New studies show humans and Neanderthals interbred over 7,000 years

On Thursday, the Max Planck Institute for Evolutionary Anthropology in Leipzig reported on studies revealing that modern humans and Neanderthals interbred around 47,000 years ago, with evidence suggesting that this mixing event lasted about 7,000 years.

A team led by archaeogeneticists from the Max Planck Institute, including Arev Sümer, Kay Prüfer, and Johannes Krause, analyzed high-quality DNA from bone fragments found in Ranis, Germany, and Zlatý kůň, Czech Republic. They examined the genomes of seven Homo sapiens individuals who lived approximately 45,000 years ago, making them the oldest Homo sapiens genomes ever sequenced.

"We have here the oldest genomes of a Homo sapiens, i.e., a modern human—this is also relevant for other disciplines!" Johannes Krause, director of the Department of Archaeogenetics at the Max Planck Institute for Evolutionary Anthropology, stated, according to Tagesschau.

The researchers discovered that these individuals possessed around 2.9% Neanderthal DNA in their genomes, indicating recent interbreeding between the two species. The Neanderthal DNA found in these early modern humans is consistent with the Neanderthal DNA identified in all present-day populations outside Africa.

In a separate study published in Science, researchers analyzed genomic data from 334 modern humans, including 275 present-day individuals and 59 ancient genomes ranging from 45,000 to 2,200 years old. They found that Neanderthal ancestry entered the human genome over an extended period between 50,500 and 43,500 years ago.

"Our analysis shows the Out-of-Africa migration must have completed by 43,500 years ago and earlier waves may have been from individuals that have not contributed to living, non-African individuals," Priya Moorjani, a researcher at the University of California, Berkeley, and lead author of the Science paper, said, according to Science News.

The findings suggest that modern humans and Neanderthals interbred in a single, common, and long-term gene flow event after Homo sapiens left Africa. This mixing event likely occurred around 47,000 years ago and lasted about 7,000 years.

"These are not really two species, they're two groups," Priya Moorjani told The Independent. "That means the differences that we imagine between these groups to be very big were actually very small genetically, and they could mix with each other for a long period and were living side by side."

The studies also revealed that the Neanderthal DNA inherited by modern humans included genes related to immune function, skin pigmentation, and metabolism. These genetic variants may have provided advantageous adaptations, helping early modern humans survive in new environments outside Africa.

"The explanation for that is probably that the Neanderthals had lived in Europe 300,000 years before Homo sapiens arrived. They had adapted to the viruses and bacteria that were prevalent in Europe. So when Homo sapiens came, it was really good to get those genes, so you had something to resist with," Laurits Skov, a researcher involved in the study, said, according to Videnskab.

The research indicates that the modern human population that interbred with Neanderthals was likely a small, contiguous group of a few hundred individuals who inhabited a larger area in Central Europe over several generations and maintained kinship relations.

The findings also suggest that the interbreeding occurred shortly after the ancestors of all non-African people migrated out of Africa and into Eurasia. The timing of this mixing event aligns with archaeological evidence of the overlap between modern humans and Neanderthals in Europe.

"These results provide us with a deeper understanding of the early pioneers who settled in Europe," Krause, co-lead author of the study, stated.

Furthermore, the studies show that modern humans and Neanderthals interbred several times, with evidence of concentrated gene flow during this period.

This article was written in collaboration with generative AI company Alchemiq