In the genome of an extinct species - Denisovans - unusual pieces of DNA were found, which, apparently, he got from some other group.
Perhaps this is evidence of the existence of a completely different species of hominins, still unknown to science. Or is it the first genetic data about one of the many species that we only know from fossils.
The new hominin left its traces in the genome of the Denisovan - an extinct hominin whose existence is known from a finger bone and two teeth found in a Siberian cave. No one knows what the Denisovans looked like, since we have no other fossils at our disposal. However, geneticists managed to decipher their genome with high accuracy.
David Reich from Harvard Medical School (USA) thoroughly examined the Denisovian genome and came to the conclusion that some segments do not fit into the big picture.
The genome suggests that the Denisovans were cousins of the Neanderthals - but this has long been known. Their line split from ours about 400 thousand years ago, before splitting into Neanderthals and Denisovans.
This should mean that Denisovans and Neanderthals are equally different from modern humans, but upon closer inspection, Mr. Reich discovered that this is not the case. “Denisovans are apparently farther from modern humans than Neanderthals,” the scientist says. For example, the scattered fragments, which account for up to 1% of the Denisovian genome, appear to be more ancient than the rest.
This is best explained by the fact that the Denisovans interbred with some other species. Or something happened that Mr. Reich himself says: "The Denisovites have preserved the hereditary information of an unknown archaic population that has nothing to do with the Neanderthals."
Johannes Krause from the University of Tübingen (FRG) considers the data presented to be convincing, "they are difficult to ignore." Mr. Krause is one of those geneticists who study the Denisovian genome in search of traces of interbreeding. The fact is that the teeth of the Denisovites are unusually large, as if we are facing a more primitive view. If the Denisovans did indeed interbreed with the archaic species, this may explain everything.
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So, what kind of people were they with whom the Denisovites became related? Mr. Krause is betting on a species already familiar to us, because many hominins are known only from fossils and have never been genetically analyzed. And many of them could meet Denisovites on their way.
The most likely candidate is a Heidelberg man, believes Chris Stringer of the Natural History Museum in London (UK). This species existed 250-600 thousand years ago. It originated in Africa, but then settled in Europe and western Asia. The early Denisovans, whose ancestors followed the same path, could get in touch with them.
Another option is Homo erectus. He was even more widespread than Heidelberg man: he even reached Java. But its western populations - occupying the same territory as the Denisovans - could not wait for them.
DNA analysis of a Heidelberg man could clarify the situation, but this is easier said than done. The genome of Denisovans and Neanderthals survived primarily because they lived in cold and dry places. Other hominins preferred hot and humid areas where DNA decays quickly. A number of fossils have been found in Asia, the species of which cannot be established, and scientists are so far unsuccessfully struggling to isolate DNA samples from them.
Whoever that mysterious people turned out to be, the main thing is to understand that interspecific crossing was completely commonplace in the history of human evolution. After our direct predecessors left Africa, they "slept" with both Neanderthals and Denisovans. And while the ancestors of today's African hunter-gatherers never left the continent, recent research has shown they weren't squeamish about unidentified hominins. Apparently, this episode took place about 35 thousand years ago, and they were interested in representatives of a species that separated from our line about 700 thousand years ago.
The results of the study were presented in London at a discussion meeting of the Royal Society on ancient DNA.