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Humans’ dominance in the animal kingdom is increasingly challenged. Studies reveal that animals can craft intricate tools, exchange gifts with peers, and even interpret detailed medical scans. However, not all findings are positive. Certain negative human traits are mirrored in our animal counterparts. A recent study in Evolution and Human Behavior
Animals often display behaviors that might seem spiteful, but interpreting their motives is complex. For instance, a dog destroying your socks could have numerous underlying reasons, making it difficult to pinpoint spite as the cause.
To isolate spite as a motivator, researchers devised a specific experiment. “Humans are unique in their willingness to go out of their way to punish norm violators,” explained senior author Laurie Santos in a press release. “We penalize those who exploit resources unfairly or intend harm. This study explores whether such motivations are exclusive to humans.”
Capuchin monkeys (Cebus apella) are highly sensitive to the actions of their peers. Earlier studies on C. apella reveal that these monkeys are keenly aware of resource distribution fairness—particularly if another monkey receives a larger share. During group tasks, capuchins often avoid partnering with monkeys known for selfish or uncooperative behavior.
To conduct the study, researchers designed collapsible tables connected to long ropes. After allowing the monkeys time to grasp how the rope-table mechanism functioned, the team divided the capuchins into two categories: subjects and stooges.
In each trial, a stooge monkey was placed at the table while a subject monkey controlled the rope. High-value treats like Fruity Pebbles cereal (described by researchers as a “highly prized reward”) and marshmallow fluff were introduced, raising the stakes significantly.
The monkeys’ intentions were unmistakable. Repeatedly, subject monkeys pulled the rope to collapse the stooges’ table, causing the food to vanish. This occurred even when the stooges had done nothing to earn the food, demonstrating that the subjects punished them merely for receiving it.
“Our findings mark the first evidence of a non-human primate punishing others solely for having more,” lead author Kristin Leimgruber stated in the press release. “This ‘if I can’t have it, no one can’ behavior aligns with psychological spite, a trait once thought to be uniquely human.”
