> Curiously, the exchange of DNA appears to have been one way — meaning modern human DNA seems to have not entered Neanderthal genomes. "There is little evidence of gene flow in the reverse direction at this time — that is, Homo sapiens to Neanderthal," Stringer noted.

I recently read the book "The Naked Neanderthal" by the paleoanthropologist Ludovic Slimak, who suggests that this phenomenon, as well as the extinction of the Neanderthals in general, is due to the social domination, including military domination, of the Neanderthals by Homo sapiens, who were much better than Neanderthals at manufacturing weapons, for example. So Neanderthal women would mate with Homo sapiens men in Homo sapiens communities, either voluntarily or involuntarily, whereas Homo sapiens women would not mate with Neanderthal men in Neanderthal communities, either voluntarily, because they had a much lower social status, or involuntarily, because Neanderthals did not win wars with Homo sapiens.