This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: In recent years, scientists have shown that chimpanzees favor certain peers by picking whom they prefer to groom and selectively sharing food. The behavior offers a glimpse into humanity's prosocial evolutionary past.
But a question has lingered: How might a chimpanzee friendship affect antisocial acts? In a new study that uses fruit as the loot, UC Berkeley researchers found that chimps steal less from their friends and that friendship status affected the emotional expression of both victims and thieves. Closely bonded chimps swiped pineapple pieces from one another less frequently than those with weaker relationships.
Additionally, victims were quicker to calm down when the thief was a friend, and thieves showed less hostility when stealing from a bonded pal than from a nonfriend. The new research deepens our understanding of the emotional underpinnings of our social lives, said Oded Ritov, the paper's first author and a Berkeley psychology Ph.D. student. "Collaborative relationships are important for our well-being, health and survival," said Ritov, who works with Berkeley's Social Origins Lab.
"Increasingly, we're understanding that this isn't something that's unique to us, but that other animals have friends as well." The paper is published in Evolution and Human Behavior. Scientists are sometimes hesitant to describe an apparently close relationship between chimps as akin to human friendship, arguing that we can't grasp their cognitive and emotional complexity. To identify those who showed signs of a close relationship, researchers observed 26 chimps for more than 800 hours at the Ngamba Island Chimpanzee Sanctuary in Uganda.
The team documented which chimps appeared to be closely bonded—like friends—by taking note of their grooming patterns, daily interactions and how regularly they were within arm's reach of others. Then they set up two rooms. One contained a "victim" chimp with three trays baited with pineapple.
Researchers attached a rope to the trays and led it into the other room, where a second chimp—the thief—could either leave the rope alone or yank it to steal the pineapple. Chimps stole in 70% of trials with nonfriends, compared with 61% of trials with friends. While nine percentage points may not seem large, each chimp experienced both friend and nonfriend conditions, a methodological technique that leads to a higher degree of confidence that the difference is meaningful and not just random chance.
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