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 peninsular and finally died out around 30,000 years ago.
That would have provided enough time for Neanderthals to mix their DNA with that of modern humans, which are believed to have colonised Spain more than 10,000 years earlier.
However, the new research, using an improved dating method, indicates 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.
Neanderthals and modern humans are distantly related sub-species of ancient humans.