The ontogeny of intentional communication in chimpanzees in the wild.

The onset of intentional communication in children's first year of life represents a major milestone in human cognitive development. Similarly, it is well established that our closest living relatives, the great apes, communicate with signals characterized by at least first-order intentionality. Despite the well-documented influence of developmental experiences on socio-cognitive abilities in apes, the developmental trajectory of intentional signal use as well as effects of social exposure remain poorly understood under naturalistic conditions. Here, we addressed these issues by studying the ontogeny of intentional communication in chimpanzee infants of two subspecies (Pan troglodytes schweinfurthii/verus) and communities living in their natural environments. Overall, we found that gestures and bimodal signal combinations were most commonly accompanied by markers of intentional communication: audience checking, persistence to the goal, and sensitivity to recipient's attentional state. Within individuals, the proportion of communicative behaviours associated with goal persistence and sensitivity to attention increased with age. Cross-sectional comparisons between infants revealed an age effect on the use of audience checking. Context, interaction partner and site affiliation affected the production of specific markers irrespective of infants' age. The present study provided hitherto undocumented evidence for the development of three important markers of intentional communication in great apes. Moreover, our results suggest that social exposure impacts early intentional signal use.