Research has shown that some behaviors, like yawning, can be contagious. Now, a new study published in Current Biology has uncovered a peculiar social behavior in chimpanzees that experts call “contagious urination.”
The study, conducted with 20 captive chimpanzees at the Kumamoto Sanctuary in Japan, reveals that when one chimp urinates, nearby chimps are more likely to do the same—a phenomenon that may shed light on the social dynamics of our closest evolutionary relatives.
“In humans, urinating together can be seen as a social phenomenon,” Ena Onishi of Kyoto University said in a recent press release. “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),” says Onishi.
“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.”
Why Are Certain Behaviors Contagious?
Certain behaviors, such as yawning, laughter, and scratching, are known to be contagious across species. These phenomena result from evolutionary mechanisms enhancing social cohesion and group coordination. Contagious behaviors are often semi-voluntary and can be triggered by observing or sensing others performing the same action.
One prominent theory links contagious behaviors to mirror neurons—specialized brain cells that activate both when an individual performs an action and when they observe someone else performing it. Mirror neurons are believed to play a role in empathy and social bonding by enabling individuals to subconsciously “mirror” the emotions or actions of others.
From an evolutionary perspective, contagious behaviors likely serve practical purposes. For instance, contagious yawning has been proposed to help synchronize group sleep-wake cycles, which may enhance safety during vulnerable periods of rest.
To Pee or Not To Pee?
In this study, the researchers began investigating this behavior after noticing that chimpanzees at the sanctuary often appeared to urinate around the same time. Curious if this pattern resembled contagious yawning, they observed the chimps for over 600 hours, recording 1,328 urination events.
Their analysis revealed that urination was significantly synchronized, far more than random chance would predict. Proximity played a role; chimps close to an initial urinator were likelier to follow suit. The researchers also looked at the social connections between chimpanzees to see if that affected the contagiousness of urination.
“However, our results showed no evidence of effects related to social closeness,” Onishi said. “Instead, we observed a clear influence of social rank, with lower-ranking individuals being more likely to follow the urination of others.”
Social Hierarchy and Group Dynamics
The researchers suggest this behavior might be tied to group coordination or the reinforcement of social bonds.
Shinya Yamamoto, also of Kyoto University added in the press release. “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.”
Chimpanzee behavior has long been studied for insights into human social structures, and this finding offers a fresh perspective on how even seemingly mundane actions can play a role in group dynamics. The researchers believe that contagious urination may facilitate coordination or reinforce social bonds within the group, potentially serving as a subtle yet essential mechanism for group harmony.
Do Other Animals Experience Contagious Urination?
The researchers hope to explore whether this phenomenon occurs in other animals and to better understand its specific social functions.
As researchers continue to study this behavior, the findings may deepen our understanding of the evolutionary roots of social coordination in chimpanzees and perhaps in other species, including humans. For now, the study opens a new and intriguing avenue for exploring the complexities of social behavior in the animal kingdom.
Kenna Hughes-Castleberry is the Science Communicator at JILA (a world-leading physics research institute) and a science writer at The Debrief. Follow and connect with her on BlueSky or contact her via email at kenna@thedebrief.org