Living people in Europe and Asia still carry traces of long-ago unions between Neandertals and modern humans. Two studies pinpoint genes we have inherited from our extinct cousins, including some that leave their mark on hair and skin and others that are implicated in disease. But the studies also show that those ancient mixed couples were not fully compatible genetically. The descendants of their unions—especially the males—became less fertile over time, purging many Neandertal genes from modern genomes.

For the full story, see this week's issue of Science.