Bonobos engage in joint commitment

Abstract

Joint action is central to human nature, enabling collectives to achieve goals otherwise unreachable by individuals. It is enabled by humans' capacity to understand and engage in joint commitments. Joint commitments are evidenced when partners in interrupted joint actions reengage one another. To date, there is no clear evidence whether nonhuman animals understand joint commitment, suggesting that only humans experience it. Here, we revisit this claim by interrupting bonobos engaged in social activities. Bonobos reliably resumed the activity, and the likelihood of resumption was higher for social compared to solitary activities. Furthermore, communicative efforts deployed to suspend and resume social activities varied depending on partners' social relationships and interactive roles. Our results suggest that bonobos, like humans, engage in joint commitment and have some awareness of the social consequences of breaking it.

Fig. 1. Resumption.

Variation of resumption probability according to nature of activity (A), social bond strength [dyadic sociality index (DSI)] (B), rank difference (C), interruption condition (D), and interaction roles (E to G). Plots depict the predicted probability of resumption for the marginal effects of the complete Bayesian models (A, model 1; B to D, model 2; E to G, model 3) and show how model predictions match the data. Upper/lower bars and ribbon edges depict 95% credible intervals (CrIs), and the mid-square or mid–ribbon lines represent estimated posterior means. Squares colored in blue represent estimated effects. Gray circles correspond to the proportion of resumption per dyad [A (social); B to D] or individual [A (solitary); E to G]. Larger circles indicate more observations.

Fig. 2. Communication for suspension.

Variation of communication probability at the time of suspension according to social bond strength (DSI) (A), rank difference (B), interruption condition (C), and interactional roles (D to F). Plots depict the predicted probability of suspension communication for the marginal effects of the complete Bayesian models (A to C, model 4; D to F, model 6) and show how model predictions fit the data. Upper/lower bars and ribbon edges depict 95% CrIs, and the mid-square or mid–ribbon lines represent estimated posterior means. Squares and ribbons colored in blue represent substantial effects. Gray circles correspond to the proportion of communication at the time of suspension per individual responsible for suspension (A to C) or any individual regardless of whether or not they were responsible for suspension (D to F). Larger circles indicate more observations.

Fig. 3. Communication for resumption.

Variation of communication probability at the time of resumption according to social bond strength (DSI) (A), rank difference (B), interruption condition (C), and interactional roles (D to F). Plots depict the predicted probability of resumption communication for the marginal effects of the complete Bayesian models (A to C, model 5; D to F, model 7) and show how model predictions match the data. Upper and lower bars and ribbon edges depict 95% CrIs, and the mid-square or mid–ribbon lines represent estimated posterior means. Squares and ribbons colored in blue represent substantial effects. Gray circles correspond to the proportion of communication at the time of resumption per individual responsible for resumption (A to C) or any individual regardless of whether or not they were responsible for resumption (D to F). Larger circles indicate more observations.