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

The study, published in Science, provides a genomic explanation for uneven Neanderthal DNA distribution across human and Neanderthal genomes, offering insight into ancient human-Neanderthal interactions.

Results imply that the mating pattern was not a one-time event but persisted within populations after initial hybridizations, indicating a sustained bias toward 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.

Co-authors note that these findings show intimate relationships in ancient populations were shaped by social and cultural interactions, not solely survival advantages, potentially guiding future collaborations with anthropologists and evolutionary psychologists.

The work, led by evolutionary geneticist Alexander Platt, was published in Science and sheds light on how interspecies interactions have shaped human evolution.

Experts caution that conclusions are tentative, as factors like meiotic drive or varying interbreeding dynamics across episodes could also influence the Neanderthal genetic legacy in non-African modern humans.

Researchers hope this study motivates further genetic investigations into the drivers of interspecies mating patterns and their implications for human evolution.

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

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

Mathematical models support sex-biased mating as plausible, though migration differences or selection pressures remain possible explanations requiring more assumptions.

The study does not determine why these patterns occurred or whose preferences drove them; researchers seek broader genetic clues to infer social structure, movement, and gender roles in Neanderthal groups.