We rarely portray our close relatives’ Neanderthals as telegenic. Museum exhibits give them wild tangles of hair, and Hollywood reduces them to grunting unsophisticated. Their skulls suggest broad faces, as well as tiny chins and jutting brows. However, to mock Neanderthals is to mock ourselves: Homo sapiens had lots of sex with Homo Neandertahlensis. Neanderthal genes supply between 1% and 4% of the genome in people from homelands on several continents, from Britain to Japan to Colombia.
DNA from another human-like primate, the Denisovans, lurks in modern genomes, as well. A molar and a chip of pinkie bone found in a Siberian cave provide what little information we have about this mysterious species. DNA extracted from the fragments previously revealed cross-species breeding. Still, a new study in the journal Cell shows that the ancient hanky-panky did not stop in Siberia: Humans that traveled across South Asia mated with a separate group of Denisovans, too.
David Reich, a person who studies ancient DNA at Harvard University and was not involved with the study, said:
“This is a breakthrough paper. It is a definite third interbreeding event, which is one that adds to the previously known Denisovan and Neanderthal mixtures.”
Humans, as well as Neanderthals, were divided into separate groups as far back as 765,000 years ago. Denisovans and Neanderthals were closer cousins that split more recently and then vanished – maybe because we absorbed their lineages.
A team of scientists led by the University of Washington biostatistician named Sharon R. Browning took an approach that Reich called a “technical tour de force.” In that new study, Browning and her colleagues examined more than 5,500 genomes of modern humans from Europe, as well as from Asia and Oceania, looking for any possible archaic DNA. Browning said:
“We are looking for a segment of DNA in an individual which look quite different from the rest of the variation in the population.”
When the team fished out the DNA variations, the researchers have matched the segments to Denisovan and Neanderthal sequences, which are known from samples in the Altai Mountains in Siberia.
All of the groups that were studied, from British and Bengali people to Peruvians and Puerto Ricans, had a dense cluster which closely matched the Neanderthals from the Altai Mountains. Also, some of the populations had a cluster which matched the Altai Denisovans, which was particularly pronounced in East Asians.
The surprise was a third cluster – not like the DNA of Neanderthal and just partially resembling the Altai Denisovans. The authors concluded that this was a second, as well as the separate pulse of Denisovans genes into the DNA blender.
Browning said: “The geography is quite suggestive.” The authors also hypothesize that, as ancestral humans migrated eastward,Remove featured imagethey came across two different Denisovan populations. One pulse which appears to the north shows up in people from China, as well as Japan and Vietnam.
The other Denisovan pulse appears to the south. Browning said:
“Perhaps, it was down in the southeast corner of Asia. It could probably have been on an island en route to Papua New Guinea, but we do not know that.”
Reich said that he would not be surprised if some methods that are similar to this one revealed additional mixtures. Considering the extensive range of archaic groups across Eurasia, he said: “I am sure there are others too.”
Browning is planning to continue to hunt for additional mixtures. He will include people of African descent that were excluded from this study. Reich also said:
“We are interested in some other populations all over the world, especially Africa.”
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