Stone blades found in a Siberian cave once occupied by Neanderthals bear a striking resemblance to tools made by the ancient human species in eastern Europe – more than 3000 kilometres to the west.
The finding, published in the Proceedings of the National Academy of Sciences, lends weight to the idea that Neanderthals made the intercontinental trek to this far-flung region not once, but twice.
The Chagyrskaya Cave, at the foothills of the Altai Mountains, is a fossil- and artefact-rich time capsule of palaeolithic life, which seems to have been occupied by Neanderthals alone.
This sets it apart from the more famous Denisova Cave – situated in a neighbouring valley just 100 kilometres further east – which was occupied at various times over about 250,00 years by Neanderthals, anatomically modern humans, and the Denisovans, an archaic human group named after the cave.
Archaeologist Kseniya Kolobova from the Institute of Archaeology and Ethnography in Novosibirsk, Russia, and her colleagues have unearthed 74 Neanderthal bones – the most of any cave in the region – from a single package of sediment in the Chagyrskaya Cave.
But Neanderthal bones aren’t all they found. In amongst around 250,000 animal fossils and plant remains, were some 90,000 artefacts, including stone and bone tools.
The team analysed more than 3,000 stone blades and found that they resemble flaked stone tools known as Micoquian blades.
“It’s one of those classic Neanderthal-type artefacts,” says human origins researcher Richard (Bert) Roberts, from the University of Wollongong in Australia, who co-led the study.
But, he says, Micoquian blades aren’t usually found in Siberia. None have been found in the Denisova Cave, for instance. “Central and eastern Europe is really the heartland of this Micoquian tradition.”
This suggests that the Neanderthals who migrated eastward into Siberia to occupy the Chagyrskaya Cave could trace their origins to this region of Europe, more than 3,000 kilometres to the west.
The fact that the Denisova Cave lacks such distinctive tools also suggests that Neanderthals arrived in Siberia in at least two waves.
“In this case we were lucky because the archaeology tells a story,” says Roberts. “Often artefacts don’t tell you enough. They look too similar to one another to tease apart the story.”
“It’s a nice piece of the puzzle that they add,” says Stéphane Peyrégne from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who was not involved in the study.
Geneticists including Peyrégne have previously suggested that Neanderthals migrated to Siberia twice, because late Neanderthal occupants of the Denisova Cave are more closely related to their European relatives than they are to earlier occupants of the same cave.
The archaeological evidence in the current study fits that story.
The Chagyrskaya Neanderthals probably belonged to a later migration, although the researchers haven’t nailed down firm timelines yet.
Feldspar deposits in the fossil-bearing layer of the Chagyrskaya Cave date to between 59,000 – 49,000 years ago.
But a genome reconstructed from ancient DNA extracted from a finger bone at the site is estimated to be closer to 80,000 years old.
“That’s still a point of puzzlement for all of us,” says Roberts.
One explanation could be that the Neanderthal bone was somehow reworked into the layer from an older deposit, although they are yet to find any sediment of the right age.
Another possibility is that the genetic age estimate is off because of a difference in mutation rate or generation time in Neanderthals compared to humans. Sequencing of additional genomes from other individuals in the cave could resolve the conundrum, says Roberts.
A preliminary analysis of the Chagyrskaya genome – which Peyrégne is involved in – shows that is it more closely related to Neanderthals in Europe than to an earlier Neanderthal from the Denisova cave, again pointing to at least two separate groups that reached Siberia.
The tools also provide clues to why Neanderthals made the epic journey.
Neanderthals used Micoquian blades to slice meat and scrape the hides of animals they hunted. The Chagyrskaya Neanderthals could have been following migrating bison or horse herds through central Asia towards the vast Siberian plains.
“It’s an interesting study,” says archaeologist Mark Moore from the University of New England in Armidale, Australia, who was not involved in the work. “They’ve attempted to incorporate both the archaeological analysis for the stone tools with what’s emerging with the ancient DNA analyses, which we didn’t have even five years ago.”
The story is far from complete. Roberts is keen to know whether other sites – perhaps along the route through central Asia, also have Micoquian blades.
Knowing that they had the capacity to travel to Siberia, Roberts says they might also have trekked further, perhaps into China.
“It’s just yet another indication that Neanderthals were just as creative, just as industrious, just as explorative in their nature as modern humans were,” he says.