| From: Proceedings
of the National Academy of Sciences of the United States of America (PNAS)
. The absence of reward induces inequity aversion in dogs . By Friederike Range, Lisa Horn, Zsófia Viranyi, and Ludwig Huber. Communicated by Frans B. M. de Waal, Emory University, Atlanta, GA, October 30, 2008 (received for review July 21, 2008) . One crucial element for the evolution of cooperation may be the sensitivity to others' efforts and payoffs compared with one's own costs and gains. Inequity aversion is thought to be the driving force behind unselfish motivated punishment in humans constituting a powerful device for the enforcement of cooperation. Recent research indicates that non-human primates refuse to participate in cooperative problem-solving tasks if they witness a conspecific obtaining 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 toward the inequity of rewards received for giving the paw to an experimenter on command in pairs of dogs. We found differences in dogs tested without food reward in the presence of a rewarded partner compared with 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. Furthermore, we showed that it was not the presence of the second dog but the fact that the partner received the food that was responsible for the change in the subjects' behavior. In contrast to primate studies, dogs did not react to differences in the quality of food or effort. Our results suggest that species other than primates show at least a primitive version of inequity aversion, which may be a precursor of a more sophisticated sensitivity to efforts and payoffs of joint interactions. . Reaction: Inequity aversion in dogs has nothing to do with envy or jealousy, but with hierarchy. Contrary to humans, no dog is equal to the other. Either the other dog has a higher position, or it has a lower position (in the eye of the dog). Rewarding a dog with a higher position before rewarding the dog with a lower position, is considered normal in the dog world, also rewarding it more than the dog with a lower position is considered normal in the dog world. When humans fail to take notice of this hierarchy, or don't give the dogs involved the opportunity to establish such a hierarchy, the dog with the higher position (in the eye of the dog) will be frustrated. But it certainly isn't jealousy or envy, as was suggested in the NRC of December 10, 2008; it's a complete different emotion.  .
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