A new finding has cast doubt on the theory that ancestors of modern humans interbred with Neanderthals over thousands of years. Scientists have re-dated fossil bones from two sites in southern Spain and discovered they are much older than previously thought.

According to the new evidence, it is unlikely Neanderthals and modern humans ever lived together in the region. Researchers now think the Neanderthals had long gone before the arrival of the first Homo sapiens.

Since the 1990s experts have believed the last Neanderthals sought refuge in the Spanish peninsula and died out around 30,000 years ago. That would have provided easily enough time for the Neanderthals to mix their DNA with that of modern humans, who are believed to have colonised Spain more than 10,000 years earlier.

But the new research from Oxford University, reported in the journal Proceedings of the National Academy of Sciences, using an improved dating method indicates that the Neanderthal occupation of Spain only lasted until around 45,000 to 50,000 years ago.

Interbreeding has been suggested as the reason why traces of neanderthal DNA can be found in people living today, especially Europeans.

However, the issue has divided experts. Some believe the genetic link is due to Neanderthals and modern humans having a common ancestor which may have lived in north Africa.

Neanderthals and modern humans are distantly related sub-species of ancient human. Both are thought to have emigrated to Eurasia from Africa, but at different times.