The absence of reward induces inequity aversion in dogs

Friederike Range, Lisa Horn, Zsofia Viranyi, Ludwig Huber; 2009

One crucial element for the evolution of cooperation may be the sensitivity to others' efforts and pay-offs in comparison to one's own costs and gains. Inequity aversion is thought to be the driving force behind unselfish motivated punishment in humans, which constitutes a powerful device for the enforcement of cooperation.

Recent experimental research indicates that non-human primates also refuse to participate in cooperative problem solving tasks if they witnessed a conspecific obtain a more attractive reward for the same effort. However, little is known about non-primate species although inequity aversion may also be expected in other cooperative species.

Here, we investigated whether domestic dogs show sensitivity towards the inequity of rewards received for giving the paw to an experimenter on command in pairs of familiar dogs.

We found behavioral differences in dogs tested without food reward in the presence of a rewarded partner compared to both a baseline condition (both partners rewarded) and an asocial control situation (no reward, no partner), indicating that the presence of a rewarded partner matters. Our second experiment showed that it was not merely the presence of the second dog but rather the fact that the partner received the food and not the subject that was responsible for the change in the subjects' behaviour.

In contrast to the primate studies, dogs did not react to differences in the quality of food or effort. However, our results suggests that other species except primates may show at least a more primitive version of inequity aversion, which may be a precursor of a more sophisticated sensitivity to efforts and pay-offs of joint interactions.

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