New research suggests that interbreeding between Neanderthals and early modern humans was heavily skewed, with male Neanderthals mating with female humans far more often than the opposite pairing. The study, published in the journal Science, offers an explanation for why Neanderthal DNA is largely absent from the human X chromosome.
Scientists analysed DNA from three Neanderthal specimens and compared it with genetic data from sub-Saharan African populations lacking Neanderthal ancestry. They found that Neanderthal X chromosomes contained 62% more modern human DNA than other chromosomes, a mirror image of the pattern seen in humans, where Neanderthal DNA is scarce on the X chromosome.
Because females carry two X chromosomes and males only one, the direction of mating affects the inheritance of X-linked DNA. If Neanderthal males mated predominantly with human females, fewer Neanderthal X chromosomes would enter the human gene pool, while more human X chromosomes would enter Neanderthal populations.
“Mating preferences provided the simplest explanation,” said Dr Alexander Platt, senior research scientist at the University of Pennsylvania and first author. The team noted that the bias likely persisted beyond initial encounters, with male Neanderthal descendants being preferred mates within human populations.
Professor Sarah Tishkoff, who led the research, said it was difficult to estimate how often interbreeding occurred, but added: “I’m just getting the sense that this was happening more than we originally speculated.” The findings challenge previous assumptions that missing Neanderthal DNA on the X chromosome was due to biological incompatibility.
