Comparing hominid tools to the capuchin stones is “comparing apples and oranges,” says Sileshi Senaw, who has studied the 2.6-million-year-old stone tools of Gona, Ethiopia. Unlike the monkeys, our ancestors intentionally broke stones to create edges for cutting meat; we know that because fossil bones found at the same sites still bear the marks of these rocky blades.
“So, at first glance, the capuchin flakes don’t require us to change our thinking at all,” says Haslam. “But, what our findings do show is that there are previously unimagined ways for primates to make sharp-edged stones.”
We see tools with sharp edges and we think that they were crafted to cut and slice, because that’s what we’d use them for. Assuming deliberation, we’ve also linked the appearance of such tools to the increase in our ancestors’ mental abilities. But Haslam’s study shows that they be totally unintentional and accidental offshoot of their attempts to smash rocks together, by an animal whose brain could fit inside two shot glasses. “Maybe the earliest hominins were also making such tools unintentionally, as a byproduct of an activity unrelated to cutting anything,” he says.
Sonia Harmand from Stony Brook University agrees. Last year, she, Roche, and others described the oldest stone tools ever discovered, from deposits in Lomekwi, Kenya. With an age of 3.3 million years, such tools predate our genus Homo, and were probably made by some smaller-brained hominin. “Such flakes could have been produced by accident during rock-pounding in the past, but only hominins realized their usefulness and went on to make them deliberately,” says Harmand. And only we improved the tools, making them better and more sophisticated with time.
“We can ask why,” says Harmand. “Why did our ancestors learn to make such sophisticated stone tools, and so long ago, while chimps and monkeys never got beyond a stage? Why hominins alone have taken tool use to such an extreme?”
And why haven’t the capuchins learned to use the sharp tools that they inadvertently make? Perhaps it’s because their teeth are already great at cutting up their prey, obviating the need for any technological help. Maybe it’s that the stone-smashing sites are far away from their foraging grounds. “One of the most important characteristics of a useful tool is that you have it when you need it, as anyone who has left a phone charger at home will confirm,” says Haslam. “If we start seeing the monkeys carrying flakes away from the cliffs, in anticipation of future use, that’s when I think things might get interesting.”
He also thinks that archaeologists should spend more time looking for the works of ancient monkeys and apes. “[We should] consider what other non-human-primates in Africa and elsewhere may have been up to for the past tens of millions of years,” he says. “There is no reason why stone flakes may not be littered throughout primate history, at unknown places and times.”