The research was reported Wednesday in the journal Cell.
"This is very cutting-edge population genetics work," said geneticist Spencer Wells, a National Geographic explorer. "This 'whole genome' analysis the team performed is really revolutionizing our understanding of human history. It's an exciting time to be in the field, but it's difficult to interpret all the new data."
Wells said the oldest modern human skull, found in Ethiopia, dates to 195,000 years ago. For more than 150,000 years, then, humans shared the planet with cousin species.
Despite all the amorous advances, though, only one group survived — us.
Akey said: "As we were conquering the world, we also conquered similar human populations that were dying out."