Wild bearded capuchins process cashew nuts without contacting caustic compounds.

Complex and flexible food processing was a key element for the evolutionary success of hominins, enlarging the range of exploitable foods while enabling occupation of new habitats. Only a few primate species crack open encased food by using percussive tools and/or avoid physical contact with irritant compounds by removing the structures containing them. We describe, for the first time, how a population of bearded capuchin monkeys (Sapajus libidinosus) accesses the nutritious kernel of cashew nuts avoiding the caustic chemicals protecting it. Two processing strategies, namely rubbing/piercing and stone tool use, are used according to maturity of the nuts. The frequency of cashew nuts processing increases with capuchin age, and the same set of processing strategies appears to be absent in other capuchin populations, making cashew nuts processing an excellent candidate for social transmission.