One persuasive hypothesis for the biological success of modern humans is that early hominids have undergone a major evolutionary transition from an individualistic, competitive nature to a group-oriented, cooperative social nature, which prepared the ground for the advent of language. Here, we are concerned with the evolutionary origins of one manifestation of human cooperativeness, the ‘interaction engine’, a set of capacities and motivations that produce hallmark outputs of human social interaction, including reciprocal signalling of understanding that performed actions are part of a larger joint activity, turn-taking with reciprocal roles and precision timing of individual acts, multimodal signals, and structuring of individual acts into sequentially organised chains and macro-level phases.
Previous research on the ability of great apes to engage in coordinated joint actions is controversial, with observational data on the one hand suggesting the existence of this ability and experimental data on the other hand painting a more skeptical picture. We advocate a closer analysis of natural behaviour using state-of-the art theoretical concepts and micro-analytical methods from the study of human social interaction to directly compare human and great ape social interaction. This project will thus investigate the capabilities for joint action in our closest relatives, the chimpanzees and bonobos, and compare them with human children. We will conduct observational studies on individuals engaged in naturally-occurring and ecologically relevant activities (apes: grooming, sex, chase-play; children: play and fight), focusing on the signals exchanged to coordinate entry, maintenance and exit from these joint actions. The interactions will be recorded while the focal individuals are in their own group (child-care facilities for human children), making the selection of co-operators for the joint activities an additional key component of the process and one that has been hardly studied in experimental settings. Observations of how human children spontaneously engage in joint activities like play or competitive activities like competing for toys will allow assessing how their way of entering, maintaining and exiting these activities develops and is affected by factors like the development of linguistic abilities, theory of mind and orientation towards social norms. This will also allow us to compare how the way great apes engage in joint actions resembles human cooperative joint actions (e.g., play) vs. competitive social interactions (e.g., fight).
Our results will shed light on the cognitive and communicative processes underlying joint actions in great apes and enable us to make direct comparisons with humans. The human ‘interaction engine’ is thought to be a pivotal precursor for the evolution of language and other uniquely human characteristics, suggesting that results will lead to better understanding of how natural selection has shaped key aspects of human uniqueness from ancestral primate roots.