Early humans didn't just mate with Neanderthals during human evolution, but with Denisovans also. Denisovans are an extinct group of early human species.
Researchers from Uppsala University have found that people in East Asia share genetic material with Denisovans. Denisovans got their names from the cave in Siberia where they were first found.
The new study covers a larger part of the world than earlier studies, researchers say.
Hybridization happened at several points in evolution, the genetic traces of which can be found in several places in the world.
Mattias Jakobsson, a professor of evolution biology at Uppsala University's Evolutionary Biology Centre in Sweden, conducted the new research with Pontus Skoglund. He stated in a press release that more events like that will probably be uncovered.
Previous studies have found two separate hybridization events happened between archaic humans, which are different from modern humans in both genetics and morphology, and the ancestors of modern humans after their emergence from Africa, according to researchers.
There was the hybridization between Neanderthals and the ancestors of modern humans outside of Africa and hybridization between Denisovans and the ancestors of indigenous Oceanians.
The Uppsala scientists found that hybridization also happened on the East Asian mainland. The Denisova-related gene variants were found in Southeast Asia and Oceania but not in Europe and America. Researchers now suggest that hybridization with the Denisova man happened about 20,000 to 40,000 years ago, but could also have been earlier.
This, they say, is long after the branch that became modern humans split off from the branch that led to Neandertals and Denisovans some 300,000 to 500,000 years ago.
The new study is based on DNA extracted from a 40,000-year-old Denisovan finger bone that was found in Siberian Russia's Altai Mountains in 2008.
The Uppsala researchers found that people from mainly Southeast Asia have a higher proportion of Denisova-related genetic variants than people from other parts of the world such as Europe, America, West and Central Asia and Africa.
Jakobsson says the findings show that gene flow from archaic human groups also occurred on the Asian mainland.
While we can see that genetic material of archaic humans lives on to a greater extent than what was previously thought, we still know very little about the history of these groups and when their contacts with modern humans occurred, Skoglund says in a press release.
With more complete genomes from modern humans and more analyses of fossil material, it will be possible to describe our prehistory with considerably greater accuracy and richer detail, Jakobsson says.
You can read more about the study in the Proceedings of the National Academy of Sciences.