In 2010, scientists made a startling discovery about our past: About 50,000 years ago, Neanderthals interbred with the ancestors of living Europeans and Asians. Now two teams of researchers have come to another intriguing conclusion: Neanderthals interbred with the ancestors of Asians at a second point in history, giving them an extra infusion of Neanderthal DNA. The findings are further evidence that our genomes contain secrets about our evolution that we might have missed by looking at fossils alone. "We're learning new, big-picture things from the genetic data, rather than just filling in details," said Kirk E. Lohmueller, a geneticist...