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Rich circumstantial evidence suggests that the extensive behavioural diversity recorded in wild great apes reflects a complexity of cultural variation unmatched by species other than our own1-12. However, the capacity for cultural transmission assumed by this interpretation has remained difficult to test rigorously in the field, where the scope for controlled experimentation is limited13-16. Here we show that experimentally introduced technologies will spread within different ape communities. Unobserved by group mates, we first trained a high-ranking female from each of two groups of captive chimpanzees to adopt one of two different tool-use techniques for obtaining food from the same 'Pan-pipe' apparatus, then re-introduced each female to her respective group. All but two of 32 chimpanzees mastered the new technique under the influence of their local expert, whereas none did so in a third population lacking an expert. Most chimpanzees adopted the method seeded in their group, and these traditions continued to diverge over time. A subset of chimpanzees that discovered the alternative method nevertheless went on to match the predominant approach of their companions, showing a conformity bias that is regarded as a hallmark of human culture11.
Owing to logistical and ethical constraints on translocation and other field experiments, social learning in apes has been studied experimentally predominantly in captive populations. Over 30 such experiments in the past 15 years have provided evidence of imitation and other forms of social learning17. However, the extent to which the cultural interpretation of data from the wild is supported by this work remains contentious14-15,18, principally because all of the controlled experiments have been restricted to one-to-one learning, typically relying on a human model. The extent to which the social learning documented is sufficient to sustain traditions has thus remained unclear.
Our experiment bridges the gap between population-level studies of wild apes and one-to-one social learning experiments by (1) extending the experimental approach to the group level, (2) focusing on ape-to-ape transmission, and (3) using a powerful 'two-action' methodology17. In this approach, individuals see a given task completed using one of two possible techniques, allowing the extent to which their own subsequent behaviour matches the demonstration to be systematically measured. We studied three groups of chimpanzees: a control group exposed to a new task with no expert present,...