Homo sapiens managed to settle in this unforgiving landscape around 30,000 to 40,000 years ago, and around 10,000 years ago, they brought their dogs. While that might suggest our species is especially rugged or adaptable, we now know that neither the people nor their pets toughed it out alone—both cribbed DNA notes from other species in order to adapt. Either before, during, or shortly after their migration to the plateau, H. sapiens got friendly with Denisovans, while their domesticated dogs interbred with Tibetan wolves. And from those hybridizations, both picked up adaptive variants of the EPAS1 gene, which encode version of the protein that help their bodies, and especially their blood, cope with lower levels of oxygen. “You have the exact same [phenomenon] between dogs and wolves as you have between humans and Denisovans,” explains Rasmus Nielsen, a geneticist with the University of California, Berkeley. “It’s so cool.”
Wolves are not alone, of course, in their penchant for mating with more distant kin. Thanks to similar genetic echoes of hybridization, scientists know brown bears cozied up to cave bears before the latter went extinct (and they continue to romp with polar bears), elephant species interbred frequently back in the time of mammoths, and cats apparently fornicate with other felines at almost any opportunity. “The more genomes that have been sequenced from the more different lineages and species and places in the world, the more we see that when things interact with each other in space and can interbreed, they do,” says Beth Shapiro, an evolutionary biologist at the University of California, Santa Cruz, who worked with Nielsen on the Tibetan dogs paper.