Denisovan's largest fossil still reveals old human secrets

Scientists have unearthed the most complete remains of the mysterious group of ancient hominins known as Denisovans. The jaw, discovered high on the Tibetan Plateau and dated over 160,000 years ago, is also the first specimen of Denisovan discovered outside the Siberian cave in which the hominin was found there is a ten years – confirming the suspicions that Denisovans were more widespread than the fossil record. currently suggests.

The research marks the first time that an ancient human being has been identified solely by protein analysis. In the absence of usable DNA, scientists have examined the proteins present in the teeth of the sample, leaving hope that more fossils could be identified even when DNA does not occur. is not preserved.

"It's a fantastic job," says Katerina Douka, an archaeologist at the Max Planck Institute for the Science of Human History in Jena, Germany, who is leading a separate project to discover Denisovan's fossils in Asia. "It tells us that we are looking for the right sector."

Denisovans hunt

Until now, all that scientists have learned about Denisovans comes from a handful of teeth and bone fragments from the cave of Denisova, in the Altai mountains, in Russia. The DNA of these remains revealed that the Denisovans were a sister group of Neanderthals, both descendants of a population that had separated from modern humans there are about 550,000 to 765,000 years old. And at Denisova Cave, both groups seem to be met and united: a bone fragment described last year belonged to an ancient-human hybrid individual who had a father Denisovan and a Neanderthal mother.

But many expected it was only a matter of time before researchers found traces of Denisovans elsewhere. Some modern humans in Asia and Oceania carry traces of Denisovan's DNA, suggesting that the hominin would have lived away from Siberia. And some researchers believe that China's ungraded fossils of humankind could be Denisovan.

The last specimen, described in Nature¹consists of one half of the lower jaw, with two complete teeth. A monk found him in the Baishiya Karst Cave in China in 1980 and passed him to Lanzhou University. But it is not until the 2010s that archaeologist Dongju Zhang and his colleagues began to study the bone.

The team has encountered a problem. The remains of Denisova's cave had all been identified as they still contained DNA, which can be compared to the genetic sequences of other ancient humans. But there was no more DNA in the maxillary bone.

Instead, scientists have looked for old proteins, which tend to last longer than DNA. In dentin teeth, they found collagen proteins suitable for analysis. The team compared these with equivalent proteins in groups including Denisovans and Neanderthals, and found that they aligned most closely with Denisovans sequences.

The team was also able to gather other excerpts of information about the individual. One of the teeth was still erupting, for example, causing the authors to assume that the jaw belonged to a teenager.

Previous search² Chris Stringer, a paleoanthropologist at the Natural History Museum in London, explains Chris Stringer, paleoanthropologist at the Natural History Museum, who has identified Neanderthals that use both protein and DNA. The method could prove particularly useful for older samples or those from Southeast Asia and other hot climates, where DNA is degraded most rapidly.

But the field is still in its infancy, says Stringer, and the analysis of ancient proteins currently contains a smaller sample of early hominins for comparison than the DNA analysis. "While this certainly suggests a connection to the Denisovans, I think I would like to see larger samples to really clarify more," he says.

Douka agrees: for now, the analysis of ancient DNA remains the "gold standard" for this type of work, she says. Although there is no genetic material in the jawbone, Douka wonders if researchers could still find DNA in the Tibetan cave, perhaps even in sediments.

The roof of the world

The elevation of Denisovan's new house, 3,280 meters above sea level, surprised researchers and resolved a mystery about the genetic contribution of Denisovans to modern Tibetans. "It's amazing that all the ancient humans were at this altitude," says Stringer.

Some Tibetans have a variant of a gene called EPAS1 this reduces the amount of hemoglobin, a protein carrying oxygen, in the blood, allowing them to live at high altitude with a low oxygen level. Researchers³ thought that this adaptation came from Denisovans, but it was difficult to reconcile with the relatively low altitude of the cave of Denisova, 700 meters. The latest study suggests that Denisovans have developed adaptation on the Tibetan plateau and have moved on to Homo sapiens Frido Welker, molecular anthropologist at the University of Copenhagen, says his co-author, when the species arrived about 30,000 to 40,000 years ago. If Denisovans in Asia were adapted to high altitudes, similar sites could host more of their remains.

He points to the Sel'Ungur cave in Kyrgyzstan, located at about 2,000 meters above sea level, where an arm bone of a hominid child was found but did not reveal any DNA. "Now I'm wondering, maybe this specimen is also a Denisovan and not a Neanderthal, as we usually assume," says Bence Viola, a paleoanthropologist at the University of Toronto in Canada.

Reassess fossils

And the fossil will probably encourage scientists to reconsider the classification of other remains. "We can cope with the fossil record and connect more and more specimens with the Denisovans," says Viola.

One candidate is a jaw bone called Penghu 1, which was caught in a fishing net near Taiwan and has many similarities to the last mandible. Welker and his colleagues hypothesized that this jaw could be Denisovan – but the ultimate proof will come from the analysis of DNA or proteins, says Welker.

Sampling of protein or DNA remains is inherently destructive, so it must be justified, he adds. "It's not a light decision to make."