On the bank of the Rhône River in southern France, in a limestone cave known as Grotte Mandrin, scientists have uncovered a puzzle so improbable it took nearly a decade to unravel.
The jawbone was the first piece. Dug from the cave sediment in 2015, it seemed unremarkable at first glance. But over the next several years, as more teeth and bones emerged, archaeologist Ludovic Slimak and his team began to suspect they had stumbled upon something extraordinary. The remains, eventually dubbed “Thorin” after the Tolkien character, belonged to a Neanderthal unlike any other known.
What they would come to discover was a new story that suggests Neanderthals were not the single, homogeneous group once imagined, but a patchwork of isolated tribes with vastly different histories.
“Until now, the story has been that at the time of the extinction there was just one Neanderthal population that was genetically homogeneous,” said Tharsika Vimala, a population geneticist at the University of Copenhagen. “But now we know that there were at least two populations present at that time.”
A Lineage Out of Time
Thorin lived sometime between 42,000 and 50,000 years ago, near the end of the Neanderthals’ presence in Europe. From the outset, Slimak had a hunch this Neanderthal was different. The tools found near the remains didn’t match those from surrounding regions. They bore the signature of a cultural tradition known as the Post-Neronian II—unique to this part of France.
But it wasn’t until researchers sequenced Thorin’s DNA that the full weight of the discovery became clear.
His genome diverged from those of other late Neanderthals around 105,000 years ago. That’s a staggering timespan. Thorin’s people had been genetically isolated for 50,000 years—even as other Neanderthals and modern humans lived just days’ walk away.
“The Thorin population spent 50,000 years without exchanging genes with other Neanderthal populations,” said Slimak. “This would be unimaginable for a Sapiens and reveals that Neanderthals must have biologically conceived our world very differently from us Sapiens.”
This isolation was also social. Unlike other humans, who build vast webs of connection and trade, Thorin’s group seems to have remained apart, both genetically and culturally.
And they may not have been alone.
Using comparative DNA modeling, researchers identified at least one other isolated Neanderthal lineage in France around the same time—at Les Cottés—suggesting these small, insular groups were more common than previously believed.
The Cousin from Gibraltar
In a surprising twist, Thorin’s closest known genetic relative was unearthed in Gibraltar. DNA from a Neanderthal found at Forbes’ Quarry—on the very southern tip of Europe—shares significant similarity with Thorin’s genome.
This suggests that Thorin’s ancestors may have migrated North from the Iberian Peninsula, carrying with them both their genes and a distinctive cultural toolkit.
“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,” said Slimak.
That genetic connection raises the possibility of a once-broader southwestern European Neanderthal population—one that eventually fractured into isolated communities, as ice age conditions and terrain splintered habitats and movement corridors.
When Evolution Stalls
What doomed the Neanderthals has long been a matter of debate: climate shifts, competition with humans, or even catastrophic events. But the discovery of Thorin reframes the extinction question through a more intimate lens.
“When you are isolated for a long time, you limit the genetic variation that you have,” said Vimala. “That 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.”
Thorin’s genome bore the marks of this constraint. Around 7% of it consisted of long runs of homozygosity—stretches of identical DNA that suggest recent inbreeding and very small group size.
“Thorin the Neanderthal is… an end of lineage. An end of a way to be human.” Slimak told IFLScience.
A Different Way to Be Human
The Grotte Mandrin site today stacks layers of human and Neanderthal history like sediment. Thorin’s bones lie nestled between cultural layers—evidence of Neanderthals reoccupying the cave after earlier visits by modern humans.
Yet there is no trace of interbreeding between Thorin’s group and Homo sapiens.
That absence speaks volumes.
“Anthropologically, these gene exchange processes are never limited to a love affair between two individuals,” the authors write in Cell Genomics. “They correspond to the alliances that human populations consciously decide to build.”
In other words, the social fabric that defines our species—sharing, marrying, mixing—may have been alien to these Neanderthal communities. Where Homo sapiens wove networks, Neanderthals like Thorin walled themselves in.
Thorin’s remains are still being excavated. Each field season brings more teeth, more bone, more clues. But even as researchers dig, the picture is already shifting. By finding him, we’ve uncovered an entire forgotten lineage—one that reminds us of the human genome’s true variety.
