Urination, like sneezing, is 'contagious' in primates, including humans

Who knew that bathroom habits could reveal something profound about primate behavior? A recent study published in the journal Current Biology has uncovered an intriguing social phenomenon among chimpanzees – one that links social dynamics to urination.

The study has revealed a peculiar behavior among chimpanzees that researchers are now calling “contagious urination.”

The study, which was focused on 20 captive chimpanzees at the Kumamoto Sanctuary in Japan, revealed that when one chimp pees, others nearby are more likely to do the same.

Contagious urination in chimpanzees

“In humans, urinating together can be seen as a social phenomenon,” noted Ena Onishi of Kyoto University.

“An Italian proverb states, ‘Whoever doesn’t pee in company is either a thief or a spy’ (Chi non piscia in compagnia o è un ladro o è una spia), while in Japanese, the act of urinating with others is referred to as ‘Tsureshon’ (連れション),” she remarked.

“This behavior is represented in art across centuries and cultures and continues to appear in modern social contexts. Our research suggests that this phenomenon may have deep evolutionary roots. We found that chimpanzees, our closest relatives, tend to urinate in response to the urination of nearby individuals,” added Onishi.

This unexpected discovery highlights the social nature of what is usually considered a purely physiological behavior.

The researchers became curious about the possibility of synchronized urination after noticing that the chimpanzees often relieved themselves at the same time. They wondered whether this could be comparable to contagious yawning, a well-documented phenomenon in both humans and animals.

Synchronized urination in chimpanzees

To test their theory, researchers meticulously observed the chimpanzees for over 600 hours, documenting 1,328 urination events.

Their analysis confirmed that urination was significantly more synchronized than would be expected by chance. The likelihood of a chimpanzee urinating increased if they were in close physical proximity to another chimp who had just started peeing.

One of the most surprising findings was the role of social hierarchy in this behavior. Lower-ranking individuals were more likely to urinate after others, suggesting that peeing patterns are influenced by dominance structures within the group.

“We were surprised to discover that the contagion pattern was influenced by social rank,” Onishi explained.

“Since there were no prior studies on contagious urination in any species, we drew parallels to contagious yawning, another semi-voluntary physiological behavior. Based on this, we initially expected that any social influences might resemble those seen in yawning – such as stronger contagion between socially close pairs.

“However, our results showed no evidence of effects related to social closeness. Instead, we observed a clear influence of social rank, with lower-ranking individuals being more likely to follow the urination of others.”

Why does this happen?

The underlying reasons for contagious urination remain unclear, but researchers believe it could serve important social functions.

“This was an unexpected and fascinating result, as it opens up multiple possibilities for interpretation,” commented Shinya Yamamoto of Kyoto University.

“For instance, it could reflect hidden leadership in synchronizing group activities, the reinforcement of social bonds, or attention bias among lower-ranking individuals. These findings raise intriguing questions about the social functions of this behavior.”

If urination serves a social purpose in chimpanzees, it could play a role in maintaining group cohesion, facilitating coordination, or reinforcing social bonds – similar to how synchronized behaviors like grooming or yawning contribute to social structure in primates.

Do other animals do this?

This discovery opens the door for further research into contagious urination in species other than chimpanzees. Could similar patterns be found in other primates or even non-primate animals?

Understanding the social dynamics behind this behavior could shed new light on the evolution of group coordination and hierarchy in social animals.

For now, the study highlights that even the most mundane aspects of life – like peeing – can have surprising social significance. As research continues, we may find that synchronized bathroom breaks are not just a human quirk but a deeply rooted evolutionary behavior.

The study is published in the journal Current Biology.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–