Recent research has significantly refined our timeline of interbreeding between modern humans and Neanderthals, establishing this complex interaction beginning about 50,500 years ago and lasting approximately 7,000 years. This groundbreaking study indicates how this interbreeding contributed to the genetic legacy present within contemporary non-African populations, which still carry approximately 1-2% Neanderthal ancestry.
According to scientists from the University of California, Berkeley, along with collaborators from the University of Rochester and the Max Planck Institute for Evolutionary Anthropology, the interbreeding period sheds light on the initial migration of humans out of Africa and the subsequent behavioral patterns when modern humans encountered Neanderthals.
“The timing is really important because it has direct implications on our understandings of the history of human migration,” stated Priya Moorjani, assistant professor of molecular and cell biology at the University of California, Berkeley, and one of the lead authors of the study.
Using genomic data from both contemporary humans and 58 ancient genome sequences gathered from human remains found across Eurasia, the research provides clarity on the initial interbreeding interactions. These findings suggest modern humans and Neanderthals coexisted and interacted closely during this period, leaving behind genetic markers still discernible today.
Earlier estimates of the timeline for Neanderthal interbreeding ranged from 54,000 to 41,000 years ago, but the new analysis indicates the most accurate date for interbreeding occurs around 47,000 years ago. The research team indicated this new timeline aligns with archaeological evidence, indicating the two groups shared their habitats for about 6,000 to 7,000 years.
Notably, the findings can also elucidate why genetic traces of Neanderthals differ among contemporary human populations. For example, East Asians possess roughly 20% more Neanderthal genes compared to Europeans and West Asians due to the mixing of genes prior to humans dispersing eastward around 47,000 years ago.
Benjamin Peter, another lead researcher from the University of Rochester, emphasized the complexity of these interactions: “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. But our data fit best with the idea of one shared period of gene flow.”
One of the standout aspects of this research involved the discovery of Neanderthal deserts—regions within the human genome devoid of Neanderthal genes, indicating potential gene incompatibilities which may have posed serious threats to survival.
“Areas lacking Neanderthal genes developed rapidly, which suggests the presence of lethal Neanderthal gene variants,” noted Leonardo Iasi, who also contributed to the study. “Early modern human samples older than 40,000 years lack any ancestry traces from these genetic deserts.”
This discovery builds upon previous work by Moorjani, who pioneered methods to estimate the timing of Neanderthal gene flow using ancient DNA samples. The new study built on these methods, choosing to analyze more complex models to demonstrate the lengthy interbreeding time rather than assuming it occurred sporadically.
The joint effort by the UC Berkeley and MPI-EVA teams not only highlighted when interbreeding occurred but also examined the functional descendants of Neanderthal genes within modern humans. Many of these inherited alleles have been linked to important traits like immunity and skin pigmentation—features particularly advantageous for Homo sapiens as they navigated diverse and harsh environments outside Africa.
“Neanderthals thrived outside Africa, possessing unique adaptations to Ice Age climates and local pathogens,” Moorjani explained. “These genes allowed modern humans to adapt and survive when they encountered similar challenges upon migrating to these environments.”
Scientific inquiry surrounding how interbreeding has shaped modern human genetics continues to evolve, with increasing evidence supporting the relevance of Neanderthal genetic segments across diverse human populations.
Looking forward, researchers like Moorjani are interested not only in Neanderthal ancestry but also the influence of other ancient hominins, such as Denisovans, on modern human genetics. “It’s fascinating to trace how variants from our previous evolutionary neighbors changed and adapted through time. This research paves the way for a broader exploration of how ancient interactions have shaped us,” she said.
Published studies cover analyses of human genome sequences found within archaeological discoveries, including notable findings from the skull of Zlatý kůň, discovered in the Czech Republic, which contributed invaluable data for pinpointing the timelines of interbreeding.
The collaborative findings from the recent studies not only confirm broader timelines for Neanderthal interactions but provide insights on the genetic improvements modern humans acquired through this process. The fresh perspectives on our genetic past pave the path for numerous future explorations aimed at unlocking the mysteries of our evolutionary history.
