Mixing may have been common among groups of early humans.

Analysis of a bone found in a Siberian cave shows that a 90,000-year-old female was half Neanderthal and half Denisovan. The discovery is the first of its kind to find an individual who was a first-generation offspring of different prehistoric groups of humans.

“To find a first-generation person of mixed ancestry from these groups is absolutely extraordinary,” population geneticist Pontus Skoglund at the Francis Crick Institute in London, tells Nature. “It’s really great science coupled with a little bit of luck.”

The team was led by palaeogeneticists Viviane Slon and Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who put together the genome analysis from a bone fragment found in the Denisova cave in Siberia.

According to CBS:

Past genetic studies have shown interbreeding between the two groups, as well as with our own species, which left a trace in the DNA of today’s people. But the new study is the first to identify a first-generation child with Neanderthal and Denisovan parents.

“It’s fascinating to find direct evidence of this mixing going on,” said Svante Paabo, one of the study’s lead authors.

Paabo said he was surprised by the discovery, given how relatively few remains of our evolutionary relatives have been found around the world.

The genetic analysis shows the female’s mother was a Neanderthal, while the father came from the Denisovan group. Nature reports:

The results convincingly demonstrate that the specimen is indeed a first-generation hybrid, says Kelley Harris, a population geneticist at the University of Washington in Seattle who has studied hybridization between early humans and Neanderthals. Skoglund agrees: “It’s a really clear-cut case,” he says. “I think it’s going to go into the textbooks right away.”

Harris says that sexual encounters between Neanderthals and Denisovans might have been quite common. “The number of pure Denisovan bones that have been found I can count on one hand,” she says — so the fact that a hybrid has already been discovered suggests that such offspring could have been widespread.