Early humans apparently mated outside of their species, particularly with the Denisovans, not just once but at least twice. An early species of hominins, the Denisovans were closely related to neanderthals.
Denisovans lived across Asia and have been discovered only in recent time.
A new study published in Cell shows that there are two different regions in Asia where humans contain the Denisovan DNA. This finding indicates that the Denosivans had sexual encounter with humans on two occasions.
Scientists compared the Denisovan genome to 5,600 whole-genome sequences of people from Europe, Asia, North and South America, and Oceania. Results from the comparison show two different populations of Denisovans, one in Asia and one in Oceania.
A Denisovan population was already known to live in Oceania. People from Papua New Guinea were found to contain about 5 percent Denisovan ancestry.
The new population of Denisovans is found to be from East Asia, which includes the Han Chinese, Chinese Dai, and Japanese people. They were a much closer match for Denisovan DNA than the Papuan people.
Unlike in Papua New Guinea, the amount of Denisovan DNA found in modern Chinese and Japanese populations is only 0.2 percent. Even though Papuan people ended up with more Denisovan DNA, East Asian DNA more closely resembled Denisovan DNA.
Also present in the findings is the discovery that the Neanderthal DNA found in the human genome is homogenous, which leads to the conclusion that early humans mated with a single population of Neanderthals, unlike how they mated with the Denisovans. Results from the study suggest that Neanderthals and Denisovans weren't as different from humans as previously thought, especially since the humans mated with both species.
Denisovans were discovered in late 2000s when researchers found a piece of a pinky finger, a toe bone, and a tooth in Denisova Cave in Siberia. It wasn't until 2010 when it was discovered that those remains didn't belong to any humans or Neanderthals but to an entirely different species of hominin.
After this discovery, scientists began searching through DNA for traces of interbreeding between humans and Denisovans. Humans were previously found to have interbred with Neanderthals through DNA analysis, despite conventional knowledge saying otherwise.
This analysis led to the discovery of Denisovan DNA in around 5 percent of some Australiasians, especially in people from Papua New Guinea. This shows that humans had mated with Denisovans 50,000 ago or more.
Scientists were able to extract an almost complete Denisovan genome from the remains that were found.