NEWS - Researchers report Homo neanderthalensis, found in a cave system in France’s Rhône Valley, represents a previously undescribed ancient lineage that diverged from other known Neanderthals about 100,000 years ago and remained genetically isolated for more than 50,000 years.
Genomic analysis suggests the bones of the Neanderthal dubbed “Thorin” lived in a small, isolated community. The new discovery could shed light on the still-mysterious reasons for the species’ extinction and suggests that late Neanderthals had a broader population structure than previously thought.
“There was only one genetically homogeneous Neanderthal population going extinct, but now we know that there were at least two populations at the time,” said Tharsika Vimala of the University of Copenhagen.
The Thorin population spent 50,000 years without exchanging genes with other Neanderthal populations. Over 50 millennia, two populations of Neanderthals, living about a ten-day walk from each other, lived side by side but ignored each other.
“This is unimaginable for sapiens. Neanderthals must have biologically understood our world very differently from us, sapiens,” says Thorin’s discoverer, Ludovic Slimak, of the Université Paul Sabatier in Toulouse.
Thorin’s fossils were first discovered in 2015 in the Grotte Mandrin, a well-studied cave system that was also home to early Homo sapiens, though not at the same time. Thorin’s location in cave sediments suggests he lived around 40,000-45,000 years ago as a “late Neanderthal”.
The team extracted DNA from teeth and jaws, then compared the complete genome sequence with previously sequenced Neanderthal genomes to determine its age and relationship to other Neanderthal communities.
Surprisingly, initial genome analysis showed Thorin was much older than archaeological estimates suggested, as his genome was very different from other late Neanderthals and much more similar to the genomes of Neanderthals who lived more than 100,000 years ago.
"We worked for seven years to figure out who was wrong, the archaeologists or the genomicists," Slimak said.
The researchers then analyzed isotopes from Thorin's bones and teeth to gain insight into the climate, as late Neanderthals lived during the Ice Age, while early Neanderthals enjoyed much warmer climates. The isotope analysis showed Thorin lived in a very cold climate, which would suggest he was a late Neanderthal.
"These genomes are the remains of some of the earliest Neanderthal populations in Europe. The lineage leading to Thorin would have separated from the lineage leading to other late Neanderthals around 105,000 years ago," said Martin Sikora of the University of Copenhagen.
Thorin's genome was most similar to that of the individual excavated in Gibraltar, and the researchers speculate that the Thorin population migrated to France from Gibraltar. This means there was an unknown Mediterranean Neanderthal population that stretched from the westernmost tip of Europe all the way to the Rhône Valley in France.
Knowing that a Neanderthal community was small and isolated could be key to understanding their extinction, because isolation is generally thought to be detrimental to a population’s fitness. Connectivity is a good thing for a population to be in contact with other populations.
“When you’re isolated for a long time, you limit the genetic variation you have, you lose the ability to adapt to climate change and pathogens, it also limits you socially and you don’t share knowledge or evolve as a population,” Vimala said.
However, to truly understand how the Neanderthal population was structured and why they went extinct, the researchers say more Neanderthal genomes need to be sequenced. Genomes from other regions during this same time period could help find other structured populations.
Original research
Slimak, Ludovic et al. (2024). Long genetic and social isolation in Neanderthals before their extinction. Cell Genomics, Volume 4, Issue 9, 100593, DOI:10.1016/j.xgen.2024.100593