Chimpanzees attribute agency to virtual animals, but not to self-propelled shapes

Discriminating agents from inanimate objects is essential for predicting others' behaviour. Although chimpanzees (Pan troglodytes) differentiate between agents and objects, the cues underlying this ability remain unclear. We investigated chimpanzees' agency attribution using a virtual-environment paradigm in which they interacted with four competitors varying in two putative agency cues: self-propulsion and animal-like morphology. We measured facial, vocal and gestural emotive responses directed at these competitors as behavioural markers of agency attribution. Chimpanzees showed clear evidence of attributing agency. The effect of self-propulsion was not significant, but there was a strong effect of morphology: subjects responded more strongly to animal-shaped virtual competitors than to geometric shapes. This pattern resembles that shown by human infants and adults: they, too, identify entities with animal features as agents, but self-propelled movement without cues of internal control is not enough to denote agency for these populations. These converging results point to a shared, morphology-based mechanism guiding agentive responses in chimpanzees and humans.