Children, but not capuchins, rationally integrate social and physical information when deciding which actions to copy

Unlike other primates, young children have been shown to exhibit seemingly irrational overimitation—faithfully copying unnecessary steps from a demonstration. We tested 3- to 5-year-old children (N = 39) and capuchin monkeys (N = 21) on a causal reasoning task in which a sequence of two actions was demonstrated, followed by reward production. We manipulated (1) causal plausibility and (2) the degree and nature of demonstrator intentionality, to explore the hypothesis that children—but not capuchins—integrate information about demonstrator intent and causal relations to infer which actions are necessary. We compared both species’ behavior to Bayesian computational models with the same varying social and physical expectations. Our results suggest that both species can learn from causal demonstrations, and that their copying behavior is affected by both the demonstration’s causal plausibility and the demonstrator’s communicative cues, but that children may be unique in interpreting communicative cues as having pedagogical intent.