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When Homo sapiens<\/em> trekked out of Africa, they encountered Neanderthal populations already inhabiting the vast expanses of Europe, Asia \u2060and the Middle East. As the presence of Neanderthal DNA in most present-day people shows, interbreeding occurred, though the circumstances have remained unclear.<\/p>\n New research focusing on the X chromosome, one of the two sex chromosomes, in present-day people and, as revealed by ancient genomes, in Neanderthals, is providing insight into who took part in these prehistoric pairings.<\/p>\n The genetic analysis backs the conclusion that this phenomenon was primarily driven by sex between Neanderthal men and Homo sapiens<\/em> women.<\/p>\n The researchers said it is unknown why this occurred \u2013 whether \u200cby peaceful mating preference, by force or some other scenario.<\/p>\n \u201cThe preferences of either or both parties could produce these kinds of patterns, with or without the consent of the other,\u201d says geneticist Alexander Platt, of the University of Pennsylvania\u2019s Perelman School of Medicine in the US, who was co-lead author of the research published last week in the journal Science.<\/p>\n Chromosomes are thread-like structures that carry genetic information from cell to cell. In people, females carry two X chromosomes \u2013 one inherited from each parent. Males carry one X chromosome inherited from their mother and one Y chromosome from their father. For the other chromosomes, everyone has two copies \u2013 one from each parent, equally distributed across the sexes.<\/p>\n<\/div>\n