The role of intentional communication in monkeys: evidence from gestural signalling in common marmosets in the wild

Human communication relies on a distinct capacity for social interaction, underpinned by cognitive skills like intentionality. To communicate intentionally, signallers produce signals with the explicit goal of influencing the behaviour or the mental states of receivers. Although long thought to be uniquely human, comparative studies have provided evidence consistent with first-order intentional communication (i.e. the signaller intends to change the recipient’s behaviour) in great apes and some monkey species. Despite being cooperative breeders like humans and renowned for their sophisticated vocal and cognitive skills, common marmosets, Callithrix jacchus , are still largely unstudied with respect to the intentional nature of their gestural communication. Here, we thus aimed to increase our understanding of common marmosets’ intentional abilities by studying communicative interactions of 20 adult individuals living in four different groups in a semiarid environment in Brazil. We especially focused on the context of grooming, a crucial context for the exchange of signals, and investigated the presence and role of gestures and whether these were aligned with intentional communication patterns. From focal animal sampling and video footage, we found that marmosets produced three different gestures (Touch, Roll-over and Present) both to initiate grooming and during ongoing interactions. These findings suggest that intentional communication plays a crucial role in the cooperative interactions of common marmosets, showing that flexible, goal-directed signalling is not restricted to the vocal domain or great apes, but may be a convergent trait driven by the demands of a cooperative social lifestyle.