When we interbred with Neanderthals, they were usually the fathers
New Scientist
February 26, 2026
AI-Generated Deep Dive Summary
When modern humans (Homo sapiens) and Neanderthals interbred, there was a strong preference for male Neanderthals mating with female Homo sapiens. This conclusion comes from genetic evidence analyzed by researchers, focusing on the X chromosomes of both species. While other chromosomes show significant mixing between the two hominins, the human X chromosome has almost no Neanderthal DNA, and the Neanderthal X contains more modern human DNA than their non-sex chromosomes.
The study considered several possible explanations for this bias. Hybrid incompatibility was ruled out since the X chromosomes from both species appear compatible. Natural selection also didn’t seem to play a significant role as the retained DNA on the Neanderthal X is mostly non-functional. Cultural factors, such as differences in how males and females moved between groups, were also explored but couldn’t fully explain the observed bias.
The most plausible explanation remaining is a mating preference. Male Neanderthals may have preferred female Homo sapiens, or vice versa, leading to this pattern over generations. This suggests that interbreeding was not random but influenced by specific social dynamics. While the study provides compelling evidence, researchers caution that more data is needed to fully understand why this bias occurred and whether the matings were consensual or forced.
This discovery adds an intriguing layer to our understanding of human evolution. It implies that early humans and Neanderthals interacted in complex ways, with social preferences shaping genetic outcomes. The findings also highlight how deeply intertwined the fates of these two species were during their coexistence, leaving a lasting impact on the genomes of modern non-Africans who carry traces of Neanderthal DNA.
This study not only sheds light on ancient interbreeding patterns but also emphasizes the importance
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Originally published on New Scientist on 2/26/2026