt to so many different environments so fast."