Neanderthal Genome Reveals Long History of Interbreeding with Early Humans

We're learning more than ever about ancient Neanderthals, thanks to the most complete sequence to date of the Neanderthal genome. The ancient DNA reveals a long history of Neanderthals interbreeding among at least four different types of early humans living in Europe and Asia.

The latest findings were discovered thanks to a woman's toe bone that dates back 50,000 years. The researchers generated a high-quality sequence of the Neanderthal genome and then compared it with the genomes of modern humans and a recently recognized group of early humans called Denisovans.

It turns out that Neanderthals and Denisovans are very closely related, though both of the groups eventually died out. Their common ancestor actually split off from the ancestors of modern humans about 400,000 years ago while Neanderthals and Denisovans split about 300,000 years ago. Not only that, but it turns out that both Denisovans and Neanderthals occasionally interbred with modern humans. In fact, about 1.5 and 2.1 percent of the genomes of modern non-Africans can be traced to Neanderthals.

Yet Neanderthals weren't the only ones to leave traces of their genetic material behind. Denisovans also left their traces in modern humans, though only in some Oceanic and Asian populations. The genomes of Australian aborigines, New Guineans and some Pacific Islanders are about 6 percent Denisovan genes. In addition, the genomes of Han Chinese and other mainland Asian populations, as well as of native Americans, contain about .2 percent Denisovan genes.

"The paper really shows that the history of humans and hominins during this period was very complicated," said Montgomery Slatkin, one of the researchers, in a news release. "There was a lot of interbreeding that we know about and probably other interbreeding we haven't yet discovered."

The researchers also found that populations of Denisovans and Neanderthals were likely small and that inbreeding may have been more common. The findings could tell researchers a bit more about the social relations and history of these two ancient groups. Currently, the researchers are looking at these groups a bit more closely-especially now that they know they were a part of the creation of modern humans.

"We don't know if interbreeding took place once, where a group of Neanderthals got mixed in with modern humans and it didn't happen again, or whether groups lived side by side and there was interbreeding over a prolonged period," said Slatkin in a news release.

The findings are published in the journal Nature.