If indeed our feelings, our morals and our ethics are the product of evolution, there must be traces of this evolution in the ancestors of humans and in animals more closely related to us. On the other hand, the identification of relatives and the memory of the "prisoner's dilemma played with others involve some minimum level of memory and analysis by individuals, which may explain why the notions of justice held by humans seem not to exist in simpler organisms. The study of notions of justice in animals is currently being developed, so it is premature to consider such studies as evidence of the evolutionary traces of morality and ethics, but they are still striking and encourage further research. One of the aspects studied in animals, related to our notion of justice, is the "aversion to inequity." Among humans, one of the concepts related to justice, equality, so there is an aversion to situations where there is no level playing field. This has been studied by sociologists, psychologists and economists, among them Ernst Fehr Swiss Fehr & Schmidt 1999, who tested the homo economicus model, used by orthodox economists, in which people simply want to maximize their profits, regardless of the inequality with respect to the earnings of others. Experiments with chimpanzees Brosnan 2004, capuchin monkeys van Wolkenten 2007 and dogs Range et al. 2008, suggest the presence of behaviors that reflect an aversion to inequity. In these experiments, the animals are rewarded, usually with food, in exchange for some object or some action (like giving the leg in case of dogs).
The rewards can be greater or lesser value for animals. In these experiments we have studied the reactions of animals to changes in the rewards for the same task. The result is that animals react very positive (and continue doing the work) for rewards of different values, provided that both receive the same reward. However, when a receive less reward than another, and both rewards are of considerable value, then the animal "discriminated" begins to behave in a negative way, leaving the task and even displaying aggression toward the experimenters. The evolutionary explanation behind these behaviors can be found in the fact that animals in a community where there is cooperative work, receive less reward than another animal that is usually involves doing work that others are benefiting, which is obviously disadvantageous from an evolutionary standpoint. From this we can assume that inequity aversion may not be present in species where there is cooperative work (hence the experiments now aim for social animals like apes, monkeys and dogs). As we see feelings as envy, humiliation, injustice, and behaviors against exploitation and inequality, may have their origin in the evolution of species.