Giving Up Pineapple for a Best Friend... Chimps Also Take Less Food from Friends

More Willing to Forgive Friends Who Take Their Food

A study has found that chimpanzees are less likely to take food from close friends, even when they have the chance to get a favored treat.

Chimpanzees welcome a birthday cake at a zoo in Spain. EPA-Yonhap News Agency

According to The New York Times (NYT), researchers at the University of California, Berkeley, reported the results of an experiment conducted at the Ngamba Island Chimpanzee Sanctuary in Uganda in a paper published in the journal Evolution and Human Behavior on October 23 (local time).

The researchers first analyzed about 800 hours of video to assess the closeness of relationships among 26 chimpanzees. They recorded behaviors such as grooming and everyday interactions, then selected chimpanzees who appeared to have close, friend-like bonds. They then paired the chimpanzees and placed each one in a separate room, side by side. Each pair could consist of close friends or companions who were not particularly close.

In one room, the researchers placed a metal tray holding pieces of pineapple. In the other, they set up a rope connected to the tray. If the chimpanzee in the room with the rope pulled it, it could draw the pineapple in front of the chimpanzee in the neighboring room toward itself and take it.

The experiment found that the chimpanzees took the food in 70% of trials when paired with a companion they were not close to. But when paired with a friend, the rate fell to 61%. When a female chimpanzee named Yoyo was given the chance to take food from her close friend Fasa, she did not pull the rope and even refused to take part in the experiment.

Even more interesting was how the chimpanzees whose food was taken reacted. Each chimpanzee experienced both a situation involving a friend and one involving a chimpanzee who was not a friend. When a friend took their pineapple, the chimpanzees showed strong displeasure and anxiety, pounding the ground with their fists, shouting loudly, and scratching themselves as if uneasy. In later trials, however, they were more accepting when the same friend repeated the behavior.

When the other chimpanzee was a companion they were not close to, they showed a similar level of anger throughout the experiment. The researchers said this suggested that they viewed the situation as more hostile.

Oded Litov, a professor in UC Berkeley's Department of Social Psychology who led the study, said, "These expectations may be a basic element that later developed into fairness and various moral concepts in humans." Jan Engelmann, a senior researcher at the Institute of Social Origins and a co-author of the paper, said, "These findings deepen our understanding of the evolutionary roots of friendship."

Whether relationships among primates can be considered "friendship" has long been debated in academic circles. Many researchers have criticized applying the concept of "friendship" to primate relationships as mere "anthropomorphism"—the projection of human emotions and values onto animal behavior. Others argue that research over the past several decades has continued to find evidence that primates show greater trust and support toward individuals they feel close to.

In fact, close chimpanzees spend time together, hold hands and sleep alongside one another. They also protect each other when fights break out and comfort one another when one is grieving. They may even show jealousy when they see a friend grooming another chimpanzee, and try to prevent the two from growing closer.

This content was produced with the assistance of AI translation services.