Chimpanzees avoid stealing from close associates

Chimpanzees are less likely to steal food from individuals they are close to, according to a study published in late September 2026 in the journal Evolution and Human Behavior. Researchers observed this behavior in 26 chimpanzees at a sanctuary on Ngamba Island in Uganda.

Study lasted over 800 hours

The study involved observing the chimpanzees for more than 800 hours, tracking interactions such as grooming and proximity. Researchers also recorded which chimpanzees were willing to pull a rope to steal food from others.

Stealing rate differs by relationship

Chimpanzees pulled the rope in 70% of trials when facing a non-friend, but only 61% of the time when facing a close associate. The study tested each animal in both scenarios, reducing the possibility that the results were due to chance.

Victims react but calm faster with close associates

When a close associate stole food, the victim initially showed strong anger, such as stamping and crying, but calmed down more quickly than when a distant chimpanzee stole food. This suggests that close relationships may influence emotional responses.

Thieves show different signals based on relationship

The behavior of the thieves also changed depending on the relationship. Negative signals, such as aggression, faded more quickly when stealing from a close associate, indicating a possible awareness of the relationship.

Researchers see antisocial restraint in chimpanzees

Oded Ritov, one of the researchers, called this the first evidence of antisocial restraint among bonded great apes. This suggests that chimpanzees may have a sense of preferential treatment for close associates, similar to human friendships.

Human-like expectations in non-human primates

Jan Engelmann, an associate professor of psychology, noted that non-human primates already show partner-specific intentions. Human friendships add an expectation, as people expect more from close associates. These expectations might be the foundation of today’s moral principles.

Study limited to sanctuary chimpanzees

The study only involved chimpanzees in a sanctuary, where they are used to humans and fed regularly. There is no evidence that wild chimpanzees would behave the same way, as their environment and food availability differ.

Future research on cooperation beyond friendship

The researchers now aim to investigate whether these expectations extend to cooperation with individuals who are not close friends, potentially expanding the understanding of social behavior in chimpanzees.