When chimpanzees share food with a friend or groom a pal, such favors are often exchanged over long periods of time within the context of a stable relationship.
“We studied the question in chimpanzees and bonobos—our two closest living relatives—and looked at the exchanges of grooming and food sharing, which are two common types of favors among these apes,” says Adrian Jaeggi, a postdoctoral researcher in anthropology at the University of California, Santa Barbara.
“They recognize others in the group, form long-term relationships, and associate with individuals who have helped them in the past,” he says.
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Photo credit: Jeroen Stevens