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In a new study, an international team of scientists analyzed DNA from more than 700 sediment samples collected from the Pleistocene layers of the Denisova Cave in Siberia, and found ancient mitochondrial DNA (mtDNA) of hominins and mammals in 685 samples and 175 samples, respectively.

The earliest evidence of hominin mtDNA is from Denisovans and is associated with stone tools that were deposited approximately 250,000 to 170,000 years ago; Neanderthal mtDNA first appears towards the end of this period.

The scientists also found a turnover in the mtDNA of Denisovans, which coincides with changes in the composition of the mtDNA of the fauna, and evidence that Denisovans and Neanderthals repeatedly inhabited this place-perhaps before or after the beginning of the initial Upper Paleolithic, at least 45,000 years ago, when modern human mtDNA was first discovered in sediments.

Denisova Cave in the Altai is a typical habitat of Denisovans, an archaic group of hominins related to Neanderthals.

The cave consists of three chambers (designated as the Main, Eastern and Southern), which contain deposits from the Middle Pleistocene to the Holocene epoch.

The dozen hominin remains recovered from the sediments also include Neanderthals and children of Neanderthals and Denisovans, suggesting that the cave was a contact zone between these archaic hominins.

However, there is uncertainty about the order in which these groups appeared on the site, the time and ecological context of the presence of hominins, as well as the connection of certain hominin groups with archaeological finds.

"It took us a long time to simply collect hundreds of samples from all three chambers in the cave and document their exact location, but we have obtained an exhaustive set of samples covering more than 300,000 years of Siberian history," said Professor Zenobia Jacobs, a researcher at the University of Wollongong.

"The chronology created earlier for cave deposits allowed us to choose the best places to collect DNA samples and get the most out of the unusual DNA findings of the deposits."

In the new study, scientists extracted and sequenced small traces of mtDNA of ancient people and animals (such as cave bears, hyenas and wolves) from 728 samples of bottom sediments.

By matching the DNA profiles with the age of the layers, the researchers found that the first people to visit the site were Denisovans about 250,000 years ago, followed by Neanderthals about 200,000 years ago.

At the same time, only Neanderthal DNA was found in sediments whose age is between 130,000 and 80,000 years ago.

The Denisovans who returned after this time carried a different mtDNA compared to the Denisovans who were there earlier, which suggests that a different population arrived in the region.

The ancient DNA of anatomically modern Homo sapiens is first discovered in layers deposited approximately between 60,000 and 45,000 years ago and containing pendants and other ornaments made from animal bones and teeth, mammoth tusk, ostrich eggshell, marble and precious stones.

"This is not only the first evidence of the presence of modern humans in this place, but also suggests that they may have brought new technologies with them to the region," the researchers say.

The scientists also found animal DNA in almost all the samples and identified two time periods when changes occurred in both animal and human populations.

The first, about 190,000 years ago, coincided with the transition from relatively warm to relatively cold conditions, when the populations of hyenas and bears changed and Neanderthals first appeared in the cave.

The second major change occurred between 130,000 and 100,000 years ago, along with a change in climate from relatively cold to relatively warm conditions.

During this period, the animal populations changed again, the Denisovans disappeared, and the Neanderthals remained the only inhabitants of the cave.

The coincidence of these population movements with the climatic transitions between the interglacial and ice ages suggests that environmental factors played a key role in shaping the history of people and fauna in this region.

"Being able to get such dense genetic data from archaeological excavations is like a dream come true," said Professor Matthias Meyer, a researcher at the Max Planck Institute for Evolutionary Anthropology.

"There is so much information hidden in the sediments – it will keep us and many other geneticists busy all our lives."

An article about the study was published in the journal Nature.

Photo-Denisova cave-located in the Soloneshensky district of the Altai Territory. The cave area is 270 square meters, the length is 110 meters. Among the indigenous population, the cave is called Ayu-Tash (Bear Stone).

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