(CNN) – When archaeologist Ludovic Slimak unearthed five teeth in a rock shelter in the Rhône Valley from France in 2015, it was immediately obvious that they belonged to a Neanderthal, the first intact remains of the ancient species to be discovered in that country since 1979.
However, the find, nicknamed Thorin after a character from “The Hobbit,” remained a well-kept secret for nearly a decade as Slimak and his colleagues unraveled the meaning of the discovery, a complicated task that faced DNA experts. ancient against archaeologists.
“We are facing a major problem,” said Slimak, a researcher at France’s National Center for Scientific Research and Paul Sabatier University in Toulouse. “Genetics was sure that the Neanderthal we call Thorin was 105,000 years old. But we knew from the archaeological context (of the specimen) that it was between 40,000 and 50,000 years old.”
“What the DNA suggested did not match what we saw,” he added.
It took the team almost 10 years to reconstruct Neanderthal history, adding a new chapter to the long-standing mystery of why these humans disappeared around 40,000 years ago.
The research, published Wednesday in the Cell Genomics magazinediscovered that Thorin belonged to a lineage or group of Neanderthals who had been isolated from other groups for about 50,000 years. This genetic isolation was the reason Thorin’s DNA seemed to come from a time period earlier than he actually did.
Until now, geneticists thought that at the time of the extinction there was one Neanderthal population that was genetically homogeneous, but the new study reveals that at least two populations were present in Western Europe at the time, and they lived surprisingly close to each other.
“The Thorin population went 50,000 years without exchanging genes with other Neanderthal populations,” Slimak said in a press release.
“Thus, we have 50 millennia during which two Neanderthal populations, living about ten days’ walk from each other, coexisted while completely ignoring each other.”
Slimak said the discovery suggested that Neanderthal communities were small and insular, factors that could be key to understanding their extinction because isolation is generally considered an evolutionary disadvantage.
Less genetic variation could make it harder to adapt to climate change or disease, while less social interaction between groups makes it harder to share knowledge and technology.
“They were happy in their valley and did not need to move, while Homo sapiens wants to explore all the time, to see what is after this river, after this mountain. (We have) this need, this need to move and this need to build a social network,” Slimak said.
This pattern of small populations, culturally and genetically isolated from each other, was likely a major factor behind the extinction of the Neanderthals, which occurred around the same time Homo sapiens arrived in Europe, he explained.
DNA from Homo sapiens fossils from that era shows that those who arrived first interbred with Neanderthals; Traces of those encounters remain in current human populations. However, no corresponding genetic evidence of such interbreeding has been found in Neanderthal fossils from that era, including Thorin’s remains, the study noted.
Any behavior that led to this lack of genetic mixing on the one hand, along with small, isolated Neanderthal populations like the one Slimak and his colleagues identified, likely contributed to the demise of Neanderthals, said Chris Stringer, research leader in human evolution at the Natural History Museum, London, which was not involved in the study.
“Whatever the reasons for this imbalance (social, biological?), it contributed to the disappearance of the last Neanderthals, since their populations, already small, lost individuals of reproductive age to other species without any replacement occurring. in return,” Stringer said via email.
“Coupled with economic competition from newcomers for resources, this could have been a recipe for demographic collapse.”
It is unknown whether Thorin’s complete skeleton is buried in the Grotte Mandrin, as the rock shelter is known in the Rhône Valley near Malataverne, France. The remains were found near the surface in soft, unstable ground, and excavation continues slowly, Slimak said, with archaeologists taking out “one kernel at a time.” It is also unclear whether the specimen, which is male, was buried deliberately or not.
Archaeologists have excavated more of Thorin’s remains – 31 teeth, part of the jaw and five finger bones – so far. The shape of his teeth is typical of a Neanderthal, but he had two additional lower molars, a trait that sometimes suggests an inbred population, the study noted.
Initial genetic analysis suggested that Thorin was much older because his genome was different from that of other later Neanderthals, similar to that of ancient humans who lived more than 100,000 years ago.
To understand Thorin’s origins and confirm the age of his remains, the team analyzed chemical isotopes in his bones and teeth to infer what type of climate he lived in based on the water he would have drank and other factors. A Neanderthal in Europe 105,000 years ago would have enjoyed a much warmer climate than one who lived 45,000 years ago during the Ice Age.
“We worked for seven years to find out who was wrong: the archaeologists or the genomicists,” Slimak said in the press release.
Slimak has been involved in the excavation of Grotte Mandrin for more than three decades and has made a number of exciting finds in the rock shelter. It is the only known site that hosted alternating groups of Homo sapiens and Neanderthals, in addition to the oldest evidence of the use of bow and arrow outside Africa.
“Mandrin Cave continues to hold surprises,” Stringer said.
