Why Neanderthals Likely Fathered Few Kids with Modern Humans

Humans today often carry around a small chunk of DNA from Neanderthals, suggesting we interbred with our closest known extinct relatives at some point in our history. Turns out, the Y chromosome may have been key in keeping the two lineages apart by creating conditions that might often have led to miscarriages if or when the two got together, researchers now say. In 2010, scientists first sequenced the Neanderthal genome.