When archaeologist Ludovic Slimak unearthed five teeth in a rock shelter in France’s Rhône Valley 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.
But the once-in-a-lifetime discovery — which earned the Neanderthal owner the nickname Thorin, after a character in “The Hobbit” — remained a closely guarded secret for nearly a decade as Slimak and his colleagues worked to unravel its significance. A daunting task that pitted ancient DNA experts against archaeologists.
“We faced a big problem,” said Slimak, a researcher at France’s National Center for Scientific Research and Paul Sabatier University in Toulouse. “Genetics was certain that the Neanderthal we called Thorin was 105,000 years old. But we knew from the archaeological context (of the specimen) that it was somewhere between 40,000 and 50,000 years old.”
“What the DNA was suggesting was not in line with what we saw,” he added.
It took the team nearly 10 years to piece together the intriguing Neanderthal story, adding a new chapter to the long-standing mystery of why these humans disappeared some 40,000 years ago.
The research, published Wednesday in the Cell Genomics Journaldiscovered that Thorin belonged to a lineage or group of Neanderthals that had been isolated from other groups for about 50,000 years. This genetic isolation was the reason why Thorin’s DNA appeared to come from an earlier period in time than it 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.
“Thorin’s population spent 50,000 years without exchanging genes with other Neanderthal populations,” Slimak said in a press release. “We therefore have 50 millennia during which two Neanderthal populations, living about a ten-day walk from each other, coexisted in complete ignorance of each other.”
Slimak said the discovery suggests that Neanderthal communities were small and insular — factors that may be key to understanding their extinction, because isolation is generally considered an evolutionary disadvantage.
Less genetic variation can 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 didn’t need to move, whereas Homo sapiens all the time wants to explore, to see what’s beyond this river, beyond this mountain. [Nós temos] this need, this need to change ourselves, 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 Neanderthals, which occurred around the same time that Homo sapiens arrived in Europe, he said.
DNA from Homo sapiens fossils from that time period shows that these early individuals interbred with Neanderthals — traces of these encounters remain in modern human populations. However, no corresponding genetic evidence of this interbreeding has been found in Neanderthal fossils from that time period, including Thorin’s remains, the study noted.
Whatever behavior led to this lack of genetic mixing on one side, along with small, isolated Neanderthal populations like the one Slimak and his colleagues identified, likely contributed to the Neanderthals’ demise, said Chris Stringer, research leader in human evolution at the Natural History Museum in London, who was not involved in the study.
“Whatever the reasons for this imbalance, it contributed to the demise of the last Neanderthals, as their already small populations were losing reproductive-age individuals to other species without any replacement in return,” Stringer said in an email.
“Coupled with economic competition from newcomers for resources, this could have been a recipe for demographic collapse,” he added.
It’s unclear whether Thorin’s complete skeleton is buried inside Grotte Mandrin, as the rock shelter in France’s Rhône Valley is known. The remains were found near the surface in soft, unstable soil, and the excavation is proceeding slowly, Slimak said, with archaeologists picking up “one grain at a time.” It’s also unclear whether the specimen, which is male, was buried deliberately or not.
Archaeologists have unearthed more of Thorin’s remains: 31 teeth, part of his jaw and five finger bones, so far. The shape of his teeth is typical of a Neanderthal, but he had two extra lower molars — a trait sometimes suggestive of inbreeding, the study noted.
Genetic mystery solved
Initial genetic analysis suggested that Thorin was much older because his genome was different from other later Neanderthals, resembling the genomes 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 kind of climate he lived in based on the water he would have drunk and other factors. A Neanderthal in Europe 105,000 years ago would have enjoyed a much warmer climate than one living 45,000 years ago during the Ice Age.
“We worked for seven years to figure out who was wrong — archaeologists or geneticists,” 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 discoveries at the rock shelter. It is the only known site to have been home to alternating groups of Homo sapiens and Neanderthals, and the oldest evidence of the use of bows and arrows outside of Africa.
“Grotte Mandrin continues to bring surprises,” Stringer said.
This content was originally published in Solution to archaeological mystery helps explain the extinction of Neanderthals on the CNN Brasil website.
Source: CNN Brasil
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