Ancient Siberian Ghost Tribe Reveals Secrets

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Ancient Siberian Ghost Tribe Reveals Secrets
Ancient Siberian Ghost Tribe Reveals Secrets
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A mysterious group of extinct humans known as the Denisovans are changing our understanding of human evolution. Who are they? Years have passed since the discovery in Denisova Cave in southern Siberia, and scientists hope to find new remains of this ancient population.

Samantha Brown had little hope when she opened the zipper on the bag, which contained about 700 bone fragments. She was warned that it would take a lot of work to analyze these bones, and that they were unlikely to belong to a person.

These were the remains from Denisova Cave in southern Siberia, where archaeological excavations were carried out, and where scientists in 2010 discovered a previously unknown group of ancient people. Researchers named them Denisovans and identified the remains by the DNA preserved in the finger bones. Thanks to this find, the distant Siberian cave has become one of the most important archaeological sites in the world.

Brown went through the entire bag of bones, checking each for homo sapiens. She found bears, bison, hyenas, and even mammoths with rhinos. But there was not even a trace of a man. Therefore, she went to Siberia to collect more samples found in Denisova Cave, realizing that she had very little chance.

Luck smiled at Brown in June 2015, when traces of human collagen were found in a 2-centimeter long bone fragment. “It was an incredible moment when we found out that one of the fragments is human,” she says. But she was completely unprepared for the subsequent discovery of her colleagues from Germany. German scientists have sequenced the complete DNA genome in the bone. Last year, the team, which included Brown, reported that the bone belonged to a girl who lived about 100,000 years ago. Her mother was Neanderthal and her father Denisovan. Scientists gave this unusual girl the name Denny.

“First of all, it was one chance in a million, and we did not miss it. Secondly, it was the offspring of the first generation. It's magic, it's amazing, says Brown. "It shows how much we can discover."

After that, Brown and her colleagues found other fragments of hominin bones in Denisova Cave. The team is now beginning to analyze tens of thousands of bone fragments from this cave and elsewhere in Asia. There are other projects, the common goal of which is to search for Denisovans throughout the continent, where traces of their DNA are found in many modern people. Scientists hope to determine the zone of distribution of this mysterious group, which could have dispersed across Siberia and reach Oceania, as well as trace their contacts with other representatives of the human race, including Homo sapiens and Neanderthals. Many scientists dream of finding more complete remains of the Denisovans and artifacts in order to find out what they looked like and how they could behave.

Almost 10 years have passed since the opening of the Denisovites, and now they are beginning to acquire clearer outlines, attracting increased attention. Scientists are confident that they will soon find new remains of this ancient population, and outside the Denisova Cave (if they have not already found it). Researchers started talking about the fact that some of the unusual fossils in China may have belonged to the Denisovans.

“The real hunt for Denisov's man has begun,” says archaeologist Andrei Krivoshapkin, who works in Novosibirsk at the Institute of Archeology and Ethnography of the Siberian Branch of the Russian Academy of Sciences.He participates in the excavation of caves near Denisovaya and other places in Central Asia in search of answers to questions.

Hermit cave

Denisova Cave is located at the foot of the Altai Mountains near the Russian border with Mongolia, China and Kazakhstan. It is located in a picturesque river valley, reminiscent of Switzerland to some visitors. According to legend, the cave got its name from a local shepherd or hermit of the 18th century, who took refuge in its high-vaulted halls. The cave is located in a hard-to-reach place, even for explorers who flock there during the six-month excavation season in the spring and summer. “You are completely cut off from the world there,” says Katerina Douka, an archaeologist and curator Brown who works at the Max Planck Institute for the Study of Human History in Jena and first visited the cave in 2013. "This is a real paradise."

Soviet archaeologists began excavating the cave in the late 1970s and early 1980s, discovering tens of thousands of stone tools and animal bone fragments, many of which were devoured and digested by hyenas and other predators living in the cave. In 2009, Svante Pääbo, a geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, obtained a small and broken bone from a hominin's toe that Russian archaeologists had found in a cave a year earlier. He thought that it could have belonged to a Neanderthal, since his researchers found DNA from this group in fragments of the remains from a nearby cave. However, Paabo did not pin much hopes on his find, because the bone was very small and could hardly contain a large amount of DNA. "It took about six months," he says, "before we started studying it."

This fragment is called Denisova 3. It raised questions to which scientists have not yet found comprehensive answers. The DNA found in it indicates the existence of a mysterious new hominin and suggests that the Denisovans and Neanderthals descended from an ancient population, which, as further studies showed, moved away from modern humans about 800 thousand years ago and could live throughout Asia. The inhabitants of the continent still, in one proportion or another, carry the heritage of the Denisovan man.

Denisova Cave remains the only place where Denisovites have been found. The discovery of Denny's remains indicates that different groups of people once settled in this place. If we are talking about clarifying contacts between such groups, Paabo notes, then this is one of the most important, if not the most important place in the world.

After the discovery of the Denisovan man, scientists used DNA sequencing to identify several molars found in the same cave and eventually assigned them to the same group. They also found other remains with Neanderthal DNA. Denny's DNA analysis has revealed some very important details about these groups. “We knew that Denisovans and Neanderthals were there. But we didn’t think they had such close contact,”says Paabo. "It's amazing to find direct evidence, to find these people practically in the process of mixing."

Denny's discovery convinced Paabo and other scientists that they would find even more of the same remains of two groups of hominins - maybe even in Denisova Cave. Researchers who analyzed Denny's genome found signs that her father, who was clearly Denisovan, also had hereditary traits of Neanderthals in the chromosome set of her father, indicating earlier contacts between the two groups. “We have to find these people,” says Duka.

“There is still a lot of mystery here,” adds Oxford University archaeologist Tom Higham, who works with Dooka and Brown. "It was either incredible luck, or interspecies crossbreeding happened so often that we can count on other finds of this kind."

Crossroads

Some researchers hope to stumble upon another Denny, while others are trying to determine the periods when different groups of homo sapiens crossed or even interbred in Denisova Cave. Geochronologists Zenobia Jacobs and Richard Roberts, based at the University of Wollongong, Australia, have led a team of researchers to determine the age of sedimentary deposits in Denisova Cave by analyzing hundreds of thousands of grains of quartz and feldspar.

Judging by the oldest stone tools found there, the first inhabitants of the cave settled there about 300,000 years ago. Presumably they were Denisovans or Neanderthals. The Denisovans occupied it 55-200 thousand years ago, as evidenced by the layers in which the Denisova 3 fragment was found. The Jacobs and Roberts group also determined from the sediments and remains of the Neanderthals that these human ancestors lived in the cave 100-190 thousand years ago.

This means they have overlapped for a long time, but Jacobs cautions that her team cannot yet accurately determine these periods due to a lack of samples. Paabo's team is studying hundreds of sediment samples in search of hominin DNA, hoping to better determine when Denisovans and Neanderthals lived in the cave, and whether they intersected.

Denisova cave

There are also some clues indicating that the cave was inhabited by a modern man who may have met these groups. In earlier layers, archaeologists discovered tools and ornaments made of bones and teeth of deer and other animals that resemble artifacts found on the first Homo sapiens who penetrated Europe in the early Upper Paleolithic period, which began about 50 thousand years ago. A group of scientists led by Dooka and Higham calculated that these artifacts are from 43 to 49 thousand years old. But in the bone fragment, which is 46-50 thousand years old, there is no DNA that allows to establish the belonging of its owner to this or that group.

The leading excavations in the cave, Russian archaeologists suggested that the found tools and decorations were made by the Denisovites, and that this group possessed the ability of symbolic thinking. However, Western archaeologists prefer the theory that these artifacts were made by early modern people, whose remains are found in another Siberian town of Ust-Ishim, and attribute them to the early Upper Paleolithic.

Now scientists are searching for the earlier layers of Denisova Cave, hoping to find more remains and DNA there that will help to find out who made these artifacts. Similar work is underway in other archaeological sites in Siberia, including near the Denisova Cave. She, too, can provide answers to questions. “A lot of interesting things are happening, and they are happening fast,” says Higham.

Looking for bones

Scientists are constrained by the lack of organic remains of the Denisovites. Bence Viola has studied a lot, including Denisova 3, as well as several unusually large molars that are unlike those of Neanderthals and modern humans. “All the Denisovans' material fits in a very small box,” says Viola, a paleoanthropologist at the University of Toronto, Canada. - I looked at these tiny fragments and teeth for a very long time. I’m probably the only one who saw them all.”

But gradually more and more new material appears. Archaeologists conducting excavations in Denisova Cave, in 2016, found a fragment of the parietal bone that is part of the skull, which contains the mitochondrial DNA of the Denisovan man. The shape of this bone is almost the same as that of Homo erectus, or Homo erectus. Most scientists believe that this species is a close ancestor of humans, Neanderthal and presumably Denisovans. “Unfortunately, it’s not very informative, I expected more,” says Viola, who will talk about his research in March at the annual conference of the American Association of Physical Anthropologists.He hopes that he will soon be able to find other fragments of the parietal bone or even the entire skull. “It would be nice to get something more,” says Viola.

There is no shortage of fragmentary remains. This month, Higham tweeted a photo of a long bone fragment in a small plastic bag. “Good luck, little Denisov's bone,” he wrote, although he does not yet know which group it belongs to. If you count the fragment of Denny's finger, then this is the fifth bone from the cave, identified as human. The scientist uses a method called Zooarcheology by Mass Spectrometric Analysis (ZooMS). It was designed to quickly identify the bones of animals, of which there are often a great many in the excavation sites. Using this method, researchers break down collagen, which is most in the bones, into smaller peptides, and then use a mass spectrometer to determine the differences between animal species. Hominins have identical peptide sequences, so DNA is needed to assign the remains to a specific group.

Having achieved the first successes in their work, Duca and colleagues received in 2017 from the European Research Council two million euros in funding for an expanded search for the Denisovan man in 20 locations in Europe and Asia. In total, they have to sort out 30-40 thousand bones. “There are days that are very encouraging, and sometimes you go through a thousand bones and find a thousand hyenas,” says Duka. "I have a feeling that the search should be carried out in China."

An employee of the Institute of Archeology and Ethnography of the Siberian Branch of the Russian Academy of Sciences is engaged in cataloging finds found during excavations in Denisova Cave

Other scientists share Duca's insights, mainly due to the distribution of Denisovan DNA among modern humans. It is often found among the Chinese. Some scientists suspect that the skeleton of a Denisovan is already beating its thumbs in some museum collection in China. For example, in 2017, paleoanthropologists described the unusually large skulls of hominins that lived 105-125 thousand years ago. They were found during excavations in central China near the city of Xuchang. Based on their age, location and anatomical features, some scientists have suggested that these are the skulls of the Denisovans. “Where could Denisovans live outside Denisova Cave?” Asks Chris Stringer, a paleoanthropologist at London's Museum of Natural History. "They were supposed to live there in China."

Viola says that the skulls from Xuchang do not in any way resemble his parietal bone fragment. He is more interested in the remains from northern China, found in the town of Xujiao, which are about 300 thousand years old. Among them are molars, similar to the finds from Denisova cave. “I would be very surprised if it turns out that the Chinese material, especially from Xujiao, is not Denisovans,” he says.

Geneticist Qiaomei Fu, who created a research laboratory for ancient DNA at the Beijing Institute of Paleontology and Paleoanthropology of Vertebrates at the Chinese Academy of Sciences, together with his team analyzed skulls from Xuchang and other fragments that could belong to Denisovans. He says with regret that homo sapiens DNA has not yet been found in these remains.

Perhaps proteinaceous substances will give scientists a better chance of finding a Denisovan man in China or elsewhere in Asia, because they usually last longer than DNA. Duka has just recruited a Chinese graduate student to analyze samples and hopes to be able to analyze remains from Southeast Asia and Papua New Guinea.

Since the shape of collagen studied by the ZooMS method does not differ in Denisovans and in other hominids, scientists will have to sequenced bone proteins, which have more variability, in order to find Denisovans.Molecular anthropologist Frido Welker of the Natural History Museum of Denmark has just embarked on a project to find out if the remains contain a hominin, including potential Denisovans from the Early and Middle Pleistocene (this period began 2.6 million years ago, and ended 126 thousand years ago), proteins indicating evolutionary relationships. “This is a period of time when ancient DNA is not always preserved, but proteins survive,” says Welker.

Many scientists suggest that the Denisov Cave became the northern outpost of the Denisovans and other hominins when the climate allowed them. But although ancient populations disappeared from these places many millennia ago, the cave still attracts different groups of scientists like a magnet. In July 2018, anthropologists, archaeologists and geneticists, obsessed with this cave, gathered there to share their discoveries and findings. The conference was called "The Beginning of the Upper Paleolithic in Eurasia and the Evolution of the Human Race", but it could well be called "Denisomania".

This was Brown's first trip, and she knew she would be amazed by this cave that had given the world so many discoveries. She says that the surrounding landscape, lush vegetation and local beauty told her why Denny and her relatives were so attracted to these places. "You can imagine that people just wanted to be here."

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