Another non-human primate has entered the Stone Age – the fourth type known to have done so. One population of white-faced capuchins living in Panama routinely use stones to smash open nuts and shellfish. Other nearby populations don’t make use of 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, strongly built capuchin monkeys living in South America use stone tools …