Social network analysis shows direct evidence for social transmission of tool use in wild chimpanzees.

Claims of culture in animals have been stimulated by studies on a wide range of taxa revealing group-specific behavior patterns that remain stable through generations, consistent with different behavioral innovations spreading within groups by social transmission in a manner similar to human culture. In chimpanzees, 39 behaviors have been identified as 'cultural', because alternative genetic and environmental explanations for the observed regional variation appear less plausible. This interpretation is supported by experimental data from captive chimpanzee groups. However, there is no experimental evidence for social learning in the wild, nor has there been direct observation of social diffusion of spontaneously occurring behavioral innovations. Here, we document the spread of two novel tool-use variants, 'moss-sponging' and 'leaf-sponge re-use', in the Sonso chimpanzee community of Budongo Forest, Uganda. We use traditional network-based diffusion analysis (NBDA) to test whether these ...