AncientPages.com - Modern humans co-existed and interbred not only with Neanderthals, but also with a related archaic population, we known today as Denisovans.
Researchers unexpectedly discovered two separate episodes of Denisovan genetic intermixing.
They determined that the genomes of two groups of modern humans with Denisovan ancestry - individuals from Oceania and individuals from East Asia - are uniquely different, indicating that there were two separate episodes of Denisovan admixture.
"What was known already was that Oceanian individuals, notably Papuan individuals, have significant amounts of Denisovan ancestry," says senior author Sharon Browning, a research professor of biostatistics, University of Washington School of Public Health.
The genomes of modern Papuan individuals contain approximately 5% Denisovan ancestry."
It was also known that Denisovan ancestry is present to a lesser degree throughout Asia and it was achieved through migration, coming from Oceanian populations.
"But in this new work with East Asians, we find a second set of Denisovan ancestry that we do not find in the South Asians and Papuans," Browning said. "This Denisovan ancestry in East Asians seems to be something they acquired themselves."
This graphical abstract shows two waves of Denisovan ancestry have shaped present-day humans. Credit: Browning et al./Cell
Researchers studied more than 5,600 whole-genome sequences from individuals from Europe, Asia, America, and Oceania and compared them to the Denisovan genome, Browning and colleagues determined that the Denisovan genome is more closely related to the modern East Asian population than to modern Papuans. 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," the researcher said.
"The assumption is that admixing with Denisovans occurred fairly quickly after humans moved out of Africa, around 50,000 years ago, but we do not know where in terms of location," Browning said.
She hypothesizes that perhaps the ancestors of Oceanians admixed with a southern group of Denisovans while the ancestors of East Asians admixed with a northern group.
The researchers plan further studies on Asian populations and others throughout the world, including Native Americans and Africans.