“Chimpanzee Behavior: The Surprising Social Spread of Peeing Like Yawning!”

When you observe or hear someone yawn, you might suddenly feel compelled to mimic the action, thanks to a well-researched phenomenon referred to as “contagious yawning.” Now, fresh inquiries indicate that urination could operate similarly: Captive chimpanzees that witnessed their companions urinating were more inclined to do so themselves.

The scientists present their evidence for this “socially contagious urination” in a new paper published on Monday in the journal Current Biology.

Study co-author Ena Onishi, a primatologist at Kyoto University, became intrigued by chimpanzee urination in 2019. While observing captive chimpanzees at the Kumamoto Sanctuary in Kyoto, Japan, she noticed that the animals collectively tended to urinate simultaneously.

This observation reminded her of certain human actions—including contagious yawning and the propensity for individuals to go to restrooms in groups.

“In Japan, my native land, there exists a particular term known as ‘Tsureshon,’ which signifies the act of urinating in the presence of others,” Onishi explains to Science News’s Gennaro Tomma.

Besides Tsureshon, the researchers also refer to an Italian saying that states, “whoever does not urinate in company is either a thief or a spy.”

Consequently, Onishi opted to perform an experiment to uncover more details. She and her colleagues monitored the sanctuary’s 20 chimpanzees for over 600 hours, recording 1,328 “urination events” during their observation.

Upon evaluating the footage, the team validated their assumptions: When one chimp began urinating, others promptly followed.

Their data unearthed additional nuanced insights: For instance, chimpanzees of lower social ranks were more prone to urinate upon witnessing their peers doing so. The physical closeness to the initial urinator also heightened the probability that other chimps would imitate the action.

Social intimacy—or the bond strength between two chimpanzees determined by their time spent grooming or interacting—did not seem to affect the contagious urination. This contrasts with contagious yawning in humans, which does appear to be influenced by social closeness.

Given that humans are known to use restrooms together, the findings imply that contagious urination might possess a “profound evolutionary origin,” study co-author Shinya Yamamoto, also a primatologist at Kyoto University, conveys to Live Science’s Olivia Ferrari. This behavior may even trace back to a shared ancestor. (Chimpanzees, alongside bonobos, are humans’ closest living relatives.)

“In humans, we recognize that our choice to urinate is affected by social contexts that compel us to urinate concurrently with others, and this simultaneous urination could also foster further social bonding,” Yamamoto adds. “Our investigation involving chimpanzees clearly demonstrates that they share certain similarities in this behavior.”

Although the study exclusively involved captive chimpanzees, researchers suspect that contagious urination likely exists in the wild as well. Future investigations may examine the behavior among wild chimpanzees and other social species.

“If you traverse with great apes in their natural habitat, you often notice that group members really synchronize their actions,” remarks Martin Surbeck, an evolutionary biologist at Harvard University not involved with the study, to the New York Times’s Annie Roth.

Why do chimpanzees appear to urinate simultaneously? The study does not provide a conclusive answer, but the researchers have proposed several theories. Contagious urination might assist in reinforcing social bonds and enhancing group cohesiveness, or it could serve as a defensive tactic to obscure the group’s movements from potential predators.

“Humans and other animals share numerous social experiences linked to group living—we’re all impacted by the presence of others, even in routine activities,” Onishi informs Salon’s Matthew Rozsa. “For example, actions such as yawning, walking, rhythmic tapping, and even variations in pupil size are contagious in both humans and chimpanzees. Our research fits within this framework by demonstrating that urination, a seemingly straightforward physiological act, can also proliferate socially among a group.”