A remarkable fossilized Neanderthal discovered in a cave system in the Rhône Valley, France, has revealed an ancient and previously unknown lineage of Neanderthals that remained genetically isolated for over 50,000 years. The individual, nicknamed “Thorin” after the character from J.R.R. Tolkien’s The Hobbit, lived approximately 42,000–50,000 years ago, at a time when Neanderthals were nearing extinction. This discovery, which was published on September 11 in Cell Genomics, has profound implications for our understanding of Neanderthal population dynamics, their extinction, and the complexities of their genetic structure.
Thorin’s fossil was first uncovered in 2015 at the Grotte Mandrin, a well-studied cave system that has provided invaluable insights into early human history. Grotte Mandrin is known to have housed both Neanderthals and early Homo sapiens, although not at the same time. Archaeologists initially estimated that Thorin lived around 40,000–45,000 years ago based on the sediment layers surrounding his remains. However, genomic analysis revealed something far more surprising: Thorin’s DNA was distinct from that of other late Neanderthals and closely resembled genomes from Neanderthals that lived more than 100,000 years ago.
The discovery challenges the previously held notion that late Neanderthal populations were genetically homogeneous. Until now, it was believed that by the time of Neanderthal extinction, there was only one genetically uniform Neanderthal population. The analysis of Thorin’s genome reveals that there were at least two distinct Neanderthal populations living at the time, with the Thorin lineage diverging from the rest of the Neanderthal population around 100,000 years ago. “Until now, the story has been that at the time of extinction, there was just one Neanderthal population that was genetically homogeneous,” says Tharsika Vimala, first author and population geneticist at the University of Copenhagen. “But now we know that there were at least two populations present at that time.”
Co-first author Ludovic Slimak, the researcher who discovered Thorin, explains that Thorin’s population was isolated for a long period, spending over 50,000 years without exchanging genes with other Neanderthal groups. “We have 50 millennia during which two Neanderthal populations, living about ten days’ walk from each other, coexisted while completely ignoring each other,” Slimak observes. “This would be unimaginable for a Sapiens and reveals that Neanderthals must have biologically conceived our world very differently from us Sapiens.”
To resolve the mystery of Thorin’s age and genetic relationship with other Neanderthals, the research team extracted DNA from his teeth and jaw, comparing his full genome sequence to those of other Neanderthals whose genomes had previously been sequenced. Initially, the genetic data suggested that Thorin belonged to a much older population, prompting the team to conduct further tests. They analyzed isotopes from Thorin’s bones and teeth to determine the climate he experienced. This analysis confirmed that Thorin lived during the Ice Age, ruling out the possibility that he belonged to a warmer climate population and confirming his classification as a late Neanderthal.
Thorin’s genome represents a remnant of some of the earliest Neanderthal populations in Europe. The lineage leading to Thorin separated from other late Neanderthals around 105,000 years ago, making him part of a unique and isolated group. His genetic similarities to a Neanderthal individual excavated in Gibraltar suggest that Thorin’s population may have originated from the Mediterranean region. “This means there was an unknown Mediterranean population of Neanderthals whose population spanned from the most western tip of Europe all the way to the Rhône Valley in France,” says Slimak.
One of the critical implications of this discovery is the potential role of genetic isolation in the extinction of Neanderthals. Neanderthal communities were generally small and geographically isolated, which may have limited their genetic diversity. Isolation is often detrimental to the health of a population, as it reduces their ability to adapt to changing climates, evolving pathogens, and other environmental challenges. “When you are isolated for a long time, you limit the genetic variation that you have, which means you have less ability to adapt to changing climates and pathogens, and it also limits you socially because you’re not sharing knowledge or evolving as a population,” explains Vimala.
The isolated nature of Thorin’s population highlights the fragility of Neanderthal societies. While populations with higher genetic diversity tend to be more resilient, the lack of gene flow between different Neanderthal groups could have contributed to their eventual extinction. However, to fully understand the dynamics of Neanderthal extinction and how their populations were structured, the researchers stress the importance of sequencing more Neanderthal genomes from this time period. “If we had more genomes from other regions during this similar time period, we would probably find other deeply structured populations,” says Martin Sikora, senior author and population geneticist at the University of Copenhagen.
This discovery provides a more nuanced view of Neanderthal society, one that was likely more fragmented and complex than previously understood. Thorin’s isolated lineage not only sheds light on the genetic diversity of late Neanderthals but also challenges assumptions about their social behavior and interactions. As more ancient genomes are sequenced, scientists may uncover even more layers of Neanderthal history, offering deeper insights into the factors that shaped their evolution and eventual extinction.
Source: Cell Press