Finding questions the evolution of Homo sapiens 0:59
(CNN) --
A child's tooth discovered in a French cave has revealed the latest evidence that humans -- Homo sapiens -- lived in Western Europe.
The discovery of the grinding wheel at the Grotte Mandrin near Malataverne in the Rhône Valley in southern France, along with hundreds of stone tools dating to around 54,000 years ago, suggests that early humans lived in Europe about 10,000 years earlier than archaeologists thought.
Furthermore, the Homo sapiens tooth was sandwiched between layers of Neanderthal remains, showing that the two human groups coexisted in the region.
These findings challenge the idea that the arrival of Homo sapiens in Europe triggered the extinction of Neanderthals, who lived in Europe and parts of Asia for some 300,000 years before disappearing.
"We often think that the arrival of modern humans in Europe led to the fairly rapid disappearance of Neanderthals, but this new evidence suggests that both the appearance of modern humans in Europe and the disappearance of Neanderthals are much more complex than that." said study co-author Chris Stringer, a professor and research leader in human evolution at the Natural History Museum in London.
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It is the first time that archaeologists have found evidence of alternating groups of Homo sapiens and Neanderthals who lived in the same place, and rotated rapidly, even abruptly, on at least two occasions, according to the study published Wednesday in the journal Science Advances.
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Previously, the arrival of the first humans in Europe was dated between 43,000 and 45,000 years ago, according to remains found in Italy and Bulgaria, not long before the last surviving Neanderthal remains were found, between 40,000 and 42,000 years ago.
This time frame had led many to believe that the arrival of Homo sapiens and the disappearance of the Neanderthals were inexorably linked.
Humans and Neanderthals, who we know from genetic analysis met and had children, leading to Neanderthal traces in our DNA, interbred over a much longer period in Europe, this study suggests.
The bumps and grooves on teeth are a bit like fingerprints to archaeologists, giving clues to ancestry and behavior.
Level E is the tooth of Homo sapiens.
Clues of humans from ancient stone tools
Did humans and Neanderthals coexist in this French cave overlooking the Rhone Valley?
The researchers don't have any hard evidence of an interaction between the two groups.
The tools found in the strata representing the occupations of Homo sapiens and Neanderthals are of different styles and do not show any sign that they have taught each other the techniques of carving or stone chipping.
Stone tools associated with humans, known as Neronian tools, are smaller than those used by Neanderthals, known as Mousterian tools.
But the authors believe it is likely that the two groups interbred in the area, even though direct contact did not occur in this particular cave.
The hundreds of stone tools found at the site suggest that the rock shelter was intensively occupied by both human groups, and was not just an occasional stopover.
Remarkably, the team was able to determine that the period between Neanderthals and early modern humans moving into the cave, 56,000 years ago, was just one year.
The researchers did this by mapping and analyzing soot deposits from fires set by humans in the cave.
"Soot is deposited on the roof of the rock shelter, and when there was a period when no one lived there, no soot was deposited," Stringer explained.
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Lead author Ludovic Slimak, a researcher at France's National Center for Scientific Research and the University of Toulouse who has worked on the site for 30 years, said he believed the two groups must have exchanged knowledge in some way.
According to Slimak, from the beginning of their occupation, modern humans used flint from hundreds of kilometers away, as evidenced by stone tools found in the cave.
That knowledge likely came from indigenous Neanderthals, Slimak explained.
"Apparently the territory was well known by Homo sapiens, and they soon found very localized sources of flint," he said.
The site in the Rhone Valley has been under excavation for three decades.
"What precisely was the interaction? We don't know. We have no idea if it was a good or bad relationship. Was it a swap group or did they have (Neanderthal) explorers showing them around and guiding them?"
The researchers dated the site's layers using radiocarbon and luminescence techniques, which measure the last time mineral grains in the rock were exposed to sunlight.
The layer containing the Homo sapiens child tooth spans from 56,800 to 51,700 years ago.
In different layers, scientists discovered another eight teeth that belonged to Neanderthals.
These Neronian stone tools were made by early modern humans who lived in Grotte Mandrin.
Untangling human history is a complicated task, but it is generally accepted that modern humans originated in Africa and made their first successful migration to the rest of the world in a single wave between 50,000 and 70,000 years ago.
Before Homo sapiens became the only survivor, different ancestral hominids existed and coexisted and there was interbreeding between the different groups of early humans.
Some of these groups, like the Neanderthals, are easily identifiable through the fossil record and archaeological remains, but others, like the Denisovans, have largely been identified by their genetic heritage.
DNA could bring history to light
Marie-Hélène Moncel, director of research at the French National Museum of Natural History in Paris, said the discovery of a single modern human tooth was not enough to definitively push back the dates of the arrival of Homo sapiens in Europe.
She said that other fossilized human remains were needed to be sure of the conclusions of this work.
"Teeth are not enough, you have to find postcranial or cranial remains to be sure," said Moncel, who was not involved in the research.
These tips tiny stone (about 0.4 inches or 10 mm in length) were manufactured by the first modern humans known in Western Europe.
It is possible that DNA - either directly from teeth or through innovative new techniques that allow DNA found in sediments to be sequenced - could flesh out the story and tell us how the pioneering group of early modern humans related to who came later and if the Neanderthals who lived in the cave had the same origins.
The DNA could show evidence of miscegenation between the two groups.
In the Bacho Kiro cave in Bulgaria, where the oldest evidence of Homo sapiens in Europe was found, the DNA of those early modern humans was 3% Neanderthal.
Teeth are well preserved in the fossil record, and their bumps and grooves are a bit like fingerprints to archaeologists, giving clues to ancestry and behavior.
According to the researchers, the shape of the tooth and its internal structure strongly suggest that it belongs to a modern human child, even though the tooth is damaged.
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