In a genomic study of more than 300 genomes, researchers traced the period during which Neanderthals interbred with modern humans, beginning about 50,500 years ago and lasting about 7,000 years until Neanderthals began to disappear. identified. This interbreeding left Eurasians with many genes inherited from their Neanderthal ancestors. These genes collectively make up 1% to 2% of our genome today.
Neanderthal. Image credit: Mauro Cutrona.
To date, sequencing of the Neanderthal and Denisovan genomes has revealed substantial gene flow between these ancient humans and the ancestors of modern humans, but scientists believe that Neanderthal They also report that ancestry is unevenly distributed across the genome.
Furthermore, while certain regions of the genome (known as archaic deserts) are completely devoid of Neanderthal ancestry, other regions may be due to beneficial adaptive mutations, leading to Neanderthal There are many variants of this.
However, much about the nature of this ancient mixture remains unknown, including the role that evolutionary forces such as genetic drift and natural selection played in shaping these patterns.
“This timing is critical because most non-Africans today have 1% to 2% of their ancestry from Neanderthals, which directly impacts our understanding of the timing of out-of-Africa migration.” said Dr. from the University of Berkeley. Priya Moorjani.
“This also has implications for understanding habitat in areas outside Africa, which is usually done by examining archaeological materials and fossils from different parts of the world.”
“Longer durations of gene flow may help explain, for example, why East Asians have about 20% more Neanderthal genes than Europeans or West Asians.”
“If modern humans had migrated east about 47,000 years ago, as the remains suggest, they would have already mixed in Neanderthal genes.”
In this study, Dr. Moorjani and his colleagues analyzed genomic data from 59 ancient individuals and 275 diverse modern individuals sampled between 45,000 and 2,200 years ago.
They examined the frequency, length, and distribution of Neanderthal ancestral segments over time.
They found that most of Neanderthal gene flow resulted from a single, shared, long-term gene flow that probably occurred between 50,500 and 43,500 years ago. This is consistent with archaeological evidence for overlap between modern humans and Neanderthals in Europe.
Furthermore, their findings indicate that Neanderthal ancestors underwent rapid natural selection, both positive and negative, particularly on the X chromosome, within 100 generations after gene flow.
“We show that the period of admixture was very complex and may have taken a long time,” said Dr. Benjamin Peter, a researcher at the University of Rochester and the Max Planck Institute for Evolutionary Anthropology.
“Different groups may have separated between 6,000 and 7,000 years, and some groups may have continued to mix for longer periods.”
“But a single shared period of gene flow fits the data best.”
Dr. Manjusha Chintalapathi, a researcher at the University of California, Berkeley, said: “One of the major discoveries is the precise estimation of the time of admixture with Neanderthals, which until now has only been possible with a single ancient sample or modern individual. It was estimated using
“No one had ever tried to model all the ancient samples together.”
“This allowed us to build a more complete picture of the past.”
“We identified several areas where Neanderthals were present at high frequencies, perhaps because they were beneficial to early modern humans as they began to explore new environments outside of Africa. I guess.”
“These include genes related to immune function, skin pigmentation, and metabolism.”
“On the other hand, there are large regions of the genome that are completely devoid of Neanderthal ancestry.”
“These regions formed rapidly after gene flow and were absent even in the earliest modern human genomes from 30,000 to 45,000 years ago.”
“Many of the Neanderthal sequences were harmful to humans and therefore may have been actively and rapidly selected by evolution.”
“Human diversification outside of Africa may have begun during or shortly after the Neanderthal gene influx, which could partially explain differences in levels of Neanderthal ancestry among non-African populations. “We may be able to reconcile our dates with archaeological evidence for the presence of modern humans in the southeast, where Asia and Oceania evolved around 47,000 years ago,” Dr Peter said. spoke.
“Studying more ancient genomes from Eurasia and Oceania could improve our understanding of when humans spread to these regions.”
of result appear in the diary science.
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leonardo NM palm others. 2024. Neanderthal ancestry through time: Insights from ancient and modern human genomes. science 386 (6727);doi: 10.1126/science.adq3010
Source: www.sci.news
