European Neanderthals were on the verge of extinction even before moderns humans arrived on the scene, a DNA analysis has shown.
According to the Swedish and Spanish team, most Neanderthals in the region died off as early as 50,000 years ago, although a small group later recolonised central and western Europe, where they survived for another 10,000 years before modern humans appeared.
"The fact that Neanderthals in Europe were nearly extinct, but then recovered, and that all this took place long before they came into contact with modern humans came as a complete surprise to us," says Love Dalén, associate professor at the Swedish Museum of Natural History.
"This indicates that the Neanderthals may have been more sensitive to the dramatic climate changes that took place in the last Ice Age than was previously thought."
The researchers found that the genetic variation among European Neanderthals was extremely limited during the last ten thousand years before they disappeared. However, older Neanderthal fossils from both Europe and Asia showed much greater genetic variation, as might be expected from a species that had been abundant in an area for a long period of time.
"The amount of genetic variation in geologically older Neanderthals as well as in Asian Neanderthals was just as great as in modern humans as a species, whereas the variation among later European Neanderthals was not even as high as that of modern humans in Iceland," says Anders Götherström, associate professor at Uppsala University.
The findings cast serious doubt on the generally-accepted view that Europe was populated by a stable Neanderthal population for hundreds of thousands of years up until modern humans arrived - and that modern humans may have been responsible for their decline.