Modern humans migrated to Eurasia 75,000 years ago, where they encountered and interbred with Neanderthals. A new study published in the journal Current Biology shows that at this time Neanderthals were already carrying human DNA from a much older encounter with modern humans.

The Penn-led research team, including collaborators from Addis Ababa University, the University of Botswana, Fudan University, Hubert Kairuki Memorial University, and the University of Yaoundé, showed that an ancient lineage of modern humans migrated to Eurasia over 250,000 years ago where they interbred with Neanderthals. Over time, these humans died out, leaving a population with predominantly Neanderthal ancestry.