Language is at the heart of what makes us human, but must have evolved from communication as occurs among today’s nonhuman primates. How and why this happened is one of the big unsolved puzzles of our time. Much research has compared our communication system with that of great apes, our closest living relatives, in order to identify the cognitive building blocks that shaped human language. Arguably the most powerful social tool in the animal kingdom, language may have evolved as an adaptation to a new demand: the coordination of joint action. Coordinated and cooperative joint action is only possible with effective communication, which in turn requires highly flexible adjustments to social context, interaction partner and ecological settings. Are the evolutionary roots of this plasticity to be found in the great ape (hominid) lineage? Despite evidence for signal invention and flexible signal combinations in great apes, this hypothesis remains to be tested, because most comparative work focuses on population- or species-level variation rather than variation at the individual level.
Our research group funded by a Freigeist Fellowship of the Volkswagen Foundation, awarded to Marlen in 2022, aims to address this important question. Over the next 5 (+3) years we aim to investigate the proximate factors driving communicative plasticity in great apes’ and humans’ social action coordination using a multimodal approach. To study sources of variation from the individual to the species level, we will apply a behavioural reaction norm approach (i.e. considering that individuals may differ in phenotypic plasticity for a given environmental condition) to extensive observational and experimental datasets on the communicative coordination of joint activities in wild and captive great apes (chimpanzees, orang-utans) as well as humans in large-scale, industrialized and small-scale, hunter-gatherer societies. By operating at the interface of comparative psychology, behavioural ecology and linguistics, this innovative comparative approach will help to draw critical inferences about the role communicative plasticity in joint action coordination played in the emergence of modern human communication.
