Monkeys Make Stone Tools by Accident—and That’s Actually a Big Deal

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The discovery may offer new insights into how our distant ancestors created the first knives, axes, and spears.

By Nathan Collins

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Capuchin monkeys. (Photo: Wikimedia Commons)

Stone tools provide maybe the earliest evidence of humans’ unique mental and physical capabilities. More than two million years ago, our ancestors deliberately pounded rocks together to create rudimentary knives with sharp edges and smooth faces. Later on, they’d create the first axes and spears in much the same fashion.

Well then, prepare to be humbled: Some monkeys in Brazil do pretty much the same thing, except they do it by accident, according to a study published this week in Nature.

To be clear, there is plenty of evidence that monkeys, other animals, and even some birds deliberately craft and deploy tools, often to dig for food or break open tough-skinned fruits. There’s also evidence that members of a hominid genus other than Homo made sophisticated stone tools. But, researchers Tomos Proffitt, Michael Haslam, and their colleagues write, these latest results yield new insight into what it takes to create seemingly sophisticated stone tools—namely, not that much.

The findings follow from observations of bearded capuchin monkeys in Brazil’s Serra de Capivara National Park, a spot best known for cave paintings made as much as 25,000 years ago. Capuchins in the area were already known for using rocks to dig, pound food, and, well, other things.

These latest results yield new insight into what it takes to create seemingly sophisticated stone tools — namely, not that much.

They’re also known for pounding quartzite stones into each other. Why they do that isn’t entirely clear—nor is it clear why the monkeys in this study proceeded to lick the rocks they’d smashed—but that’s beside the point.

What’s really interesting, Proffitt, Haslam, and their team write, is what else happened while they were watching the capuchins: In the course of bashing quartzite together, stone flakes would break off, and sometimes the monkeys would bash those flakes some more. Shortly after the capuchins finished their task with the rocks, the researchers went in and collected 111 stone fragments for further analysis.

Although those samples might not look much like a proper knife or axe, they do have some of the features of early humans’ stone tools, such as sharp edges and relatively smooth faces. That doesn’t mean the monkeys created those tools on purpose, but it does suggest it didn’t take human hands or minds to create them.

The results further muddy the distinction between human and non-human behavior, the researchers argue. “The capuchin data add support to an ongoing paradigm shift in our understanding of stone tool production and the uniqueness of hominin technology,” the team writes. Capuchins’ stone tool production “goes a step further, demonstrating that the production of archaeologically identifiable flakes and cores, as currently defined, is no longer unique to the human lineage.”

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