white-faced capuchins stone tools
© Brendan Barrett/YouTubeFootage has revealed evidence that another non-human primate has entered its stone age. It shows white-faced capuchin use stone tools to crack the protective shells of nuts and other foods (pictured)
Another non-human primate has entered the Stone Age - the fourth type known to have done so. A population of white-faced capuchins living on a Panamanian island routinely use stones to smash open nuts and shellfish. Other nearby populations don't use stone tools, which might suggest that primates - perhaps including our ancestors - stumble into the Stone Age by chance.

Chimpanzees in West Africa, macaques in Thailand and several species of tufted capuchin monkey living in South America use stone tools to access food. Brendan Barrett at the Max Planck Institute for Ornithology in Radolfzell, Germany, and his colleagues have now discovered that a species of non-tufted, slender-bodied capuchin also uses stone tools (bioRxiv, doi.org/crn7).

Camera traps showed that male capuchins in one corner of JicarÓn Island use stone tools to crack open coconuts, crabs and snails. Capuchins elsewhere on JicaroÓn don't use stone tools, and neither do those on nearby islands.

Barrett thinks several factors might have encouraged the capuchins to experiment with stone tools. There are no ground-based predators on JicaroÓn, so the monkeys can afford to spend more time on the ground with their attention focused on tool use. There are also relatively few easily accessible sources of food on the island, which makes it worthwhile for the capuchins to use stones to crack open tough nuts and shells.

But that doesn't explain why capuchins elsewhere on JicaroÓn, which also experience those conditions, don't seem to use stone tools.

Perhaps it takes a single hyper-intelligent individual to make the leap and begin using stone tools, with others then copying the idea. "Good innovations are pretty rare, but if they are adaptive they can take off," says Barrett.