Chimps Steal Less Often From Their Friends, Even When Offered Pineapple

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Trilobites

The discovery may hint at the roots of human norms around fairness and friendship.

Yoyo, left, and Pasa, best friends living in the Ngamba Island Chimpanzee Sanctuary in Uganda. Chimp friendships are largely initiated by grooming.Credit...

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· 5:32 min

By Taylor Mitchell Brown

Oct. 23, 2026

Pasa and Yoyo, two female chimpanzees, are best friends. They spend their afternoons lounging together in the warm grass of the Ngamba Island Chimpanzee Sanctuary in Uganda, grooming and sharing food. Sometimes they even try to escape the grounds together.

They are also less likely to steal food from each other, according to the results of a new experiment that pitted friendship against pineapple slices.

The new study is the first to find that primates can prioritize friendships over tasty treats, revealing an ability to squash selfish impulses previously undocumented in our hairy ape cousins. The discovery, which may hint at the roots of human norms around friendship, was published in the journal Evolution and Human Behavior.

“It wasn’t obvious to us that chimpanzees would steal less from their friends,” said Oded Ritov, a social psychologist at the University of California, Berkeley and lead author of the study. The discovery shows that chimps, like humans, have social expectations of each other, he added. “We think that these expectations might be a basic building block that later evolved into fairness and other types of morality we see in humans.”

Notions of “friendship” in nonhuman primates have a contentious history. Many researchers have claimed that attributing the term to relationships in primates like chimps and bonobos is a kind of anthropomorphism, imposing ideas familiar to us onto distantly related animals, where they don’t belong.

“For a long time, it was like this F-word,” said Laura Lewis, a biological anthropologist at the University of California, Santa Barbara and coauthor of the study. But over the past few decades, primatologists have uncovered increasing evidence of friendships in social primates, finding that they show more trust and support toward the peers they feel close to.

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