“We analyzed all of the genomes searching for sections of DNA that looked like they came from Denisovans,” she said. “When we compared pieces of DNA from the Papuans against the Denisovan genome, many sequences were similar enough to declare a match, but some of the DNA sequences in the East Asians, notably Han Chinese, Chinese Dai, and Japanese, were a much closer match with the Denisovan.”

This study suggests that anatomically modern humans interbred with Denisovans very soon after leaving Africa somewhere between 200,000 to 50,000 years ago, and that this interbreeding happened in two pulses. Browning’s team isn’t exactly sure where these trists took place, but they suspect a southern group of Denisovans mated with the ancestors of Oceanians and a northern group mated with ancestors of East Asians. More evidence will be required to push this research forward.

Interestingly, the same research also tells us something new about Neanderthals, who also interbred with modern humans. Previous evidence suggested humans got it on with multiple Neanderthal populations, owing to different amounts of Neanderthal DNA when comparing living individuals of European and Asian descent. But Browning found tremendous homogeneity in the Neanderthal sequences analyzed, leading them to conclude that early modern humans mated with a single Neanderthal population, and that the discrepancies seen in living Europeans and Asians in terms of Neanderthal DNA must’ve been caused by something else, like European humans interbreeding with other groups of humans, i.e. those coming out of Africa, with zero Neanderthal DNA. That’s kind of a shocker, and more evidence will be required to suss this out.

“[Browning et al.] have trawled modern human genomes to look for signs of Denisovan DNA, and have discovered that the Denisovan DNA in Asia derives from two different sources, one like that found in modern Australasians (in southern Asia), the other more like the Siberian version (in eastern Asia),” Chris Stringer, a paleoanthropologist at the Natural History Museum in London who wasn’t involved in the new study, told Gizmodo. “This adds another level of complexity to the dispersal history of modern humans as they moved across Asia in confirming that there were at least two distinct Denisovan populations, and that there was a more complicated history of interactions with them.”

In the future, Stringer said it would be valuable to put a time sequence on the various interbreeding events with Neanderthal and Denisovans. “Hopefully this will be possible one day,” he said.

“I think the coolest thing with this work is that they show that there were at least two distinct populations of the Denisovans in the past, and that both these populations met with modern humans and mixed with them,” Svante Pääbo, a geneticist at the Max Planck Institute for Evolutionary Anthropology, told Gizmodo. “This finding makes it very likely that Denisovans were widespread in Asia as modern humans appeared on the scene.”

Anne Stone, an anthropological geneticist at University State University, thinks the new study “was really well done,” and was most surprised to see the researchers tease out the relatively small amounts of Denisovan-derived DNA segments and uncover the signatures of the two genetic mixing events.

“Interestingly, they also find that modern human admixture with Neanderthals may have only happened once, rather than twice as some have posited to account for a higher Neanderthal component in Asia compared with Europe,” she told Gizmodo, adding that the study is helping us understand the extent of interbreeding among early modern humans and other types of humans outside of Africa.

A huge limitation of this study, of course, is that Browning’s team had only one Denisovan genome to work with, and a partial one at that. We have no reason to believe that this single sample is tarnished or weird in any way, but it would be super helpful to find additional Denisovan DNA. The search continues, but as this study shows, human history is more complicated—and diverse—than we could have ever imagined.