Peeing With Your Peers

Kyoto University

Kyoto, Japan -- Italian, it has been said, has a proverb for anything.

Chi non piscia in compagnia o è un ladro o è una spia -- "Whoever doesn't pee in the company of others is either a thief or a spy" -- goes one such saying, describing a communal act that in Japanese is known as tsuré-shon.

Social urination can be found represented in artwork across the centuries and around the world, and even today continues to be represented in cultural tropes. Now, researchers in Japan -- observing chimpanzees -- are suggesting that this phenomenon has evolutionary roots even deeper than previously expected.

Despite decades of research into other contagious behaviors such as yawning, contagious urination has never been studied scientifically in any species. To tackle this, a team at Kyoto University conducted 604 hours of direct observation at the University's Kumamoto Sanctuary, documenting 1,328 urination events. The researchers analyzed whether these were aligned in time, triggered by nearby individuals, or influenced by social relationships.

The team's findings, published in the journal Current Biology, reveal clear evidence for contagious urination. Events were synchronized in observation more than in computer simulations with randomized timing. Additionally, the closer chimpanzees were to a urinator, the more likely they were to follow. Further, individuals with lower social rank showed higher rates of 'contagion', suggesting that the behavior tends to flow down the dominance hierarchy.

"This is the first study to show that urination behavior in animals can be socially contagious," says lead author Ena Onishi, suggesting that, what appears to be a simple physiological act may actually serve more complex social purposes.

"For instance," continues Onishi, "our findings show a possible link between contagion patterns and social status, suggesting that further investigation could shed light on the evolutionary functions of this phenomenon, such as hidden leadership in synchronizing group activities or reinforcing social bonds."

Moreover, say the researchers, their study not only resonates with human behaviors -- such as group restroom use -- but also raises the possibility that this phenomenon could be more widespread across species, reflecting universal principles of group coordination.

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