The Grapes of Wrath

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Humans quickly notice unfairness and inequity. It’s no different with chimps and other primates.

Past studies have shown that chimpanzees and macaque monkeys display an aversion to inequity when given less-preferred food.

In one experiment, researchers grappled with angry reactions when they were handing macaques cucumbers and grapes: Because grapes were their preferred food, the macaques would fling the cucumbers at the researchers when they saw other monkeys getting grapes.

Now, a research team conducted a series of experiments where they determined that the monkey species displayed “social disappointment” toward humans, the Washington Post reported.

One experiment saw a subject monkey receive less-preferred food – fennel – from a human or an automated food dispenser. In another test, the subject animal received fennel while their simian partner in a nearby cage got grapes from a human or the machine.

The new findings showed that the subject would usually refuse the less-preferred food from the humans, but didn’t complain much when the machine did the same. This happened both when the primate was alone or with the partner monkey.

The team suggested that the monkeys figured out that the humans were intentionally giving them low-value food, while the machine is inanimate and “has no goal.”

“The monkeys have no social expectations of a vending machine and are therefore not disappointed,” said co-author Rowan Titchener.

Other researchers proposed that the disappointed behavior toward humans “suggests that this is a social response,” adding that the macaques seem to form “special expectations toward other social beings.”

Still, the authors cautioned that studying animal behavior has limitations and that scientists “need to avoid falling into the trap of viewing animal behavior without context, (solely) through a human lens.”