On the rocky slopes of Brazil’s Serra da Capivara National Park, a group of small monkeys called capuchins pound against each other on rocks. One seizes a large stone, seizes it with both hands and strikes it down like a hammer on another stone. Then the monkey bends down and carefully licks the remaining pulverized quartz. After a few minutes, this hammering shatters the stone and produces a few shards called “flakes” that look almost exactly like the sharp stone knives and scrapers made by the ancestors of mankind millions of years ago.
Zoology researcher Tiago Falótico of the University of São Paolo saw it all and videotaped it. This monkey behavior had never been observed before, so he passed it on to his colleague Tomos Proffitt of the University of Oxford’s Primate Archeology Group. In a newspaper before Naturethey describe the astonishing discovery that apes are capable of making the equivalent of Stone Age humanoid tools, albeit unintentionally.
Previous researchers had seen the capuchins pounding stones, but assumed it was a form of aggression, intended to scare off enemies. But the videos Proffitt and his colleagues have collected show something very different. “It wasn’t aggressive behavior and instead seemed to be aimed at crushing the quartz into dust so it could be ingested and rubbed on the skin,” Proffitt told Ars via email.
The researchers remain unsure as to why the monkeys lick the stones they hammered. Perhaps they eat lichens they have loosened, or perhaps they seek minerals in the form of silicon powder from the rock. Regardless of why they do it, what is certain is that the apes’ inadvertent production of sharp stones called conchoidally fractured flakes could change our understanding of how tool use evolved in humans.
Evolutionary biologists have suggested that our ancestors started making specialized flake tools more than 3 million years ago because they were undergoing some kind of cognitive change. This change would have affected both their intelligence and hand coordination, ultimately leading to a diverse toolkit. It’s even possible that these early humans created their first flake tools in the same way these capuchins did, by smashing stones together and accidentally creating smaller pieces ideal for cutting and scraping. Anyway, it seemed that this style of tool making was unique to humans and our ancestors.
But we now know that apes can make the same kinds of stone tools as early hominids, despite diverging from us on the evolutionary tree long before we were smashing rocks together in the early Paleolithic. “It raises interesting questions about the minimum level of cognitive complexity and how complex a hand has to be to produce a large number of sharp-edged conchoidally fractured flakes,” Proffitt told Ars. “We now have evidence that another species is capable of producing exfoliated rocks that share features that we previously thought were unique to hominins.”
He’s not suggesting that monkeys are about to leave Planet of the Apes on us. Instead, this discovery means we may need to revise our understanding of why human ancestors developed stone tools. Clearly, we’re not alone in our ability to crush rocks and create sharp flakes. So something else was at play that set our species on their current path, and we need new hypotheses to explain it.
What is certain is that this discovery does not call into question the long history of hominids using flake tools. We have ample evidence dating back millions of years that our ancestors made flake tools and used them for butchery, based on telltale markings we’ve found on bones at ancient campsites. But it could explain the 40,000 to 20,000-year-old rock chips discovered in the Americas millennia before we have evidence of human habitation there. It’s possible that capuchins smashed and licked rocks in Brazil long before humans arrived, leaving behind debris that looks confusingly like Stone Age human tools.
However, watching the Capuchins use stones as hammers “raises interesting questions about what stone tool technology might have looked like before this technology appeared in the archaeological record,” Proffitt said. Many species may have produced pungent flakes. But for some reason, only humanoids decided to start using them as tools.
Nature2016. DOI: 10.1038/nature20112
Frame image by M. Haslam