Chimpanzees communicate to coordinate a cultural practice

Abstract Human culture thrives by virtue of communication, yet whether communication plays an influential role in the cultural lives of other animals remains understudied. Here, we investigated whether chimpanzees use communication to engage in a cultural practice by analyzing grooming handclasp (GHC) interactions – a socio-cultural behavior requiring inter-individual coordination for its successful execution. Previous accounts attributed GHC initiations to behavioral shaping whereby the initiator physically molds the partner’s arm into the desired GHC posture. Using frame-by-frame analysis and matched-control methodology, we find that chimpanzees do not only shape their partner’s posture (22%), but also use gestural communication to initiate GHC (44%), which requires an active and synchronized response from the partner. Moreover, in a third (34%) of the GHC initiations, the requisite coordination was achieved by seemingly effortless (i.e., no shaping or communication) synchrony. Lastly, using a longitudinal approach, we find that communication occurs more frequently than shaping in experienced dyads and less in mother-offspring dyads. These findings are consistent with the theory of ontogenetic ritualization, thereby reflecting the first documentation of learned communication in a cultural context. We conclude that chimpanzees show situation-contingent interactional flexibility in the socio-cultural domain, opening the possibility that the interplay between communication and culture is rooted in our deep evolutionary history.