When Homo sapiens migrated out of Africa, the world outside was far from empty.
Some parts were inhabited by archaic human species including the Neanderthals and Homo erectus, both of them older forms of human that had migrated out of Africa long before modern humans.
Today the Neanderthals and Homo erectus are both extinct. But both were still alive when our ancestors left their African home continent. Professor Svante Pääbo of the Max Planck Institute explains the genetic evidence showing that we met the Neanderthals.