Behavioural biology: Stones that could cause ripples.

Abstract

Monkeys have been observed pounding stones and unintentionally forming sharp-edged, tool-like fragments. This deliberate breakage raises questions about the evolution of intentional stone modification. See Letter p.85 In Brazil there are archaeological sites with abundant accumulations of chipped stones. The accumulation and the stones, if discovered in a three-million-year-old context in Africa, might be taken as evidence of an early stone tool culture. But in this instance the perpetrators have been caught in the act. This study reports observations of wild bearded capuchin monkeys (Sapajus libidinosus) deliberately breaking stones in Brazil's Serra da Capivara National Park. Why they do this is not clear, though they sometimes lick or sniff the crushed stone, prompting speculation that that they may be ingesting powdered quartz or lichens. However, the monkeys do not appear to use the sharp edges to cut or scrape other objects. These monkeys are the only non-hominin primates to interact with stone so frequently, and the fact that they produce accumulations of worked stone similar to those presumed elsewhere to represent the work of early hominins could help to inform interpretation of the human Palaeolithic record.