Interbreeding between Neanderthals and humans lasted 7,000 years

Dec. 13 () –

A new analysis of ancient DNA from modern humans in Europe and Asia determines that interbreeding with Neanderthals started 50,500 years ago and lasted about 7,000 years.

That miscegenation, which It ended when the Neanderthals began to disappearleft Eurasians with many genes inherited from our Neanderthal ancestors, which in total make up between 1% and 2% of our current genomes.

Genome-based estimation is consistent with archaeological evidence that modern humans and Neanderthals lived side by side in Eurasia for between 6,000 and 7,000 years.

The analysis, which included current human genomes as well as 58 ancient genomes sequenced from DNA found in modern human bones from across Eurasia, found an average date for interbreeding between Neanderthals and Homo sapiens of about 47,000 years ago. Previous estimates of the timing of interbreeding ranged between 54,000 and 41,000 years ago.

The new dates also imply that the initial migration of modern humans from Africa to Eurasia practically It ended 43,500 years ago.

“The timing is really important because it has direct implications on our understanding of the timing of migration out of Africa, as Most modern non-Africans inherit 1-2% of Neanderthal ancestry“said Priya Moorjani, associate professor of molecular and cellular biology at the University of California, Berkeley, and one of the two senior authors of the study.

“It also has implications for understanding the settlement of regions outside of Africa, which is typically done by looking at archaeological or fossil materials in different regions of the world.”

The genome analysis, also led by Benjamin Peter of the University of Rochester in New York and the Max Planck Institute for Evolutionary Anthropology (MPI-EVA) in Leipzig, Germany, It was published in the journal Science.

EAST ASIANS HAVE MORE NEANDERTHAL RELATIONSHIP

The longer duration of gene flow may help explain, for example, why East Asians have about 20% more Neanderthal genes than Europeans and Western Asians. If modern humans moved east about 47,000 years ago, as archaeological sites suggest, They would have already had Neanderthal genes intermingled.

“We show that the period of mixing was quite complex and may have taken a long time. Different groups could have separated during the period of 6,000 to 7,000 years and some groups may have continued mixing for a longer period of time,” said Peter in a statement. “But a single shared period of gene flow fits the data better.”

“One of the main findings is the precise estimation of the timing of admixture with Neanderthals, which was previously estimated using individual ancient samples or in present-day individuals. No one had attempted to model all the ancient samples together,” Chintalapati said. “This allowed us to build a more complete picture of the past.”

In 2016, Moorjani pioneered a method to infer the timing of Neanderthal gene flow using often incomplete genomes from ancient individuals. At that time, only five archaic Homo sapiens genomes were available.

For the new study, Iasi, Chintalapati and their colleagues used this technique with 58 previously sequenced genomes from ancient Homo sapiens who lived in Europe, western and central Asia over the past 45,000 years and the genomes of 275 contemporary humans around the world to provide a more precise date: 47,000 years ago.

Instead of assuming that gene flow occurred in a single generation, they tested more complex models developed by Iasi and Peter to establish that interbreeding spanned over about 7,000 years, rather than being intermittent.

The timing of interbreeding between Neanderthals and modern humans was corroborated by another independent study carried out by MPI-EVA researchers and has been published in the journal Nature. That study, an analysis of two newly sequenced genomes of Homo sapiens who lived about 45,000 years ago, He also found a date of 47,000 years ago.

“Although ancient genomes were published in previous studies, they had not been analyzed to look at Neanderthal ancestry in this detailed way. We created a catalog of segments of Neanderthal ancestry in modern humans. By analyzing all of these samples together, we inferred that the period of gene flow was around 7,000 years,” Chintalapati said.

“The Max Planck group sequenced new samples of ancient DNA that allowed them to directly date Neanderthal gene flow. And they arrived at a chronology similar to ours.”

The UC Berkeley/MPI-EVA team also analyzed regions of the modern human genome that contain genes inherited from Neanderthals and some areas that lack Neanderthal genes entirely. They found that areas lacking Neanderthal genes, the so-called archaic or Neanderthal deserts, developed rapidly after the two groups interbred, suggesting that some Neanderthal gene variants in those areas of the genome They must have been lethal to modern humans.

The first samples of modern humans that are more than 40,000 years old (samples from the Oase Cave in Romania,

Ust’-Ishim in Russia, Zlaty kun in the Czech Republic, Tianyuan in China and Bacho Kiro in Bulgaria) They already contained these deserts in their genomes.

“We found that the first modern humans from 40,000 years ago have no ancestry in deserts, so these deserts may have formed very quickly after gene flow,” Iasi said.

“We also analyzed changes in the frequency of Neanderthal ancestry over time and across the genome and found regions that are present at high frequency, possibly because they carry beneficial variants that were introduced by Neanderthals.”

Most of the high-frequency Neanderthal genes are related to immune function, skin pigmentation and metabolism, as reported in some previous studies.

A variant of the immune gene inherited from Neanderthals confers protective effects against the coronavirus that causes COVID-19, for example. Some of the Neanderthal genes involved in the immune system and skin pigmentation actually increased in frequency in Homo sapiens over time, implying that they may have been advantageous to human survival.

“Neanderthals lived outside Africa in harsh Ice Age climates and adapted to the climate and pathogens of these environments. When modern humans left Africa and interbred with Neanderthals, some individuals inherited Neanderthal genes that presumably them allowed them to adapt and thrive better in the environment,” Iasi said.

“The fact that we find some of these regions already in samples from 30,000 years ago shows that some of them adapted immediately after introgression,” Chintalapati added.

Other genes, such as the gene that confers resistance to coronaviruses, may not have been useful immediately, but became useful later. “The environment changes and then some genes become beneficial,” Peter said.