Intentional gesturing increases social complexity by allowing recipient's understanding of intentions when it is inhibited by stress.

Examining the links between intentional communication and social relationships provides insights into the cognitive skills needed to manage a differentiated set of social bonds. Great apes gesture intentionally, but how this intentionality relates to sociality is still unclear. Stress in the form of dominant audience members inhibits understanding of intentions, downgrading cognition to understanding of behaviour, but intentional communication may enable social bonding in stressful conditions. We examined the associations between gestural communication, sociality, stress and the outcome of interactions in wild chimpanzees. Social network size was positively associated with intentional but not non-intentional communication. When a dominant bystander was present with whom the recipient was weakly bonded, and gesturing was non-intentional, recipients produced avoidance response toward signallers to whom they were weakly bonded, indicating understanding of behaviour. Signallers used intentional gestures more frequently to recipients who were stressed, and intentional gestures evoked approach behaviour by the recipients, indicating understanding of intentionality. These results suggest that the presence of dominant bystanders is stressful, inhibiting understanding of intentionality. However, intentional gestures facilitate social bonding by allowing understanding of intentions. The cognitive skills underpinning intentional gestures may therefore play a key role in enabling primates to meet the demands of sociality. This article is part of the theme issue 'Cognition, communication and social bonds in primates'.