26.04.2022 Marlen Fröhlich

Human language requires exceptional behavioural plasticity, given that effective communication in joint action contexts relies on highly flexible adjustments to social contexts, interaction partners and ecological settings. Thus, whether nonhuman species can change their communicative behaviour in response to the immediate (“behavioural flexibility”) and developmental environment (“ontogenetic plasticity”) has critical implications for communicative innovativeness prior to the emergence of human language, with its unparalleled productivity. Here, we used a comparative sample of wild and zoo-housed orang-utans of two species (Pongo abelii, P. pygmaeus) to assess wild-captive contrasts in two parameters of communicative plasticity: gestural repertoires (i.e. sets of gesture types) and redoings (i.e. gestural repetition and elaboration after communicative failure). In a first study, we found that repertoires on both the individual and population level are larger in captive than wild settings, regardless of species, age class or sampling effort. In a second study, we examined the production and effectiveness of gestural redoings, and identified wild-captive contrasts in Bornean orang-utans, but not the Sumatrans (i.e. the more sociable species). We thus conclude that orang-utans exposed to more sociable and terrestrial conditions evince remarkable behavioural plasticity, in that they produce additional innate or innovated signals, as well as more elaborate communicative repair strategies. These findings may suggest a latent capacity for innovativeness in these apes’ communicative systems, which is backed up by preliminary evidence for geographic variation in the use of vocalizations and gestures. A future large-scale project that systematically maps differences in repertoire and functional use across study sites may advance research on the precursors of productivity in unprecedented ways.