A cute dog playing in the grass. Stefan Stefancik

Your dog might know whether or not you’re a good person. Researchers found monkeys and dogs negatively evaluate people who are not nice to others, a study published in the journal ScienceDirect said, according to New Scientist .

The study found capuchin monkeys negatively evaluate people who refuse to help others and individuals who exchange unfairly with others. Researchers also found dogs negatively evaluate people who refuse to help their owners.

Monkeys and Food Offers

Researchers tested whether capuchin monkeys would show preference for humans who help others by having the monkeys watch an actor struggle to open a container with a toy inside. The actor then showed the container to a second actor who would either help or refuse to aid the first actor. After that, the monkeys were each offered food and had to choose which offer to take.

Researchers found the monkey showed no preference between accepting food from the two actors when the actor helped the other. However, when one of the actors refused to aid the companion, the monkey more often took the food offer from the the struggler.

Monkeys and Ball Playing

Researchers also looked into monkeys’ attitude to fairness. For the analysis, two actors had three balls each. Actor A requested balls from actor B, who turned over the three balls. Then actor B requested the balls from A, who then either gave the three balls back or didn’t at all. The actors then offered the monkeys a reward.

Again, the monkeys showed no preference when the companions were nice to each other. However, the monkeys chose actor B when actor A didn’t return the balls, meaning the animals, again, chose the struggler more often.

Dogs and Ball Playing

When it comes to dogs, researchers tested whether canines preferred individuals who helped their owner. Similar to the test involving monkeys, each owner tried to open a container. The owner then presented it to one of two actors who either helped or refused to aid the companion. The actors then offered a reward to the dog between them. One actor either helped or refused to, while the other individual was passive.

Like monkeys, the dogs had no preference when the actor helped the owner, but were more likely to choose the passive actor if the first one had refused to help.

Here’s a video of the dog experiment:

Scientists think the animals end up with an emotional reaction when they see someone behaving antisocially, said James R. Anderson, one of the authors of the study according to New Scientist . The study was conducted by a team at Japan’s Kyoto University.