The influence of social dynamics on the gestural communication of East African chimpanzees

Abstract

Great apes use gestural communication flexibly and intentionally to request a range of goals across diverse social contexts. The cognitive capacities required for this communication system have been compared to those underlying human language, leading some to suggest a gestural origin to linguistic communication. Both human language and great ape gesture have evolved within rich social systems. Humans adjust their use of language to specific social situations – accommodating to specific recipients or conforming to local dialects. However, the influences of social dynamics on great ape gestural communication remain highly understudied. To address this gap, I explore how individual identity, the relationship between signaller and recipient, and community membership impacts the use of specific gesture units, gesture expression, and the timing of communication across five communities of wild East African chimpanzees (Pan troglodytes schweinfurthii).

The overall structure of gestural interactions – the timing between signal and response – and the broad repertoire of gesture units was consistent across communities, suggesting that chimpanzees inherit the broad strokes of their communication as a species-typical system. Nevertheless, chimpanzees also conform to community specific preferences for regularly used gesture units and in the expression of specific gesture shapes. Signallers used different gesture units and gesture shapes depending on their social relationship to the recipient – most notably their kinship and sex relationships. Recipients also adjusted their latency to respond to specific signallers, responding faster to individuals with whom they shared weaker (less predictable) social bonds. Like humans, chimpanzees appear to conform to local dialects and adjust their gesture communication to accommodate specific communicative partners. These findings reveal previously hidden layers of social cognition used by chimpanzees during gestural communication; the decisions they make, and the distinct roles that signallers and recipients play when entering a gestural interaction.