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 analysing grooming handclasp (GHC) interactions-a socio-cultural behaviour requiring interindividual coordination for successful execution. Previous accounts attributed GHC initiations to behavioural shaping, whereby the initiator physically moulds 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 synchrony. Lastly, using a longitudinal approach, we find that for GHC initiations, communication occurs more frequently than shaping in experienced dyads and less in mother-offspring dyads. These findings are consistent with ontogenetic ritualization, thereby reflecting first documentation of chimpanzees communicating to coordinate a cultural practice. We conclude that chimpanzees show interactional flexibility in the socio-cultural domain, opening the possibility that the interplay between communication and culture is rooted in our deep evolutionary history.

Keywords: Pan troglodytes; communication; coordination; culture; grooming handclasp.

Figure 1.

Moyo (back) and Tess (front) engaged in a palm-to-palm GHC (back-view: photo by Zoë Goldsborough).

Figure 2.

Side-view of GHC bout including the identified PH and MC period. The PHs and MCs were chosen to exactly match in terms of individuals, bodily positioning and activities (grooming) in order to identify the mechanisms by which GHC is initiated.

Figure 3.

Sunburst [47] showing behavioural sequences (n = 114) by the initiator (n = 25) leading to GHC. Starting behaviours are depicted in the inner coloured circle, with the grey outer circle being the endpoint of the sequence (i.e. GHC). In order to consider the full flexibility of all types of GHC initiations, we also included the three synchrony behaviours (nosewipe, self-scratch and torso). An interactive version is available as electronic supplementary material, figure S13.

Figure 4.

Probability of GHC initiation type in relation to (a) dyadic days of experience with GHC and (b) whether the dyad is a mother–offspring dyad or not. The lines in (a) and dots in (b) indicate the model fit of the multinomial model in table 2, with the shaded areas corresponding to the 95% credibility interval.