Neanderthal men showed a strong preference for mating with modern human women, according to a new analysis of ancient DNA published in *Science*. This mating bias is evident in the genetic patterns observed across the X chromosomes of both Neanderthals and modern humans. The study, led by researchers at the University of Pennsylvania, examined the X chromosomes of the few complete Neanderthal genomes available and compared them to those of contemporary African populations.

They found a significant excess of modern human sequences on the Neanderthal X chromosome, mirroring the pattern seen in modern human genomes where large stretches lack Neanderthal DNA. This suggests that mating between Neanderthal males and modern human females was more common than the reverse, leading to a genetic signature where the Neanderthal X chromosome is largely absent in both populations.