M. Haslam
By Andy Coghlan
Toolmaking may not have been such a unique feat for our immediate ancestors after all – even modern monkeys have now been found to create stone tools.
The surprising finding casts doubt on the assumption that intentional stone crafting required complex skills found only in hominins, such as changes in hand shape, coordination and cognitive skills.
It also raises the possibility that at least some of the ancient tools we attribute to human ancestors were actually the handiwork of monkeys.
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“There are Stone Age artefacts from South America that potentially overlap with the current range of capuchins, so insights from our discovery could provide greater context to this material,” says Tomos Proffitt at the University of Oxford.
For example, another recent study found archaeological evidence of 700-year-old stone tools made by monkeys in Brazil that predate the European discovery of South America.
Not so exclusive
Yet, toolmaking – especially stone knapping and the production of sharp-edged “conchoidal” flakes – had been seen as an ability exclusive to early humans and their immediate hominin predecessors, and one they used with the specific intention of making the tool in mind.
Some evidence previously suggested that West African chimps can flake stones, but these were thought to be accidental breakages.
The new study found that capuchins make sharp stones unintentionally, as part of their quest to create quartz dust, perhaps as they seek a dietary source of the trace element silicon or try to remove lichen from the rocks (see video below).
They don’t actually proceed to use the flakes as tools. Instead, the main goal appears to be generating fine quartz dust by smashing stones together, a process that produces tool-like stones as a byproduct.
“Once they have the dust, they lick it and anoint themselves with it. We have no idea why they’re doing this,” says Proffitt. “It could be medicinal, or dietary, or internal grooming – as the dust is very sharp and abrasive, so it could help to kill intestinal parasites – or it could be because they like the feel of the dust on their tongues.”
His team discovered and investigated the behaviour of capuchins in the Serra da Capivara National Park in Brazil. Proffitt’s colleagues in Brazil filmed the animals, and Proffitt analysed the sharp fragments they created (see video below).
Each capuchin creates the dust by smashing a loose quartz stone on a second one still embedded in a cliff. The impact creates dust on the surface of the embedded quartz cobblestone.
Coincidentally, it often splinters the stone used to hammer the target, generating conchoidal flakes just like those assumed until now to have been created exclusively by hominins.
In all, the researchers found 111 fragments in the area. Such a large collection would normally be taken as evidence of prehistoric hominin toolmaking activity.
“You sometimes get an isolated flake naturally, perhaps through the impact of a fallen stone, but you never get numerous flakes in one place like we did here unless there was toolmaking activity,” says Proffitt. “That’s why this has always been seen as a watershed leap in human activity.”
M. Haslam
Stone-on-stone action
“But what we find is that, by this ‘stone-on-stone’ behaviour, capuchins produce a large number of these conchoidal flakes, artefacts always associated with and considered unique to hominins,” he says.
“These artefacts are indistinguishable from some archaeological examples of intentionally flaked early hominin stone cores,” the paper says. The findings open up the possibility that collections of unintentionally flaked stones may be identified in the palaeontological record of extinct apes and monkeys.
But could it also rewrite our record of early human stone tools?
Proffitt says the discovery doesn’t mean that previously discovered stone tools were the work of monkeys, rather than early humans, especially at 3-million-year-old sites in East Africa considered the cradle of modern humans.
“Those tools are made by hominids: there’s no evidence of primate involvement and the levels of complexity used to make the flakes, and their sheer number, is far more advanced than with the capuchins,” he says.
But it could shed light on more-debated stone tool finds from the Americas.
Evolutionary insight
And it opens up new questions about how such an accidental behaviour eventually became deliberate and highly skilled in humans.
“It raises queries of what percussive behaviours led to hominins learning that flakes could be produced deliberately,” says Proffitt. “But it might also mean that if you find flakes in a 3.3-million-year-old sediment, you shouldn’t automatically assume they were made by hominids, or assume intentionality.”
“The findings overturn the long-held assumption that the presence of conchoidal fractures in a cobble means that a human intentionally worked the stone,” says Dorothy Fragaszy at the University of Georgia in Athens, who studies nut-cracking and other tool-using behaviour by capuchins.
“Together with pits on anvils, transported hammer stones and hammer-and-anvil sites revealing repeated use, conchoidal fractures on stones can no longer be taken as evidence of hominin actions,” she says. “All these features are evident in capuchins’ lithic work zones, so human brains and hands are not required to produce these artefacts.”
Other researchers also welcomed the discoveries, saying they opened up new avenues for exploring how accidental behaviour became deliberate.
“The new findings hint at how a transition from potential, initial nut-cracking behaviour towards stone-centric tool use might have occurred,” says Robert Rein, an anthropologist at the German Sport University in Cologne. “But it still leaves open the question of how the transfer from accidentally made cutting tools to actual cutting behaviour occurred.”
Journal reference: Nature, DOI: 10.1038/nature20112
Read more: Tools maketh the monkey; Did prehistoric chimps use stone tools too?
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