Some theories postulate that human inequity aversion is at the basis of cooperation, as we compare costs and gains to decide whether it is convenient to collaborate with others. However, we are not the only species that is sensitive to inequity. Chimpanzees, capuchin monkeys, dogs, and rats also demonstrated to negatively react to unfair scenarios, i.e. unequal division of the resources within the group and/or violation of the own expectations. A bird species, the Eurasian jay, was shown to react to violation of expectations of hidden food content similar to humans. Jays allocated higher attentional resources to process negative events with respect to positive scenarios, which was more likely to be accepted. Interestingly negative reactions to the unfair outcome correlated with social rank, with more dominant subjects being more likely to reject the unequal pay and, vice-versa, less dominant subjects to accept it. Such correlation might be interpreted in terms of ecological relevance, considering that less dominant individuals have less access to the group resources and thus must accept less favorable situations. Interestingly, a similar pattern was reported in humans, showing that people with a high social rank have stronger negative reactions to cognitive illusions that violates their expectations.

All these studies support the idea of inequity aversion being a shared characteristic among animals, rather than a uniquely human feature. As such, it must have an ecological relevance, enabling the animal to only engage situations that are likely to tourn out advantageous for its survival.