When Neanderthals and our species had babies together, the prehistoric pairings tended to follow a distinct pattern: Neanderthal dads and moms who were Homo sapiens — the same as modern humans.
Since 2010, scientists have known that Neanderthals and our ancestors had offspring together, and those hybrid babies passed down their genes to many present-day people. But the idea of “archaic introgression,” episodes when ancient species of humans interbred and exchanged genes, remained somewhat distant and abstract.