The gestural communication of mountain gorillas (Gorilla beringei beringei)

Abstract

Gestures are communicative tools with which great apes navigate close-range social interaction. Sharing key commonalities with human linguistic behaviour, the ape gestural system has long been discussed as a potential precursor to language. While gesture studies have increasingly included data on natural wild-type ape behaviour, the role gestures play in wild gorilla sociality remains largely unexplored.

I studied four social units of mountain gorillas living in the Bwindi Impenetrable National Park, Uganda, and collected ad libitum video data on daily social interactions across age classes (157 observation days, 53 individuals). Using a novel ELAN-based bottom-up framework for the systematic study of ape gesture (GesturalOrigins), I coded 3330 intentionally produced gesture instances. Mountain gorillas employed 63 gesture actions, ~75% of which were shared with other ape species. Applying latent class analysis, these were split into 126 finer-grained units (‘morphs’). Mountain gorillas requested 11 basic goals, and gesture actions showed high overlap in function with the use of gesture by Pan. Gorilla-specific units were primarily used in requests for sexual and (to an extent) affiliative interaction, and sexual solicitations were associated with the highest gesturing effort and the greatest diversity of synonymous gesture units (followed by play initiations). Play was mostly requested through audible gestures, while gesturing for sex and grooming was biased towards visual forms. In comparison to East African chimpanzees, mountain gorillas gestured more frequently from the ground, from closer proximity, and employed more contact and fewer audible gestures. Despite mountain gorillas’ smaller sized groups and less cooperative nature compared to Pan, they gesture as frequently, with a repertoire of similar size, and employ gestures for similar goals. Investigating wild gorilla gesture use contributes not only a better understanding of gorilla communication but crucial context for theories on the ancestral state of human communicative behaviour and the evolution of language.