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A New Window on Ancient Skull Human Migration and Denisovan Meetings

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Zoom in / Through this excavation, Denisovan DNA was found inside the remains.

Dongju Shang, Dongju Shang, Lanzhou University

The Denisovans have a very strange place in the history of mankind. Like the Neanderthals, they are the earliest branch of the race that produced modern humans and later interacted with modern humans. We got to know the DNA sequences of Neanderthals about 150 years ago and identified a set of anatomical features that define them. On the other hand, we did not know that the Denisovans existed until their DNA unexpectedly appeared on a single little finger. Also, to date, we have not identified enough debris to say anything about what they look like.

But over time, the number of ancient DNA samples has increased, giving us a clearer picture of our interactions with this enigmatic species. Now, two new reports describe ancient DNA in more detail. An essay describes a modern human genome from Asia, which is approaching the time when breeding should take place. This provides further evidence that there are at least two breeds, and helps to illustrate how the early human population in Asia moved. The second confirms that the Denisovans inhabited the Tibetan plateau and may have adapted to higher altitudes.

Mongolian skull

In 2006, excavations in the Salkit Valley of Mongolia uncovered an old skull. But since it has no specific features, people have argued that it may or may not be Neanderthal The man standing. However, primary DNA sequencing indicated that it belonged to a modern human, and that carbon dating is about 34,000 years old.

It was, in fact, the turning point in the history of mankind. At this time, the East Asian and East Eurasian (or Siberian) populations were different, the latter being related to Western Eurasians. Their histories are extraordinarily complex. The 40,000-year-old skeleton near Beijing is very close to modern East Asia, but it is closely related to a skeleton found in Belgium (! ??!?). The 45,000-year-old Siberian skeleton does not appear to have modern relatives, while a 24,000-year-old man from the same area has been found to produce population in conjunction with East Asians. Ancestors of Native Americans. The other two Siberian skeletons from about the same period do not show that connection, and are generally found to be Eurasian.

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If you are not confused after that, go back and read it again.

Given that disorder, more DNA from that period and region would be useful. Therefore, the researchers did become a standard procedure for dealing with this old DNA. They first searched for sequences that matched human DNA to extract all human-like sequences. To eliminate pollution from modern humans, they searched for the most common signs of destruction that have occurred over the ages of DNA. Apparently anything human and damaged was used to put a genome together.

The end result was about what you would expect considering the age of the skull top. Most variations in DNA are compatible with modern humans, but there are several regions that are compatible with Neanderthals and Denisovan. Modern human parts are most compatible with East Eurasian and Native American populations, which confirms previous results.

Too much breeding

But it is still as confusing as before. “The [newly described] Salkit shares several alleles with the individual Tianyuan [Beijing] Researchers also write that individuals are similar to 31,000-year-old Yana individuals from northeastern Siberia, yet Tianyuan and Yana individuals share a few alleles with each other other than the Salkit person. ”Overall, the researchers concluded that after some time the western and eastern Eurasian populations split, and there was some breeding between East Eurasians and East Asians.

Indeed, the newly described Siberian DNA bears a striking resemblance to the skeleton from Belgium, indicating that at least some Western Eurasian DNA is still being reproduced.

Other ancestors

As for Neanderthals, the new Siberian skeleton is very common in the modern Asian population, with 1.7 percent of its DNA derived from Neanderthals. The contents of Denisovan are difficult to break down, but researchers have found 18 large DNA genes inherited from Denisovan. Their size suggests that interbreeding took place about 10,000 years ago. This corresponds to the complete absence of Denisovan DNA in a 45,000-year-old Siberian skeleton. The current Denisovan DNA is more compatible with the size found in later East Asian skeletons.

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The interesting thing here is that the segments in the new Salkit genome do not overlap with the segments found in the genomes of modern peoples in Southeast Asia and the Pacific. The obvious conclusion from this is that modern humans interact with Denisovans at least on two different occasions. That is one of the other results mentioned, but modern East Asians have DNA from these two events. The Salkit genome makes a clear distinction between them.

Meanwhile, a separate essay looks at where the Denisovans live – especially in the Baishia Karst cave on the edge of the Tibetan Plateau. At an altitude of more than 3,000 meters (approximately 11,000 feet) above sea level, it had a very high altitude, making it difficult to build a house during the last ice age. Yet a part of the jawbone was found there. Although it does not provide any DNA, the protein fragments indicate that the jawbone belongs to a Denisov.

DNA from dirt

Most ancient DNA samples are highly contaminated with bacteria, poorly decomposed and decomposed DNA. As a result, researchers have developed various procedures to isolate human-like DNA and to identify ancient DNA. Gradually, it was realized that the same technologies would work where pollution is high and the human range is more rare: soil samples. So, when we were unable to extract DNA from the jawbone, a team decided that some of the environment in which it came from was left.

So, the team dug through the debris on the floor of the cave and dated different layers to create an estimated chronology. Most of the layers contained mammalian DNA, which is very old in terms of damage. Therefore, researchers began extracting human mitochondrial DNA and regulating it. Denisovan contained only a small fraction of modern human DNA.

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In total, Denisovan has traces from 100,000 years ago to 30,000 years ago. Although we do not know whether it was permanent, chronological, or rare, it is extensive history. Regardless, researchers point out that 70,000 years is indeed enough time. It turns out to be compatible with another genetic discovery: some genetics of Tibetan to high altitude Inherited from Denisovan.

Science, 2020. DNI: 10.1126 / Science.Absi1166, 10.1126 / Science.ab6320 (About DOIs).

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