"To date, most genetic data suggests that modern humans evolved in Africa 250,000 years ago, stayed put for the next 200,000 years, and then decided to disperse out of Africa 50,000 years ago and go on to people the rest of the world," said Akey.

"Our models show that there wasn't a long period of stasis, but that shortly after modern humans arose, we've been migrating out of Africa and coming back to Africa, too," he said. "To me, this story is about dispersal, that modern humans have been moving around and encountering Neanderthals and Denisovans much more than we previously recognized."