We humans have a strong sense of justice. Various experiments suggest that some animals, including monkeys, wolves, and crows, may look alike. But their sense of fairness appears to be very different from ours, a recent study shows. Accordingly, the apes experience a mixture of social disillusionment and competition for food rather than injustice in the human sense.
If we feel unfairly treated, when distributing snacks for example, we usually make it very clear. We complain or dispense with the dry biscuit stick if our counterpart gets a piece of cream cake instead. Similar behavior has often been observed in animals in experiments. If a given animal receives a better reward for the same performance, the experimental animal will often give up its reward “in protest”. But does this really mean that animals can feel unfairly treated compared to their peers?
Unsatisfactory leverage tricks
To find out, researchers led by Rowan Teichner of the German Primate Center in Göttingen conducted various behavioral experiments with Sinomolgus monkeys. The basic principle: the animals had to pull a lever and be rewarded with lower quality feed. High-quality rewards were also apparent, but they were out of reach for the monkeys. The experimental setup can vary in two places. The inferior food either came from a vending machine or was given to the monkeys by a human trainer. In addition, the animals were either alone or in sight of a partner who was rewarded with high-quality food for the crane trick.
Titchener’s team observed how the monkeys reacted to the situation — whether they rejected inferior food when they saw their peers get better rewards. In this way, the researchers were able to test three common hypotheses that are supposed to explain the animal’s apparent sense of justice in the earlier experiments. The first is that animals reject inferior food because they feel they are being treated unfairly in a human sense and they protest. The second assumes that the animals expected better food and therefore rejected the worse. The third hypothesis is based on social disillusionment. The animals feel “cheated” by their trainer because they are better used to eating snacks than him.
A different sense of justice than ours
The result: When the lowest reward came from the machine, the cynomolgus monkeys never rejected it. However, when a trainer handed them food, they refused it more than 20 percent of the time. From this, Titchener and her colleagues inferred that the monkeys were disappointed in their trainer because he made a conscious decision to give them an inferior reward. “Monkeys do not have social expectations for a machine, and therefore they are not disappointed,” Titchener explains. According to the researchers, the monkeys’ behavior can be best explained by the third hypothesis, which is social disappointment.
According to the scientists, a certain degree of competition for food also plays a role. Because once a certain type of food was present, the monkeys grabbed the reward faster on average, even if it wasn’t objectively the tastiest snack. The results of the study confirm that monkeys also have a sense of justice, but this apparently differs from the typical human sense of justice.
Source: Deutsches Primatenzentrum GmbH – Leibniz Institute for Primate Research; Specialized article: Royal Society for Open Science, doi: 10.1098/rsos.221225
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