As if Neanderthals weren’t already mysterious enough, a new study adds a new layer to our understanding of Neanderthal populations. Apparently, some of them lived in genetic and social isolation for more than 50,000 years. The groundbreaking research, conducted on a Neanderthal individual discovered in Grotte Mandrin in Mediterranean France, uncovers genetic divergence and highlights the role of isolation in the disappearance of Neanderthals.

The Grotte Mandrin Neanderthals

The Grotte Mandrin rock shelter in southern France has long been a treasure trove for archaeologists. It contains multiple sedimentary layers spanning tens of thousands of years, preserving the history of both Neanderthals and early modern humans. In 2015, during an excavation at the site, a remarkable find was made: the partial remains of a Neanderthal individual. He was dubbed “Thorin,” a reference to a Tolkien character in the Lord of the Rings universe. This Neanderthal is among the most well-preserved individuals found in France.

Thorin’s remains, including cranial and dental fragments, date back to approximately 50,000 years ago. The site’s rich archaeological context provided evidence that Thorin lived during the final millennia of Neanderthal existence. But it wasn’t just the discovery of Thorin’s remains that intrigued researchers. What made this find particularly significant was the genetic data recovered from his teeth. They revealed a story of long-term isolation that had not been previously documented in late Neanderthal populations.

“The Thorin population spent 50,000 years without exchanging genes with other Neanderthal populations,” says co-first author and discoverer of Thorin, Ludovic Slimak, CNRS researcher of Université Toulouse III – Paul Sabatier.

It’s not like this population was living far away from others either, says Slimak.

“We have 50 millennia during which two Neanderthal populations, living about ten days’ walk from each other, coexisted while completely ignoring each other. This would be unimaginable for a Sapiens and reveals that Neanderthals must have biologically conceived our world very differently from us Sapiens.”

So shocking the data seemed wrong

Thorin was found in the same layer as other objects and structures from 40-45,000 years ago, so archaeologists estimated that that was Thorin’s age as well. But the genetic data suggested that Thorin was very different from Neanderthals who lived in that period and suggested the individual more closely resembled the genomes of Neanderthals who lived more than 100,000 years ago.

“We worked for seven years to find out who was wrong — archaeologists or genomicists,” says Slimak.

To get to the bottom of this, researchers turned to a third type of information: isotopes. Basically, isotopes in Thorin’s bones and teeth hold clues regarding the climate in which the individual lived. In this case, the data showed Thorin was indeed a Late Neanderthal, living in a cold climate around forty thousand years ago.

“This genome is a remnant of some of the earliest Neanderthal populations in Europe,” says population geneticist and senior author Martin Sikora of the University of Copenhagen. “The lineage leading to Thorin would have separated from the lineage leading to the other late Neanderthals around 105,000 years ago.”

Genetic Isolation for 50,000 Years

Traditionally, Neanderthal extinction theories have focused on external factors, such as climate change, volcanic eruptions, or competition with modern humans. However, the genetic isolation of Neanderthal groups introduces the possibility that internal factors also played a critical role. For neanderthals, their social structures, limited mobility, and inbreeding might have posed an added challenge. The lack of interbreeding with other Neanderthal groups or early modern humans could have left isolated populations like Thorin’s vulnerable to extinction.

Genomic analysis showed high levels of inbreeding, which is consistent with a small, isolated population. Thorin’s lineage appears to have been cut off from other Neanderthal groups for millennia, with little to no genetic exchange occurring between these isolated communities. This isolation, combined with small group sizes, likely contributed to the genetic uniqueness of Thorin’s population.

This discovery suggests that, by the time Thorin lived, there were multiple, genetically distinct Neanderthal populations scattered across Europe. These populations might have been culturally and geographically close but genetically isolated, indicating a complex population structure among late Neanderthals. Why didn’t they interbreed at all for so long? It’s not entirely clear. It could be geographic barriers or climatic changes, but it could also be social behaviors that prevented these Neanderthal groups from interbreeding.

Neanderthals are even more surprising than we thought

The myth that Neanderthals were unthinking brutes has long been disproven. They appear to have been every bit as intelligent and culturally capable as humans. Yet the reasons for their disappearance are all the more mysterious.

Thorin’s population was not the only isolated Neanderthal group during this period. Other Neanderthals, such as those from the Mezmaiskaya and Chagyrskaya caves in Siberia, also show signs of small group sizes and genetic isolation. Together, these findings suggest that Neanderthals were not a single, cohesive population but rather a collection of fragmented groups, each facing their own challenges.

This cultural separation could have been another factor in the isolation of Neanderthal populations. While early modern humans likely had broader social networks and exchanged ideas and technologies across larger distances, Neanderthals appear to have been more limited in their interactions with other groups.

Thorin’s population represents one of the last groups of surviving Neanderthals in Europe. As isolated as they were, these Neanderthals managed to persist until around 40,000 years ago, just before Neanderthals disappeared from the archaeological record. The discovery of Thorin’s genome suggests that these final populations were living in increasingly fragmented and isolated communities. They faced the pressures of inbreeding, environmental change, and competition with modern humans.

By studying individuals like Thorin, researchers are beginning to piece together the final chapters of Neanderthal history. It is becoming increasingly clear that Neanderthal extinction was not a single event but rather the culmination of many factors.

Long genetic and social isolation in Neanderthals before their extinction, Cell Genomics (2024). DOI: 10.1016/j.xgen.2024.100593. www.cell.com/cell-genomics/ful … 2666-979X(24)00177-0