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Home / Science / Ancient skulls are a new window for human migration, but Nisova Conference

Ancient skulls are a new window for human migration, but Nisova Conference



An image of a large, lit trench with people working on it.
enlarge / These excavations found Denisovan DNA in the sediment.

Dongju Zhang, Dongju Zhang, Lanzhou University

The Denisovans occupy a very strange place in human history. Like Neanderthals, they are the early branches of the lineage that gave rise to and subsequently merged with modern humans. However, we have known Neanderthals for about 1

50 years before obtaining any DNA sequences of Neanderthals and determining the series of anatomical features that define them. On the contrary, we didn’t know the existence of Denisovans until their DNA accidentally appeared with a tiny finger. And, so far, we have not found enough remains to truly explain their appearance.

However, with the passage of time, we have obtained more and more ancient DNA samples, which provide a clearer picture of our interaction with this mysterious lineage. Now, two new reports describe the ancient DNA and provide more details. A paper describes a modern human genome from Asia, the history of which can be traced back to the time when hybridization must occur. It provides further evidence of at least two crosses, and helps to clarify the migration of early humans across Asia. The second point confirms that Denisovans live on the Qinghai-Tibet Plateau and may have adapted to high altitude areas.

Mongolian skull

As early as 2006, mining activities in Mongolia’s Salkhit Valley discovered an apparently ancient skull. However, because it does not have any definite characteristics, people argue that it may be Neanderthal or Neanderthal. Standing person. However, preliminary DNA sequencing shows that it belongs to modern humans, and the carbon age can be traced back to approximately 34,000 years.

That was actually a critical period in human history. At that time, East Asia and East Asia (Siberia) had obvious populations, and the latter had certain connections with Western Europe and Asia. Their history is very complicated. The 40,000-year-old bones near Beijing are obviously the closest to modern East Asians, but are most closely related to the bones found in Belgium (!??!?). A 45,000-year-old Siberian skeleton does not seem to have any modern relatives, while a 24,000-year-old man from the same region discovered a population that was mixed with East Asians to produce Native American ancestors. However, the other two Siberian skeletons at about the same time period did not show this affinity, but they appeared to be Eurasia as a whole.

If you are not confused afterwards, please come back and read again.

Considering that mess, any further DNA from that era and region may be useful. Therefore, researchers have done a standard procedure that has become the processing of this ancient DNA. They first searched for sequences that matched human DNA to extract all human-like sequences. In order to eliminate the pollution of modern humans, they then looked for the most common signs of damage that occurs as DNA ages. Anything that is obviously man-made destruction is used to form a genome.

Given the age of the skull top, the end result is about the same as you would expect. Most of the mutations in DNA match those of modern humans, but there are also many regions that match Neanderthals and Denisovans. The portion of modern humans is closest to the populations of the Eastern European and Native Americans, which confirms the earlier results.

So much reproduction

But this is still as confusing as before. ” [newly described] Solkit shared alleles with Tianyuan [Beijing] The researchers wrote: “The same as the Yana individuals about 31,000 years old in northeastern Siberia, but the alleles between the Tianyuan and Yana individuals are less than the Salkhit individuals.” Overall, the researchers concluded that in the west and east The Eurasian population is separated, and there are some close relatives between the Eurasian and East Asians in the east.

But, of course, the newly described DNA of Siberia bears a striking similarity to the Belgian skeleton, which suggests that at least some Western European and Asian DNA is still being brought back into the lineage.

Other ancients

As far as Neanderthals are concerned, the new Siberian skeleton is a typical representative of the modern Asian population. About 1.7% of the DNA comes from Neanderthals. The content of Denisovan is difficult to judge, but the researchers found 18 large fragments of DNA inherited from Denisovans. The size of these genes led the researchers to conclude that hybridization took place about 10,000 years ago. This is consistent with the complete absence of Denisovan DNA in the 45,000-year-old Siberian skeleton. Moreover, the presence of Denisovan DNA is more consistent with the amount found later in East Asian bones.

Interestingly, the fragments in the new Salkhit genome do not overlap with fragments in the genomes of modern humans in Southeast Asia and the Pacific. The obvious conclusion drawn from this is that modern humans are intertwined with Denisovans in at least two different situations. Other results have shown this, but modern East Asians have DNA from both events. The Salkhit genome provides a clear separation between them.

At the same time, another paper explored the dwellings of the Denisovans-especially in the karst caves of Baishiya on the edge of the Qinghai-Tibet Plateau. At an altitude of more than 3,000 meters (nearly 11,000 feet), this is a very high environment. During the last ice age, this would be a difficult place to settle. A part of the jawbone was also found there. Although it does not produce any DNA, protein fragments indicate that its jaw belongs to Denisovan.

DNA in dirt

Most ancient DNA samples were severely contaminated by bacteria, and DNA was severely damaged and fragmented. As a result, researchers have developed various programs to help them isolate human-like DNA, and then identify ancient DNA based on its accumulated damage patterns. Gradually, people realized that these same techniques could be used even in cases of higher pollution levels and even rarer human sequences: soil samples. Therefore, although we were unable to extract DNA from the jaws, a team decided that there might be some left in the environment where it came from.

Therefore, the research team dug a hole in the sediment at the bottom of the cave and dated the different layers in order to estimate the age. Depending on the degree of damage, most layers contain mammalian DNA and are very old. Therefore, the researchers extracted human mitochondrial DNA and began to sequence it. Obviously Denisovan (Denisovan), very rarely has a small part of modern human DNA.

In general, from more than 100,000 years ago to the most recent 30,000 years ago, there are signs of Denisovan moving in. Although we don’t know that it is fixed, seasonal or sporadic, it is a long history of occupation. The researchers pointed out that in any case, 70,000 years is certainly enough time to adapt to high altitude areas. Facts have proved that this is consistent with another genetic discovery: certain genetic adaptations of Tibetans to high altitude areas are inherited from Denisovans.

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


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