Familiarity affects other-regarding preferences in pet dogs

Other-regarding preferences are considered to be the foundation of human cooperation. However, the evolutionary origin of this behavior in humans remains poorly understood. So far, comparative studies in primates have led to mixed conclusions probably due to methodological differences relating to both task complexity and the types of control conditions used. Moreover, no clear link between phylogenetic relatedness and prosociality has been found, suggesting that other convergent selection pressures may play a role in the evolution of such behaviors. Here, using one of the cognitively less demanding tasks, we show for the first time, that dogs can behave pro-socially by donating food to a conspecific partner, but only if the partner is familiar. This highlights the importance of considering the social relationships between individuals when testing animals for other-regarding behaviors. Moreover, by including a social control condition, we show that the dogs' prosocial response was not due to a simple social facilitation effect. The current findings support recent proposals that other convergent selection pressures, such as dependence on cooperative activities, rather than genetic relatedness to humans, may shape a species' propensity for other-regarding behaviors.