Between 54,000 and 42,000 years ago, three waves of modern humans colonized Europe. That is the fundamental conclusion reached by scientists researching caves in the Rhone valley, where they uncovered evidence that Homo sapiens had to make three concerted attempts to go westwards and northwards from western Asia before settling on the continent.

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"The first two of these waves failed, but the third succeeded around 42,000 years ago," said Ludovic Slimak, director of the excavations in France. “After that, modern humans took over in Europe. The Neanderthals, who had evolved on the continent, died out.”

The study, published in the journal Plos One, is contentious since it suggests that our species' arrival in Europe took roughly 12,000 years. Far from being a quick invasion, modern humans' arrival on the continent involved a protracted journey around the Mediterranean before heading north up the Rhone Valley.

The research is especially problematic because it calls into doubt the origins of one of the most important archaic stone tool factories discovered in central France. These are known as Châtelperronian tools.

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Importantly, these tools, which are distinguished by their exquisite, narrow blades and technical manufacture, have been assigned to Neanderthal toolmakers by many, but not all, experts. According to the experts, the artifacts demonstrate that Neanderthals were capable of advanced tool production and complicated behavior.

Slimak does not conform to this view and says the tools are the handiwork of modern humans and "given their similarity to stone tools that were being made in the Middle East, we conclude they were brought there by Homo sapiens as they moved into Europe."

Early human waves lacked numbers

According to Professor Chris Stringer of London's Natural History Museum, the allegation is certain to spark debate. "This is an ambitious and provocative paper," he told the Observer. "In particular, it argues that the Châtelperronian stone industry, which is usually assumed to be the product of Neanderthals, was actually the work of Homo sapiens. Supposed associations of Neanderthal fossils with Châtelperronian tools must therefore be invalid, he is saying."

Slimak has previously argued that modern humans, who first emerged from Africa around 60,000 years ago, may have been armed with bows and arrows based on the tiny 54,000-year-old pointed stone tools resembling arrowheads discovered in the Grotte Mandrin cave in the Rhône Valley. This technique, which allows hunters to kill from a safe distance, would have given the newcomers a significant edge over the native Neanderthals.

However, after around 40 years, this initial group of modern human incomers vanished from fossil record, and the site was re-occupied by Neanderthals. Why did our initial incursion into Europe end this way if modern humans were better equipped? Similarly, why did the second wave, which most likely happened approximately 44,000-46,000 years ago, also fail?

Slimak provides an easy answer. Those early human waves just lacked numbers. He estimates the Grotte Mandrin village housed up to 100 men, women, and children. “That may not have been sufficient to maintain their biological strength and perhaps they could not exchange genes with local Neanderthals because the fertility between them was poor," he continued.

However, he opposed the notion that Neanderthals and modern people had terrible relations. In fact, every indicator suggests that the two groups were friendly. Then came the third wave, and it appears that our forefathers did have the numbers this time, Slimak added. “The third time they came in, modern humans did so with a really huge wave of people and began to build social networks, not with Neanderthals but with individual small separate groups of Homo sapiens in order to build a huge network throughout Europe. And in the end, that is what started the decline of the Neanderthals in Europe.”