Psychologists investigated whether animals are capable of feeling envy.

Researchers have repeatedly conducted experiments to determine the reasons behind animal behavior in various situations and whether they can experience "human-like" emotions. For instance, the authors of recent studies discovered which side dogs take in domestic disputes and also suggested that dogs may indeed be capable of jealousy.

Specialists from the University of Berkeley in the USA performed a meta-analysis of 23 studies, analyzing data from over 60,000 observations of 18 animal species. All the studies examined addressed the phenomenon of unfairness aversion, which in humans can manifest as envy. The results of the "largest empirical study to date on unfairness aversion in non-human species" were published in the scientific journal Proceedings of the Royal Society B.

In recent years, evolutionary psychologists have noted that animals ranging from crows to capuchin monkeys tend to react to unfairness, such as being denied a treat or seeing it go to someone else. Their behavior in such situations is often compared to human envy. The authors of the new article re-examined existing research data, modified their analysis methods, and concluded that humans may be unique in their aversion to unfairness.

Firstly, the results of many of the studies reviewed were based on data from small sample sizes, making it difficult for them to be replicated with other animals. Secondly, the new analysis indicated that animals during the experiments might not have experienced envy, frustration, or indignation due to unfairness at all.

When monkeys were denied a treat after several experiments in which they had received it, they might have felt disappointment. The animal did not necessarily envy other monkeys who received the treat; indignation arose even if the desired food was in an empty cage and did not belong to any supposed "rival."

"Animals protest not because they receive less than anyone else. Rather, they protest against the fact that humans do not treat them as well as they could," the study authors explained.

According to the researchers, what their predecessors interpreted as envy may not correlate with unfairness aversion. There is reason to believe that the animals involved in the experiments reacted to unmet expectations. This trait is common to both humans and other biological species.