Humans and Denisovans did it… twice!

Modern humans coexisted and mated not only with Neanderthals, but with another archaic human species, the mysterious Denisovans. The results of this study were published in the journal Cell.

Large faces, tiny chins and prominent eyebrows. The appearance of Neanderthals is often mocked. But making fun of Neanderthals is like making fun of ourselves: Homo sapiens had a lot of sex with Homo neanderthalensis. The genes of Neanderthals represent today between 1 and 4% of our genome. But that’s not all. The DNA of other archaic humans, the Denisovans, is also hidden in modern genomes.

A few years ago in southern Siberia were found two molars and a phalanx of children about 80,000 – 50,000 years old, more precisely in an Altai cave. Thanks to the well-preserved DNA and the contributions of the genetic sciences, the researchers were able to identify a new and mysterious human group: the Denisovans. By developing a new method of genome analysis, researchers at the University of Washington in Seattle, unexpectedly discovered two distinct episodes of genetic mixing between the Denisovians and modern humans. This suggests a more diverse genetic history than previously thought.

The researchers explain in the study to have examined more than 5,500 modern human genomes from Europe, Asia and Oceania, looking for possible archaic DNA. After locating variations in the DNAs, the scientists then compared these segments to the Denisovan and Neanderthal sequences, known from samples taken in the Altai Mountains.

Previous research has shown that while the Denisovans shared a common origin with Neanderthals, they were almost as distinct from Neanderthals as the Neanderthals were from modern humans. Previous work has also shown that the Denisovians have contributed to the DNA of many modern human groups.

They donated a portion of their DNA to about 5% of the genomes of the Oceanian populations, and some 0.2% to the genomes of continental Asians and Native Americans. Scientists then assumed that this Denisovan DNA found in modern humans in Asia came from the cross between the Denisovans and the Oceanians who had migrated to Asia. What the study determines today is that there have been two separate episodes of miscegenation.

“I was surprised to find that there were finally two very different groups of Denisovians who had contributed to the DNA of modern humans – it was not something I expected to see,” notes Sharon Browning, geneticist at the University of Washington. The researchers suggest that the ancestors of the Oceanians crossed with a group of Southern Denisovians, while the ancestors of the East Asians mixed with a group from the North.

Thus there would have been at least three examples of modern human crosses with archaic human populations — one cross with Neanderthals and two with Denisovans.

Scientists now plan to look for more signs of modern human crosses and other archaic lineages in other populations around the world. This could be particularly the case in Africa, but since the climate is warmer, no one has yet found archaic human fossils with enough DNA for sequencing.

Shakes Gilles

Editor of The Talking Democrat. He enjoys bike riding, kayaking and playing soccer. On a slow weekend, you'll find him with a book by the lake.