An international team of researchers from Germany and the United States has mapped when the ancestors of modern humans began to interbreed with Neanderthals and how long the interbreeding phase lasted. The work appears in a preprint from BioRxiv, a platform for sharing scientific materials before peer review.
Neanderthals stand among the closest extinct relatives of Homo sapiens. The two lineages split from a common ancestor roughly half a million years ago. Over time, evidence has accumulated that interbreeding occurred as our species moved out of Africa and encountered Neanderthal populations in Europe and western Asia.
More than a decade ago, genetic analyses revealed that non-African modern humans carry a small but detectable fraction of Neanderthal DNA. Modern populations outside Africa typically retain about 1 to 2 percent of Neanderthal genetic material, a legacy that continues to influence various traits in present-day humans.
In the latest study, researchers examined over 300 ancient and modern human genomes spanning the last 45 thousand years. The results indicate a major period of interbreeding that began around 47 thousand years ago and persisted for roughly 6.8 thousand years. This extended window helped shape the Neanderthal contribution found in many contemporary genomes.
The team also explored how Neanderthal DNA endured through time within the modern human genome. They found that longer-lived Neanderthal DNA segments tended to offer potential evolutionary benefits, while shorter, rapidly sorted segments were more likely to be associated with disadvantages. This pattern suggests that natural selection shaped which Neanderthal pieces remained useful in new human environments outside Africa.
Across surviving Neanderthal genetic fragments, researchers identified associations with skin color, metabolic processes, and immune function. These links point to immediate adaptive advantages as humans faced novel climates, diets, and pathogens after migrating out of Africa.
By the end of the interbreeding period, estimates place more than 5 percent of the modern human genome of Neanderthal origin. In practical terms, roughly one in twenty Homo sapiens would have a direct Neanderthal lineage in their ancestry, illustrating the deep and lasting impact of this ancient interaction on human biology and evolution.
Beyond the core findings, the study sheds light on how different ancient populations cared for offspring and organized family life, highlighting how genetic legacies intersect with cultural practices across time. The evolving picture emphasizes that human history is a complex tapestry woven from occasional genetic exchanges, selective forces, and migrations that reshaped who we are today. The ongoing analysis of these ancient genomes continues to refine our understanding of how interbreeding events contributed to variation in traits and resilience among modern humans.