Early humans migrated from Africa and mated with Neanderthals much earlier than previously thought, a new study has claimed.
It had been assumed that homo sapiens evolved in Africa 300,000 years ago and then a small group migrated to other continents about 70,000 years ago.
Now it is believed the migration away from Africa took place 270,000 years ago.
The key was a 120,000-year-old Neanderthal fossil found in a German cave called Hohlenstein-Stadel in 2013. Its DNA, scientists concluded, was inherited from an ancestor who lived 150,000 years earlier.
Fossils show that Neanderthals were rather different to early humans. They had thicker bodies and a heavy brow.
What is known is that the African migrants interbred with Neanderthals, but they then disappeared.
However some of their DNA was found in later generations of Neanderthals.
The key was to be found in DNA samples, in particular mitochondrial DNA which is passed through the maternal line.
The latest analysis goes some way to solving a riddle which has puzzled paleontologists since the 19th century, which is how Neanderthals are related to homo sapiens.
It was these samples which enabled scientists to conclude that the migrants did breed with Neanderthals who were already present in Europe.
Johannes Krause, the director of the Max Planck Institute for Human History in Germany, has spent more than a decade trying to stitch together the story.