Denisovan in the United States |  duty

Denisovan in the United States | duty

Ancient DNA reveals well-kept secrets about human migrations, evolution and interbreeding, but also about the history of pathogens and animals. The first article in a series on bubble paleobiology.

In January 2010, paleoanthropologist Bence Viola landed in Novosibirsk, Western Siberia, to better understand the origin of a mysterious bat. His Russian colleagues sent half of this fossilized bone, found in Denisova Cave, to the German laboratory he had just joined on a postdoctoral fellowship. Preliminary genetic analyzes indicated that this simple phalanx did not belong to a human like the others.

In the Siberian city, Russian archaeologist Anatoly Derevyanko pulled a “very huge” tooth from the same cave from his shirt pocket and showed it to fellow visiting Europeans. Mr. Viola, who is now a professor at the University of Toronto, was surprised. “When I saw this tooth, he says, I knew at once that it was not a modern man, not a Neanderthal: it was something quite different.”

A new human subspecies Discover : Denisovan. Comprehensive analyzes of the DNA of a 50,000-year-old phalanx will reveal it to be a close subspecies of Neanderthals that, without paleobiology, would likely remain in the shadows forever. And we will never know that our human race, sane manmixed with Denisovans and that many populations today bear the genetic marker.

ancient DNA

“When we started analyzing ancient DNA from fossils, people thought it was just a fad, and it couldn’t tell us anything new,” Viola says. History has proven these critics wrong: over the past twelve years, the number of scientific publications based on ancient DNA has grown exponentially. Prestigious magazines give them an offer like some other disciplines.

“The effectiveness of technologies has exploded over the past 20 years. This has opened many, many doors for us, bio-anthropologists and archaeologists, on specific questions we were asking ourselves about populations and individuals,” emphasizes Isabelle Ribot, a professor in the Department of Anthropology at the University of Montreal, who benefits From the analysis of ancient DNA to continue his research.

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A few large laboratories around the world drive the paleo ball. One of them is geneticist Svante Pääbo, of the Max Planck Institute for Evolutionary Anthropology, in Leipzig, with whom Pence Viola was working at the time of getting to know the Denisovan. Another ancient DNA professor who has had a tremendous influence in this field of research is geneticist David Reich of Harvard University.

Twelve years after the discovery of Denisovans, very few fossils are officially associated with these hominids, who may have had the build of soccer players. In Denisova Cave – also visited for thousands of years sane man And the neanderthal man – , Specialists attributed one phalanx, three teeth and a small part of the bone to the Denisovans. In 2019, fossil from another site – the mandible Xiahe, found in Tibet – was first associated with the Denisovan subspecies.

Thanks to these discoveries, a certain picture of the Denisovans was taking shape. “We thought it was a species adapted to cold regions and high altitudes, because it was found in the Himalayas and in the Altai. [en Sibérie] “,” notes French anthropologist Fabrice Demeter, professor at the GeoGenetics Center of the Lundbeck Foundation, University of Copenhagen. However, paleobiology soon casts doubt on this hypothesis.

Because once the genome of a Denisova man was decoded, researchers compared it to the genome of modern humans. They found only a small trace of the Denisovan genome among Europeans. However, they discovered up to 5% of Denisovan genetic material in certain groups from Southeast Asia and Oceania, such as Aetas in the Philippines, Papua New Guinea and indigenous peoples in Australia. Did Denisovans also live in the tropics, where they mixed with these populations?

Discover published this spring By a team that includes Mr. Demeter most likely answers this question.

Denisova in Laos

In 2018, Demeter and several colleagues were excavating the Tam Ba Ling Cave in Laos, where they had already found several ancient fossils. As usual, specialists excavated the surrounding area in the hope of discovering new archaeological sites.

Then the geologists and speleologists on the team found an entrance to a cave – “Cobra Cave” – ​​where fossil breccia, that is, a sedimentary rock containing fossils, is found. The teeth and bones, which once belonged to the humans and beasts living in the nearby plain, were moved here thousands of years ago due to torrential rains.

In such penetrations, all the bones are fragmented, but the teeth – the hardest part of the skeleton – are usually intact. One of the teeth found in a cobra cave aroused the researchers’ curiosity. By accurately comparing its shape with that of Denisova, they conclude that it belongs to this subspecies. “It was really a euphoric moment for the whole team,” says Mr. Demeter.

This summer, the team will analyze in the lab a few milligrams of dentin — the part of the tooth that’s under the enamel — from the sample to extract DNA. If this proves successful, then the membership of this fossil in the Denisovan group will be established without a doubt, although the authors of the publication are already convinced of this.

Thus, Denisovans now appear as organisms adapted to different climates. Many specialists believe that their territory, centered in China, was vast, and the fossils found so far are only on the sidelines.

Viola says the fossils found in China are already a “very good candidate” for Denisova. Western specialists are waiting for analysis from their Chinese colleagues to determine if Harbin’s skull – which belongs to an ancient human nicknamed “Dragon Man” – is a Denisovan. The lower jaw found by fishermen in the Taiwan Strait is also a fossil suspected to belong to a subspecies.

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Encounter with Homo erectus?

And what about the Denisova family tree? Paleogenomics tells us that Denisovans and Neanderthals diverged from our common ancestors about 500,000 years ago. Denisovans could have survived much later than their cousins: the hybridization observed today in Southeast Asia occurred between 50,000 and 20,000 years before our era, or even more recently. If these estimates are correct, then Denisovans will be the last surviving humans.

It is clear that mysteries remain about Denisova. A portion of its genome (4%) comes from an admixture with an older human population, whose identity is currently unknown. Professor Viola thinks it might be.Homo erectus, arrived in East Asia nearly two million years ago. This means that Denisova crossed his path – and shared his bed.

To see more clearly, it will be necessary to obtain more Denisovan DNA, but also to learn how to decode the genomes of ancient samples. This task is difficult: the passage of time breaks down the molecules that store genetic information.

There are also things that DNA can never tell us. What are the cultural customs of the Denisovans? What stone tools did they use? The discovery of a cave inhabited exclusively by this subspecies will help answer these questions. Like any genomics science will never kill archeology.

“It’s always interdisciplinary work,” says Isabelle Ribot. “You have to put everything in context, find interesting research questions. Otherwise, what’s the point of ancient DNA?”

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