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Study Suggests Chimpanzees Exhibit ‘Contagious Urination’ Similar to Yawning

Observing a friend yawn might prompt you to yawn as well; this phenomenon called “contagious yawning” has been widely discussed in behavioral studies. Now, emerging research indicates that a similar behavior may occur in chimpanzees regarding urination. According to a new study, captive chimpanzees that witnessed their companions urinating were more inclined to follow suit.

The findings, which outline this behavior termed “socially contagious urination,” are detailed in a paper published in the journal Current Biology.

Primatologist Ena Onishi from Kyoto University first took notice of this behavior in 2019 while studying chimpanzees at the Kumamoto Sanctuary in Japan. She observed that multiple chimpanzees tended to urinate simultaneously, echoing certain human social behaviors, including the tendency for people to visit restrooms in groups.

Onishi explained that in Japan, there is even a term—Tsureshon—which describes the act of urinating in the company of others. This cultural insight, alongside an Italian saying implying that those who avoid urinating in groups have ulterior motives, sparked her curiosity to explore this behavior further.

To investigate, Onishi and her team recorded more than 600 hours of footage involving 20 chimpanzees, documenting 1,328 instances of urination. Their analysis confirmed that whenever one chimp urinated, it frequently triggered others to do the same.

Interestingly, the research highlighted specific patterns: lower-ranking chimpanzees were more likely to urinate after observing others, while being closer in physical proximity to the initial urinator significantly increased the chances of participation. However, the extent of social closeness—based on interactions like grooming—did not seem to affect this behavior, contrasting with studies on contagious yawning in humans where social bonds do play a role.

Given that humans tend to synchronize their restroom visits, the researchers speculate that this form of contagious urination could have deep evolutionary roots, possibly shared with a common ancestor. Chimpanzees, along with bonobos, are considered the closest relatives to humans.

According to co-author Shinya Yamamoto, this simultaneous urination could serve to enhance social bonding among chimpanzees, similar to humans’ collective behaviors. He noted, “Our findings indicate that both species exhibit behaviors influenced by social contexts, reinforcing bonds through seemingly mundane activities.”

While the current study focused solely on captive chimpanzees, the authors indicate that social urination likely occurs in wild populations as well. Future research may extend this investigation to wild chimps and other social animals.

Martin Surbeck, an evolutionary biologist at Harvard University not involved in the research, commented on the coordination seen in great apes, suggesting that group members often synchronize their actions in the wild.

The reasons behind the simultaneous urination among chimpanzees remain speculative. Researchers have proposed that such behavior could strengthen social relationships or serve as a strategic measure to mislead predators about the group’s movements.

Onishi highlighted the broader implications of their findings, stating, “Both humans and animals demonstrate myriad social behaviors that connect to group living. This research showcases how a fundamental act like urination can also become a socially influenced activity within a species.”

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