Rock-smashing monkeys make flakes like early stone tools

Call them knockoffs. Rock-smashing monkeys in Brazil make stone flakes that look a lot like tools made by our ancient ancestors.

Scientists watched as Capuchin monkeys in a national park pounded stones against each other, splitting off sharp-edged flakes that resemble cutting tools used by the forerunners of humans.

The monkeys ignored the flakes, focusing on the damaged stones instead. So they clearly weren’t deliberately making them as tools. But if ancient monkeys did the same thing, their unintentional handiwork could be mistaken for deliberate tool-making by human ancestors, researchers said.

The scientists are not suggesting that any stone tools attributed so far to human forerunners were instead made by monkeys, said Tomos Proffitt of Oxford University in England. Those tools, which date back as far as 3.3 million years ago, are more complex than what the Brazilian monkeys make, he said in a telephone interview.

But as scientists look for earlier and earlier tools, their findings may begin to resemble the monkey flakes more strongly, said Proffitt, lead author of a study released Wednesday by the journal Nature. And the new work shows that such flakes are not exclusively the calling card of our ancient ancestors, called hominins, he said.

If somebody finds very old simple flakes, “you can’t assume it is hominin. You have to say it might be produced by an extinct monkey or ape,” Proffitt said.

Our African ancestors used sharp-edged stone flakes for butchering and skinning animal carcasses, as well as cutting up tough plant material. To show such flakes were humanmade tools, scientists seek evidence like wear marks on the edges or nearby animal bones with marks from butchering.

Proffitt and his co-authors studied capuchin monkeys in the Serra da Capivara National Park. They examined the flakes and damaged rocks and compared them to artifacts from human ancestors. It’s not clear why the monkeys smash rocks together, he said.

Scientists long thought tool-making was confined to our branch of the evolutionary family tree, the Homo group. But last year, scientists reported finding 3.3-millon-year-old tools much older than any known member of Homo. Maybe they were made by some smaller-brained forerunner hominin, like the creature best known for the skeleton nicknamed “Lucy.”