Dogs re-engage human partners when joint social play is interrupted: a behavioural signature of shared intentionality?

Hypotheses regarding the evolution of uniquely human social cognition often emphasize not only mental state representation, but also mental state sharing. Mental state sharing is evident in instances of joint intentionality – mutual understanding between individuals of each other's simultaneous and interdependent commitment to a shared activity or goal. Comparative studies supporting the human uniqueness of joint intentionality show that, as compared to human children, chimpanzees, Pan troglodytes, who engage with humans as cooperative partners do not altruistically help others achieve their goals across the same range of contexts, do not attempt to re-engage cooperative partners in problem-solving or social games at the same rate and do not show spontaneous role reversal. Although recent work supports the possibility that bonobos, Pan paniscus, may re-engage conspecific partners after interrupted social grooming, the extent to which other animals show similar behaviour across more diverse contexts remains largely unexplored. Domestic dogs', Canis familiaris, propensity to interact with humans in cooperative contexts makes them a potentially promising comparative model of prosocial mental state sharing. Here, we investigated a behavioural signature of joint intentionality during social play between humans and dogs (N = 82). Our results present the first experimental evidence of re-engagement behaviour in dogs, as dogs preferentially attempted to reinitiate an interrupted social game with their previous partner relative to a passive bystander. These findings suggest that dogs exhibit a key marker of joint intentionality and open the door for future research on the cognitive mechanisms supporting this behaviour.