Mellars writes, "Expression at this level of complexity would be almost inconceivable in the absence of complex language systems and in the absence of brains structured very similarly, if not identically, to our own."
He adds that most experts agree that modern humans such as the Aurignacians had fully complex language, because the experts believe all modern humans today have complex language skills. Even today's most isolated populations, whether they be Australian Aborigines or Eskimos, possess the same levels of complexity of grammar.
Mellars said complex language would have given modern humans a crucial, competitive edge over Neandertals.
"The power to communicate with people makes almost all activities more efficient, from coordinating hunting activities to passing on information about the location of food resources," he said.
He suggests information on the location of wood for fuel would have been particularly important for surviving winter.
"We're right in the middle of the last major glacial period and the landscape in Europe was almost treeless," he added.
The study suggests the timing of the Aurignacians' arrival in Europe may have pressed home their language advantage.
Climatic records indicate temperature oscillations of up to 8 degrees Celsius (14 degrees Fahrenheit) around the time the Neandertals (also spelled "Neanderthals") disappeared.
"Perhaps because they had better technology, were more innovative, and because of the language, modern humans may have been able to adapt to these rapid climatic changes quicker than the Neanderthals," Mellars said.
He adds that Neandertals had survived similar climatic oscillations in the past, when they wouldn't have faced modern human competition.
In contrast with Homo sapiens, there is no direct archaeological evidence for complex language among Neandertals, though most experts agree they probably did possess some form of basic language.
"It may well be that Neanderthals didn't have tenses and subjunctive clauses, and probably didn't have complicated sentences," Mellars added.
And while archaeological finds show that Neandertals were skillful toolmakers and hunters, they don't appear to have produced any art or personal ornaments.
Mellars believes this lack of "symbolic activity" is characteristic of a people who lacked skilled communication and creative imagination and who had difficulty in being innovative. To us, he says, Neandertals may have appeared autistic.
"There may have been some kind of mutation in the brain after modern humans split off from Neanderthals," he added.
Previous studies indicate that no traces of Neandertal mitochondrial DNA (a type of DNA generally passed down by females) are present in human populations today. Mellars believes the DNA findings bolster the argument that Neandertals and modern humans were separate species.
"That's the strongest evidence that Neanderthals were incapable of interbreeding with modern humans," Mellars added. "Ninety percent of DNA specialists think that Neanderthals were a different species."
Chris Stringer is head of human origins at the Natural History Museum in London. Stringer, who was not involved with the study, said he agrees with most of Mellars's arguments.
"I agree that the evidence still largely supports an influx of modern humans into Europe, followed by the replacement of the Neanderthals with, at most, a trivial amount of gene flow [interbreeding] between the populations," he said.
"The modern-human adaptive pattern allowed Homo sapiens to cope better with rapid climate changes than the archaic 'natives' of Eurasia, such as the Neanderthals," Stringer added.
Stringer, however, takes a different view from Mellars as to when competition between Neandertals and modern humans first began. Stringer says Homo sapiens probably started to penetrate Neandertal territories in Europe and western Asia from at least a hundred thousand years ago.
For Mellars, it was the advanced language and behavior of the modern humans that "provided the foundations of all the later developments in culture and advanced civilizations in Europe and elsewhere."
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