Rock-Smashing Monkeys Unintentionally Make Sharp Stone Tools

In 2014, Michael Haslam wedged between two boulders in northeast Brazil and filmed some monkeys. Oblivious to the voyeur, the monkeys—bearded capuchins—began smashing stones together. They lifted small cobbles into the air and brought these down upon a rock face, like a hammer upon an anvil. In the process, the hammer stones would often shatter. After the monkeys had gone, Haslam picked up some of these broken fragments—and was amazed. Many had sharp edges, and looked remarkably like human tools.

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