In the Altai mountains of southern Siberia, there's a cave that was inhabited for millennia. It's called Denisova, and it shelters something remarkable: the bones of different types of ancient human relatives.
Back in 2010, researchers analyzed a fossilized pinky finger bone found in the cave, and discovered a whole new branch of the human family tree. They were dubbed Denisovans: a group of now-extinct hominins genetically different from either Neanderthals or modern humans, who were roaming the planet at the same time.
After that discovery, researchers kept sifting through thousands of bone fragments in the cave, many of them from animals, until they found one that seemed like it could be from some kind of human relative. It turned out to belong to a young female who lived 90,000 years ago, whom they call Denisova 11.
Now they have sequenced her genome, and as they announced in Nature on Wednesday, they found something quite surprising: She had a Neanderthal for a mother and a Denisovan for a father.
"We then have very direct evidence – almost caught in the act, so to say – of mixing with each other," says Svante Pääbo, a geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led the research.