A groundbreaking study has revealed that Neanderthals and modern humans (Homo sapiens) interbred for a period of around 7,000 years, starting about 50,500 years ago.
This long period of mixing has left traces of Neanderthal DNA in the genomes of present-day non-African humans, making up about 1% to 2% of their genetic material.
The new research, which analyzed ancient and modern human genomes, provides the most precise estimate yet of when this interbreeding occurred.
Scientists found the average date of Neanderthal and human mixing to be about 47,000 years ago. Previously, estimates ranged widely from 54,000 to 41,000 years ago.
The study was led by researchers from the University of California, Berkeley, and the Max Planck Institute for Evolutionary Anthropology in Germany.
Their findings were published in the journal Science.
The analysis combined data from 58 ancient human genomes, gathered from bones found across Europe and Asia, with 275 modern human genomes. The results showed that Neanderthals and modern humans didn’t just interbreed once but likely mixed multiple times over 7,000 years.
“The timing is really important because it tells us when modern humans first migrated out of Africa into Eurasia,” said Professor Priya Moorjani from UC Berkeley, one of the study’s senior authors. “It also helps us understand how humans settled in new regions by looking at the genetic evidence.”
The researchers discovered that the migration of modern humans from Africa into Eurasia was mostly completed by around 43,500 years ago. During this time, humans and Neanderthals lived alongside each other in Europe and Asia, creating opportunities for interbreeding.
Why East Asians have more Neanderthal genes
Interestingly, the study also explains why East Asians today have about 20% more Neanderthal DNA than Europeans or West Asians.
This could be because humans moving eastward around 47,000 years ago carried Neanderthal genes with them, and further mixing may have occurred.
Benjamin Peter, another senior author of the study, noted that this long period of mixing was complex. “Different groups of humans may have separated and reunited during those 7,000 years, but the shared gene flow fits the data best,” he said.
The researchers also studied areas of the human genome that contain Neanderthal genes and regions without them, called “Neanderthal deserts.” These deserts formed quickly after humans and Neanderthals interbred, likely because some Neanderthal genes were harmful to modern humans.
Early human remains from sites like Oase Cave in Romania and Tianyuan in China, dating back 40,000 years, already showed these deserts. However, beneficial Neanderthal genes, especially those related to immune function, skin pigmentation, and metabolism, were retained and passed down.
For instance, a Neanderthal gene that improves resistance to certain coronaviruses, including the virus causing COVID-19, has been found in modern humans. Other Neanderthal genes may have helped early humans adapt to colder climates and new pathogens outside Africa.
The study also touched on genes from another ancient human relative, the Denisovans. People of East Asian descent not only have a higher percentage of Neanderthal DNA but also small traces (up to 0.1%) of Denisovan DNA.
“It’s fascinating that we can look into the past and see how these genes, inherited from Neanderthals and Denisovans, have changed and shaped us over time,” said Moorjani.
The findings highlight how closely connected our ancestors were with Neanderthals. Although Neanderthals disappeared around 40,000 years ago, their genetic legacy lives on in all non-African humans today.
“This study helps us better understand how humans and Neanderthals interacted over thousands of years,” said Moorjani. “It’s incredible to see how genes from our evolutionary cousins have influenced our ability to adapt and survive.”
By uncovering the timeline and complexity of Neanderthal-human mixing, this research sheds new light on our shared history and the genetic inheritance that continues to impact us today.
