Ancient skull, a new window on human migration, Denisovan conference

Ancient skull, a new window on human migration, Denisovan conference
Enlarge / This excavation confirmed Denisovan DNA within the sediment.

Dongju Jang, Dongju Jang, Lanzhou University

Denisovans occupy a very strange place in human history. Like the Neanderthals, they are the earliest points of production of modern man and later departure from the lineage mixed with modern man. However, we’ve known about Neanderthals for about 150 years, but we got their DNA sequences and identified a set of anatomical features that define them. In contrast, we had no idea that Denisovans’ DNA existed until unexpectedly found on one little finger piece. And to this day, we haven’t identified enough ashes to really say about what they look like.

However, over time we have been increasing our sample of ancient DNA that provides a clear picture of our interactions with this enigmatic lineage. Now, two new reports describe ancient DNA that provides more detailed information. One paper describes the modern human genome in Asia that is nearing a time when crossbreeding should occur. This provides additional evidence that there have been at least two cases of interbreeding and helps clarify how the early population moved in Asia. The second confirms that Denisovans lived along the Tibetan plateau and may have adapted to high altitudes.

Mongolian skull

In 2006, mining in Mongolia’s Salkhit Valley clearly revealed the top of an old skull. However, since there was no decisive feature, people would say whether it is Neanderthal or Standing man. However, preliminary DNA sequencing has been shown to be from modern humans, dating to approximately 34,000 years by carbon dating.

It’s actually a major period in human history. At this time, East Asians and East Eurasians (or Siberians) were distinct, and the latter were somewhat related to West Eurasians. Their history is incredibly complex. The 40,000-year-old skeleton from near Beijing is clearly closest to modern East Asians, but most closely related to the skeletons (!?!?) found in Belgium. It seems that the 45,000-year-old Siberian skeleton has no modern relatives, and 24,000-year-old individuals from the same region have identified a population mixed with East Asians for production. Native American ancestors. However, two other Siberian skeletons of approximately the same period do not exhibit such affinity and generally look Eurasian.

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

Given that confusion, additional DNA from those times and regions may be useful. So researchers did what became the standard procedure for dealing with such old DNA. They first looked for sequences that matched human DNA to extract all human-like sequences. To decontaminate modern people, they searched for the most common signs of damage that occurs as DNA ages. Obviously human and the damaged one was used to create the genome.

The end result is what was expected given the age at the top of the skull. Most of the mutations in DNA matched those of modern people, but there were many regions that matched Neanderthals and Denisovans. The part of modern man is the closest match to the East Eurasian and Native American population, confirming previous results.

Too much breeding

But it’s still almost as confusing as before. “that much [newly described] Salkhit individuals share many alleles with Tianyuan. [Beijing] The researchers wrote, “as individual as an instance of Jana from northeastern Siberia, ~ 31,000 years old.” “However, Tianyuan and Yana individuals share fewer alleles than Salkhit individuals.” The Western and Eastern Eurasian populations were separated, resulting in some crossbreeding between Eastern Eurasians and East Asians.

But, of course, the newly described Siberian DNA has striking similarities to the Belgian skeleton, suggesting that at least some Western Eurasian DNA is still returning to lineage.

Other ancients

As far as Neanderthals go, the new Siberian skeleton is typical of the modern Asian population, with about 1.7% of its DNA coming from Neanderthals. Denisovan’s content is more difficult to judge, but researchers have found 18 large DNAs inherited from Denisovan. Because of this size, researchers have concluded that crossbreeding took place about 10,000 years ago. That is consistent with the complete absence of Denisovan DNA in the 45,000-year-old Siberian skeleton. And the Denisovan DNA present is more consistent with the amount seen in the later East Asian skeleton.

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What is interesting here is that the segments present in the new Salkhit genome do not overlap with those found in modern human genomes in Southeast Asia and the Pacific region. The obvious conclusion from this is that modern humans mingled with Denisovans in at least two separate cases. That’s pointed out in other findings, but modern East Asians have the DNA of these two events. The Salkhit genome provides a clear separation between them.

Meanwhile, there is a separate treatise on the place where the Denisovans live, especially the Baisyya karst caves on the edge of the Tibetan Plateau. Well over 3,000 meters (nearly 11,000 feet) above sea level, it was a very high altitude environment and would have been difficult to make home during the last Ice Age. However, part of the jawbone was found there. No DNA was produced, but the protein fragment indicates that the jaw it came from belongs to Denisovan.

DNA from dirt

Most ancient DNA samples have been heavily contaminated by bacteria with heavily damaged and fragmented DNA. As a result, researchers have developed various procedures to help isolate human-like DNA and recognize ancient DNA based on accumulated damage patterns. Gradually, I realized that these same techniques could work even when contamination is higher and human sequences are much more rare: soil samples. So we couldn’t get DNA from the jawbone, but one team decided that DNA could remain in the environment it originated from.

So, the team dug up sediments at the bottom of the cave and dated the different layers to create an estimated chronology. Most of the layers have mammalian DNA that is quite old depending on the damage. So the researchers took out human mitochondrial DNA and began to sequence them. It was obviously Denisovan, and there were some possibilities for a small part of modern human DNA.

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Overall, there are signs that Denisovan lived from 100,000 to about 30,000 years ago. It’s a broad history of occupation, but we don’t know if it is constant, seasonal, or sporadic. Nevertheless, 70,000 years are certainly enough time to acclimate to high altitudes, researchers point out. And it turned out to be consistent with another genetic discovery. Some of the Tibetan genetic adaptations are at high altitudes. Inherited from Denisovans.

Science, 2020.DOI: 10.1126 / science.abc1166, 10.1126 / science.abb6320 (DOI information).

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