Monkeys Hate Humans who are Mean to Other Humans

According to a new study, monkeys won't take food from people who treat other humans badly, showing that they tend to evaluate humans based on social behavior. The study provides evidence that humans aren't the only animals that judge on the basis of third-party interactions.

An earlier study by Hamlin et al, also published by Nature, had found that 6- to 10-month-old babies tend to trust people who are helpful to others and dislike people who are mean toward others. This ability to know who can be a better friend and foe forms the basis of our social interaction with others. A study by Damian Scarf et al published in PLOS ONE has cast doubt over Hamlin's study.

In the present study, researchers placed capuchin monkeys in front of people who were either shown to be helpful toward others or those who were rude. Monkeys were then given food by the "good" and the "bad" people. Researchers found that monkeys rejected food from people who refused to help other people in need, while they accepted food from helpful people. Researchers say that the experiment shows how monkeys posses the ability of evaluating people based on third-party interactions.

"We find that the monkeys accept food less frequently from those who persistently reject another's requests for help. This negative social evaluation effect is robust across conditions, and tightly linked to explicit refusal to help. Evaluation of potential helpfulness based on third-party interactions may thus not be unique to humans," the researchers wrote.

The study can be found at Nature Communications.