Monday , March 1 2021

Neanderthals and Denisovans have divided a Siberian cave for thousands of years, new research suggests.



Denisova cave in southern Siberia has been home to Neanderthals and Denisovans for thousands of years, but the issues remain about the timing of your stay. A couple of new studies traced the history of archaic human occupation on the scene, showing who lived there and when – including a possible time when the two now extinct species would go out together.

Two papers published today in Nature present an updated schedule for the occupation of the Denisova cave by Neanderthals and Denisovans. The new research suggests that the Denisovans – a sister species to the Neanderthals – made this cave their home for a longer period than the Neanderthals, first venturing into the cave 287,000 years ago. Neanderthals arrived at the site about 140,000 years ago, possibly sharing space with the Denisovans for thousands of years. It is further evidence that the Neanderthals and the Denisovans mingled – and that this co-mingling happened in or near Denisova.

Archaeologists and paleontologists have carefully scoured Denisova's cave for the past 40 years, removing several bones from animals and Neanderthals. But the real bomb came in 2010 with the discovery of a finger bone of previously unknown human species, the so-called Denisovans. Genetic analysis suggests that the Denisovans were a species related to Neanderthals, but virtually everything else about them remains a mystery, such as when they first appeared on the scene and when they died.

The Denisova cave, located at the foot of the Altai mountains in southern Siberia, is therefore a critical resource for improving our understanding not only of Denisovans but also of Neanderthals. And possibly our own species Homo sapiens"Though the cave, perhaps strangely enough, has not produced a single fragment of evidence showing that anatomically modern humans have lived there. For Neanderthals and Denisovans, however, Denisova cave served as an important refuge for vast tracts of time.

Vast ranges of time, in fact. We are not talking about a thousand years here or a thousand years there. On the contrary, we are talking about hundreds of thousands of years of occupation. Compiling a timeline of events, such as when the cave was first occupied and by whom, proved to be difficult, in part due to the large size of the cave and its complex layers of sediment; the stratigraphy of the cave encompasses both the Middle Paleolithic period of Siberia (between 340,000 and 45,000 years ago) and the Early Upper Paleolithic period (approximately 45,000 to 40,000 years ago).

Scientists have also been faced with the limits of radiocarbon dating, which can last only 50,000 years. The cave was inhabited for much longer than that, requiring the use of less reliable dating methods and, consequently, the placement of unconvincing or controversial timelines.

To overcome these obstacles and limitations, a multidisciplinary team of researchers from around the world, including from Russia, the UK, Australia, Germany and Canada, has spent the past five years analyzing bones and artifacts found in Denisova Cave. The researchers used various dating techniques, well-established techniques and cutting-edge techniques, and statistical techniques to date thousands of items at the site, allowing them to put together the most accurate and detailed timeline up to the time of human occupation at Denisova Cave.

The first study, led by Zenobia Jacobs and Richard Roberts of the University of Wollongong in Australia, presented new dates for sediment deposits in Denisova caves. To date, such deposits and, consequently, bones and internal artifacts, researchers have used a relatively new technique called stimulated luminescence, in which scientists may say the last time a mineral grain, such as quartz, has been exposed to sunlight. Dates were provided for 103 sediment deposits covering 280,000 years of history in the cave.

The results of this work showed that Denisovans occupied the cave about 287,000 years ago, and continued to live in the cave until about 55,000 years ago. Neanderthals arrived in the cave about 193,000 years ago and continued to live there until about 97,000 years ago – a 96,000 year overlap. The bones of 27 animals, including mammals and fish, along with 72 species of plants were also analyzed, pointing to a variable climate in the region during the millennia of occupation in the cave. Sometimes the region was relatively warm, with broad-leaved tree forests, but at other times it was a harsh, desolate tundra-steppe habitat.

An important implication of the Jacobs and Roberts study is the suggestion that the Denisovans and the Neanderthals grouped together in the cave. Now it is possible that the two species did not share the space at the same time, but recent evidence suggests that they probably did. In a surprising finding last year, a group of scientists, some of whom co-wrote this new study, discovered genetic evidence of an archaic hybrid hominid, dubbed Denisova II, who lived in the cave 90,000 years ago – a girl with a Denisovan's father and a Neanderthal mother.

This evidence, along with other lines of research, suggests that the two species cross regularly and that this was not just an isolated case.

The second study, led by Katerina Douka of the Max Planck Institute for the Science of Human History in Germany, offered new dates for the Neanderthal and Denisovan fossils along with dental pendants and bony spots found on the site. Douka's team used various techniques to indirectly and directly date thousands of bone fragments and artifacts, including radiocarbon dating and uranium series dating, both taking advantage of known rates of radioactive decay.

"This is the first time we can confidently assign an age to the entire archaeological sequence of the cave and its contents," said Tom Higham, an archaeologist at Oxford University and co-author of the new study, in a statement.

Denisovan's oldest fossil suggests that this group was present at the site 195,000 years ago, while all Neanderthal fossils, including Denisova II, were dated between 80,000 and 140,000 years ago. The newest fossil of Denisovan was dated between 52,000 and 76,000 years ago.

"Douka's work is exciting because we knew that Neanderthals and Denisovans used the Denisova cave and that the two groups mingled there or nearby, but we did not know much about the time each group went to the cave or how long they lived. two groups overlap when using the cave, "said Sharon Browning, a research professor in the Department of Biostatistics at the University of Washington who did not participate in the new study at Gizmodo.

Many of the dates provided in the Douka newspaper had large margins of error, a consequence of complex stratigraphy (eg concerns that some items drifted to lower stratigraphic layers) and an unwillingness to go beyond the available data. But while there is "considerable uncertainty in some estimates, and the possibility of visits from any group that were sooner or later but did not leave a trace detected," Browning said that these results still "help establish the likely pattern of use Time . "

The artifacts found on the site, such as bony points, perforated teeth and pendants, date back 49,000 to 43,000 years and are now the oldest artifacts ever discovered in northern Eurasia, according to the Douka newspaper. The problem is that these dates are thousands of years after the last evidence of human occupation appears in the cave.

"Based on current archaeological evidence, one can assume that these artifacts are associated with the Denisovan population," the authors assume in the study. "It is not currently possible to determine whether anatomically modern humans were involved in their production, as modern human fossil and genetic evidence of such antiquity has yet to be identified in the Altai region."

The Denisovans were the likely makers of these items, because it is the simplest explanation, since Neanderthals had already disappeared from the cave and no evidence of modern humans exists in the cave, according to the new research. But anthropologist Chris Stringer of the UK's Natural History Museum is not convinced that these items belonged to the Denisovans.

"My money would be in the first modern humans, which can be mapped elsewhere on this date, for example, in Ust & # 39; -Ishim in Siberia, but the authors of Douka's article argue surprisingly that it is more parsimonious to assume that the Denisovans were responsible, even if no Denisovans are known as late as this, "Stringer said Gizmodo. "Just more discoveries and more research can solve this question satisfactorily."

Stringer said he liked the two new studies, saying they "bring the latest dating techniques to support stratigraphy, paleoclimatic records and human fossils," but he said many unresolved issues remain. There is the possibility, for example, that some, if not all, of the bones would be dragged into the cave by carnivores that hunted humans, or that the bones changed dramatically over the years of their original resting place, throwing away the courtship . considerably.

"But apparently it seems that Denisovans can be placed at least intermittently at the site for about 250,000 years, from almost 300,000 years ago to about 50,000 years ago, with Neanderthals also for intermediate periods," he said. Longarina. "The occupations seem to focus on warmer periods, reinforcing the view that the Denisova cave was probably at the northern edge of the occupation of both populations.

The fact that Neanderthals and Denisovans are present sometimes complicates much the dismemberment that humans were responsible for what elements of archeology – perhaps DNA sediment studies help map out their presence in the cave. "

These uncertainties and the large margins of errors are undeniably frustrating, but these two articles are helping to eliminate much of the ambiguity. Over time, we are gaining a clearer picture of the archaic human occupation in Denisova's cave. And damn, it's always fascinating.

[Nature, Nature]

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