Ed Yong’s recent story about this cleverest of creatures:

Rock-Smashing Monkeys Unintentionally Make Sharp Stone Tools

What this says—and doesn’t say—about the evolution of human technology

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.

For millions of years, humans and our ancestors have been using one stone to hammer flakes away from another, leaving behind with sharp edges or tips. Haslam knew such tools well. He had studied them in Australia, Honduras and India, and even lectures on their evolution at the University of Oxford. “And here were monkey by-products, which I’d seen being made, that had all the hallmarks of basic flaked tools,” he says.

Let’s be clear: The monkeys are not intentionally making knives. They never use the sharpened stones to slice or cut. “They have thousands of sharp stones lying around, and the most we’ve seen a monkey do with them is put one in its mouth,” says Haslam.

Still, their inadvertent creations suggest that our own stone technology may have had similar accidental beginnings. “We need to look again at the criteria used for identifying simple stone flakes as being solely the product of the human lineage, or of human planning, or of human need for cutting edges,” says Haslam. “We’ve now doubled our known number of stone-flaking primate lineages, from one to two.”