Researchers analyzed Neanderthal genomes and found a 62% relative excess of modern human ancestry on Neanderthal X chromosomes compared to other Neanderthal chromosomes, indicating sex-biased mating between Neanderthal men and modern human women.

Published in Science, the study provides a genomic explanation for uneven Neanderthal DNA distribution across genomes and sheds light on ancient human–Neanderthal interactions.

The results suggest the mating bias was not a one-off event but persisted within populations after initial hybridizations, pointing to a long-running pattern of Neanderthal male and modern human female pairings.

While the social context remains unknown, the authors propose mate preference as a plausible driver and also consider demographic factors like imbalanced populations as possible contributors.

The Science paper, released in late February 2026, is led by evolutionary geneticist Alexander Platt and has broader implications for understanding how interspecies interactions have influenced human evolution.

The researchers hope this work will spur further genetic investigations into the drivers of interspecies mating patterns and their evolutionary implications.

Experts caution conclusions are tentative, as factors like meiotic drive or varying interbreeding dynamics could also shape Neanderthal DNA in non-African modern humans.

Four explanations were considered for the X-chromosome pattern; researchers argue mating preference is the most plausible among them, though not definitive.

Co-authors note that these findings illustrate how intimate relationships in ancient populations were shaped by social and cultural interactions, not solely survival advantages, with implications for future work with anthropologists and evolutionary psychologists.

The team emphasizes that the finding reflects mating preferences rather than attractiveness assumptions, noting that interspecies matings would have been viewed differently by each group.

Independent experts suggest that mate preference aligning with historical patterns in evolution would not be surprising, though social dynamics remain uncertain.

The authors acknowledge multiple evolutionary factors—natural selection, sex biases, mate preference, and sex-specific migration—that could contribute to the patterns and call for deeper study of Neanderthal social structures and gender roles.