
When Homo sapiens trekked out of Africa, they encountered Neanderthal populations already inhabiting the vast expanses of Europe, Asia and the Middle East. As the presence of Neanderthal DNA in most present-day people shows, interbreeding occurred, though the circumstances have remained unclear.
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.





