A new study published in the journal Science has revealed that interbreeding between Neanderthals and modern humans was strongly sexually biased.[1] The researchers found that most of the offspring came from pairings of Neanderthal males and modern human females.[1][2] X chromosome analysis showed a 62 percent relative excess of modern human heritage on Neanderthal X chromosomes, confirming this pattern.[1][3] Using mathematical modeling, the researchers found that this sexual bias was the result of preferential mate selection rather than purely demographic processes.[1] An alternative explanation suggests that there may have been fewer women in the last Neanderthal groups, leading to greater mobility and contact with modern human women.[3] However, the study does not provide direct evidence of the specific behavior or nature of these interactions, but provides genetic evidence of a sex bias in the cross between the two species.[3]