Illustration of an encounter between a group of Neanderthals (black) and a group of modern humans (red, top row) with offspring showing recent Neanderthal ancestry (red, bottom row), imagined as a cave art painting. DNA from bones and teeth of these early human ancestors is helping scientists understand the interactions between early Homo sapiens and the Neanderthals they encountered after migrating out of Africa. (Leonardo Iasi, MPI-EVA. Figure created with Dall-E and BioRender.com)
A groundbreaking DNA study by researchers from the University of California, Berkeley, has unveiled a fascinating chapter in human history: the interbreeding between Neanderthals and modern humans. This genetic exchange, which began around 50,500 years ago and lasted for 7,000 years, offers a glimpse into the complex interactions between these ancient populations.
That interbreeding, said the scientists, left Eurasians with many genes inherited from our Neanderthal ancestors, which in total make up between 1% and 2% of our genomes today.
The genome-based estimate is consistent with archeological evidence that modern humans and Neanderthals lived side-by-side in Eurasia for between 6,000 and 7,000 years. The analysis, which involved present-day human genomes as well as 58 ancient genomes sequenced from DNA found in modern human bones from around Eurasia, found an average date for Neanderthal-Homo sapiens interbreeding of about 47,000 years ago. Previous estimates for the time of interbreeding ranged from 54,000 to 41,000 years ago.
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These findings indicate that the initial journey of modern humans from Africa to Eurasia had mostly ended by 43,500 years ago, marking a significant milestone in human history.
“The timing is really important because it has direct implications on our understanding of the timing of the out-of-Africa migration as most non-Africans today inherit 1-2% ancestry from Neanderthals,” said Priya Moorjani, an assistant professor of molecular and cell biology at the University of California, Berkeley, and one of two senior authors of the study. “It also has implications for understanding the settlement of the regions outside Africa, which is typically done by looking at archeological materials or fossils 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, will be published in the Dec. 13 print issue of the journal Science. The two lead authors are Leonardo Iasi, a graduate student at MPI-EVA, and Manjusha Chintalapati, a former UC Berkeley postdoctoral fellow now at the company Ancestry DNA.
The extended period of interbreeding offers a compelling explanation for the intriguing genetic disparity between East Asians and their European and West Asian counterparts. East Asians carry roughly 20% more Neanderthal DNA, a legacy of interbreeding that likely occurred before their eastward migration approximately 47,000 years ago, as supported by archeological findings.
“We show that the period of mixing was quite complex and may have taken a long time. Different groups could have separated during the 6,000- to 7,000-year period and some groups may have continued mixing for a longer period of time,” Peter said. “But a single shared period of gene flow fits the data best.”
“One of the main findings is the precise estimate of the timing of Neanderthal admixture, which was previously estimated using single ancient samples or in present-day individuals. Nobody had tried to model all of the ancient samples together,” Chintalapati said. “This allowed us to build a more complete picture of the past.”
