Ancient humans weren't against knocking boots with other species: We know they had sex with Neanderthals. We also know they mated with the mysterious Denisovans, as some Australasians (those from Papua New Guinea in particular) have 5% Denisovan DNA. But a "breakthrough" study shows the interbreeding wasn't limited to those two instances. While looking for ancient DNA in the genomes of 5,600 living humans, a team at the University of Washington in Seattle came across evidence of a third interbreeding event, reports New Scientist. A smaller contribution of Denisovan DNA in Han Chinese, Chinese Dai, and Japanese people—about 0.2% of their genome—suggests humans mixed with a distinct population of Denisovans in not one but two locations: Indonesia or Australasia and East Asia.
Though the only four Denisovan fossils that have been found come from the same cave in Siberia, the research published in the journal Cell shows Denisovans were spread across Asia and "suggests that at least in some instances, Denisovans and modern humans were willing to live in proximity and interact," lead author Sharon Browning says. Her research also backs the theory that there was a single "wave" of interbreeding between humans and one population of Neanderthals, reports the Atlantic. But Browning couldn't link other ancient DNA found in living humans to Neanderthals or Denisovans, suggesting humans may have mated with hominins we haven't even discovered yet. Harvard geneticist David Reich, who was not involved in the research, says the finding of "a definite third interbreeding event" makes this "a breakthrough paper," per the Washington Post. (Here's how a bit of cave dirt changed archaeology.)