For decades, the scientific community has wondered whether humans are the only creatures to feel a deep aversion to unfairness. Many studies argue this is not the case, based on the behaviour of certain animals such as capuchin monkeys or dogs, which seem to display instinctive jealousy when they feel wronged, particularly when sharing food or receiving attention.
Now a research team from the University of California, Berkeley is challenging this idea. The researchers analysed data from 23 studies, covering 18 animal species and over 60,000 observations. Applying a new method of analysis, they explored in-depth the notion of this aversion to unfairness.
Their research suggests that the behaviours observed in animals seem to be linked more to unmet expectations than to a real sense of injustice. “We can’t make the claim that animals experience jealousy based on this data. If there is an effect, it’s very weak and might show up in very specific settings. But it’s nothing like what we see in humans in terms of our deep-seated sense of fairness,” first author Oded Ritov explained.
This is because animal behaviour is frequently analysed through the lens of our own human perceptions, as evidenced by primatologist Frans De Waal’s well-known experiment. In it, two capuchin monkeys are placed side by side in glass cages. In turn, they are asked to hand over a token to a human researcher in exchange for a reward.
But for the same action, one receives a simple piece of cucumber, while the other is offered large sweet grapes. Faced with this “injustice”, the disadvantaged monkey loses his temper: he throws the cucumber away, bangs on the walls of his cage, and refuses to continue the exercise.
De Waal saw this as proof that aversion to unfairness is not restricted to humans. The authors of the present study, however, argue that the capuchin’s reaction has more to do with the frustration of not obtaining the coveted reward than with a feeling of jealousy towards the other monkey.
“We think that the rejections are a form of social protest. But what animals are protesting isn’t receiving less than someone else; rather, it seems like they’re protesting the human not treating them as well as they could,” Ritov posited.
Far from minimising the cognitive capacities of animals, these findings encourage us to reconsider human interpretations of their behaviour. Understanding these differences could deepen our understanding of the values that shape our own societies, while enriching our view of the animal kingdom.