A new study indicates that Neanderthals and early Homo sapiens interbred over a broad area spanning most of Europe, the eastern Mediterranean, and western Asia. Researchers analyzed ancient genetic samples to map this hybrid zone, challenging earlier assumptions of a more localized interaction. The findings suggest repeated encounters as humans expanded from Africa.
Early humans, or Homo sapiens, and Neanderthals, known scientifically as Homo neanderthalensis, likely intermingled genetically across a wide swath of Eurasia. This interbreeding explains why most people of non-African descent carry about 2 percent Neanderthal DNA in their genomes today, with Neanderthal Y chromosome lineages largely supplanted by those from H. sapiens.
Neanderthal ancestors departed Africa around 600,000 years ago, settling in Europe and western Asia. The earliest signs of H. sapiens leaving Africa appear in skeletal remains from modern-day Israel and Greece, dating to about 200,000 years ago. There is evidence of genetic exchange in the Altai Mountains of Siberia roughly 100,000 years ago, but the primary wave of H. sapiens migration occurred after 60,000 years ago.
Two studies from 2024, drawing on ancient genomes, point to sustained gene flow lasting 4,000 to 7,000 years, beginning around 50,000 years ago. Previously, this was thought to have centered in the eastern Mediterranean, though pinpointing the exact spots proved difficult.
To clarify the geography, Mathias Currat at the University of Geneva and colleagues examined 4,147 ancient genetic samples, the oldest about 44,000 years old, from over 1,200 sites. They measured the prevalence of Neanderthal-derived genetic variants, or introgressed alleles, transferred through hybridization.
"The idea was to see whether it is possible using the patterns of Neanderthal DNA integration in past human genomes to see where integration took place," Currat explained.
Their analysis revealed a gradual rise in Neanderthal DNA proportions moving away from the eastern Mediterranean, leveling off after approximately 3,900 kilometers both westward into Europe and eastward into Asia. Computer simulations delineated a hybrid zone encompassing most of Europe, the eastern Mediterranean, and western Asia—aligning with nearly all known Neanderthal fossil sites in western Eurasia, excluding the Altai region.
"We were quite surprised to see a nice increasing pattern of introgression proportion in human genomes resulting from what we guess is the out-of-Africa human expansion," Currat noted. "What we see seems to be a single continuous pulse—a continuous series of interbreeding events in space and time."
Notably, the Atlantic fringe, including western France and much of the Iberian Peninsula, falls outside this zone, despite Neanderthal presence there. This might indicate no interbreeding occurred, or that such events are not captured in the samples.
Leonardo Iasi from the Max Planck Institute for Evolutionary Anthropology in Leipzig called the results intriguing, suggesting "interactions between populations may have been geographically widespread." He added that the study depicts "repeated interactions between modern humans and Neanderthals across a broad geographic range and over extended periods of time."
Chris Stringer at the Natural History Museum in London praised the work for upending the idea of a single hybridization hotspot in western Asia. Instead, as H. sapiens dispersed in growing numbers, "they mopped up small Neanderthal populations they encountered along the way, across virtually the whole known Neanderthal range."
The research appears in a preprint on bioRxiv (DOI: 10.64898/2026.01.06.697899v1). Limited ancient DNA from areas like the Arabian Peninsula hinders assessing the zone's full extent southward.