The Neanderthals' survival at what may have been their last refuge at Gibraltar, at the southern tip of Spain, for far longer than currently assumed suggests our ancestors may not have driven them to extinction.
"While the rest of where they lived was getting colder, down here at the southernmost tip of Europe there were still little pockets of Mediterranean climate, so the world of the Neanderthals there didn't change that much," researcher Clive Finlayson, an evolutionary biologist at The Gibraltar Museum and lead author of the Nature article, told LiveScience.
The researchers speculate the Neanderthals may have fallen victim to a cooling of the climate, which deteriorated their environment too rapidly for them to adapt.
An expanded window of time in which modern humans and Neanderthals might have interacted reopens possibilities they may have interbred, experts added.
More like wrestlers
The researchers investigated Gorham's Cave, where Neanderthal stone tools such as spear tips had been found more than 50 years ago.
Neanderthal tools differ from those of modern humans by the way the rock is chipped off and trimmed and by their very size and weight.
"Neanderthals were more like wrestlers, while modern people are in comparison more like long-distance runners," Finlayson explained. "Neanderthals made heavy spears for close-quarter ambush hunting of large animals such as rhinos or elephants. Tools of modern people were lighter and perhaps more portable for people who were on the move."
By carbon-dating charcoal from newly excavated hearths at Gorham's Cave, the scientists found Neanderthals might have survived there until 28,000 years ago, and maybe as recently as 24,000 years ago.
While the rest of Europe got colder as glaciers advanced, the area around Gibraltar back then "resembled a European Serengeti," Finlayson said.
Leopards, hyenas, lynxes, wolves and bears lived among wild cattle, horses, deer, ibexes, oryxes and rhinos, all surrounded by olive trees and stone pines, with partridges and ducks overhead, tortoises in the underbrush and mussels, limpets and other shellfish in the waters.
This natural richness of wildlife and plants in the nearby sandy plains, woodlands, shrublands, wetlands, cliffs and coastline probably helped the Neanderthals to persist, he added.
Indeed, evidence at the cave shows the Neanderthals likely used it as a shelter on and off "for 100,000 years," Finlayson said.
As the climate cooled, the forested and semi-forested areas Neanderthals were best adapted to were replaced in northern Europe by tundra advancing from the north and steppe advancing from the east.
Modern humans, who were more mobile than Neanderthals, might have been better suited for the open expanses of the newer terrain.
"The key was physique, which for Neanderthals did not change fast enough," Finlayson said.
Prior findings suggested the Neanderthals went extinct in Europe 30,000 years ago, while modern humans arrived in Western Europe some 35,000 years ago after having migrated through Eastern Europe and the Middle East, where Neanderthals also lived.
The fact the span between the arrival of modern humans and the extinction of the Neanderthals was so relatively brief hinted that Neanderthals got out-competed.
Finlayson's team's findings suggest instead that Neanderthals survived after modern humans moved in, and as the environment changed due to climate shifts, Neanderthals faded away.
While about 5,000 years seems to separate modern humans and Neanderthals in Gorham's Cave, evidence of modern humans at other locations nearby has been dated to 32,000 years ago.
If Neanderthals lasted longer than once thought, the question of whether Neanderthals and modern humans interbred is raised again, said paleoanthropologist Eric Delson at the American Museum of Natural History and at Lehman College in New York.
Past digs in the area had uncovered what some researchers claimed was the skeleton of a hybrid child.
"How could there be a hybrid, if the last Neanderthal died out thousands of years before this child was born? But if it can be shown that Neanderthals were still living near Gibraltar some 24,000 years ago, that part of the hesitancy disappears," Delson said.
Still, he added, questions remain about whether the skeleton really does resemble a Neanderthal's.
Future research can delve deeper into Gorham's Cave or other nearby caves, Finlayson said.
"They might be lucky enough to find some Neanderthal fossils, which would help document who made the artifacts," Delson said.
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