A new experiment has disproved the existence of a sense of justice in monkeys. In this respect informs German Center for Primatology.
For many years it was believed that only humans could experience complex emotions, including feelings of injustice. In order to perceive this concept, it is necessary to have a developed brain, to be able to compare oneself with relatives, and to determine the response of an action and its consequences (reward or punishment). In recent years, however, signs have begun to emerge that monkeys have a sense of justice. For example, a video of an animal throwing a cucumber prize at its trainer became popular because its relative received sweet grapes for completing a similar task.
New to work The behavior of cynomolgus monkeys showed that there is another explanation for such a response not related to advanced abstract thinking. The experiment was conducted according to four scenarios, but all had similarities: one of the monkeys had an apparently high-quality reward, but they received a bad reward for doing the job. In two scenarios, the reward was handed out by one person, in two scenarios by the automatic feeder, and in two scenarios by a relative and a monkey, while the relative always received a high-quality award. Four experiments made it possible to test combinations of all possible options.
It turns out that monkeys almost never refuse a bad reward given to them by an automatic feeder, but do so in more than 20% of experiments in which food is offered by an individual. This pattern of behavior is consistent with the frustration of a person who decides to give an animal a smaller reward than he can. Since monkeys are good at distinguishing between animate and inanimate objects, they cannot be disturbed by the sharer. The presence of a relative with a better reward had almost no effect on refusal to eat. But scientists have found strong gender differences – in 8% of cases women refuse bad food given by men in 42%.
Thus, the authors conclude that what was considered a “rebellion” against injustice in past experiments may actually be an act of resentment stemming from a person’s bad behavior. On the other hand, this conclusion will need to be confirmed by a number of other experiments, since such studies are very complex and require taking into account many small things.