go with the flow Peeing is contagious among chimps Physical proximity, social dominance are primary factors involved in "contagious urination" behavior. Jennifer Ouellette Jan 20, 2025 11:00 am | 5 "Well, if you're gonna pee, I might as well too." Credit: Onishi et al., 2025/CC BY-SA "Well, if you're gonna pee, I might as well too." Credit: Onishi et al., 2025/CC BY-SA Story textSizeSmallStandardLargeWidth *StandardWideLinksStandardOrange* Subscribers only Learn moreWhen ya gotta go, ya gotta go, and if it sometimes seems like the urge to pee seems more pressing when others nearby are letting loosewell, there's now a bit of science to back that up. It turns out that humans may not be the only species to experience "contagious urination," according to a new paper published in the journal Current Biology. Chimpanzees living at the Kumamoto Sanctuary in Japan are also more likely to relieve themselves when others are doing so nearby, and the behavior seems to be hierarchical, "flowing down" from dominant chimps to more passive ones.In humans, urinating together can be seen as a social phenomenon, said coauthor Ena Onishi of Kyoto University. An Italian proverb states, Whoever doesnt pee in company is either a thief or a spy (Chi non piscia in compagnia o un ladro o una spia), while in Japanese, the act of urinating with others is referred to as 'Tsureshon' (). 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.Onishi, et al decided to study the phenomenon after noticing that many chimps in the sanctuary seemed to synchronize when they peed, and they wondered whether the phenomenon might be similar to how one person yawning can trigger others to follow suitanother "semi-voluntary physiological behavior." There had been no prior research into contagious peeing. So they filmed the 20 captive chimps over 600 hours, documenting over 1,300 "urination events."Those results supported the initial hypothesis that chimps tended to urinate in sync rather than randomly. Further analysis showed that the closer a chimp was to another peeing chimp, the more likely the probability of that chimp peeing as wellevidence of social contagion. Finally, Onishi et al. wanted to explore whether social relationships (like socially close pairs, evidenced by mutual grooming and similar behaviors) influenced contagious urination. The only social factor that proved relevant was dominance, with less-dominant chimps being more prone to contagious urination.There may still be other factors influencing the behavior, and more experimental research is needed on potential sensory cues and social triggers in order to identify possible underlying mechanisms for the phenomenon. Furthermore, this study was conducted with a captive chimp population; to better understand potential evolutionary roots, there should be research on wild chimp populations, looking at possible links between contagious urination and factors like ranging patterns, territory use, and so forth.This was an unexpected and fascinating result, as it opens up multiple possibilities for interpretation, said coauthor Shinya Yamamoto, also 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.DOI: Current Biology, 2025. 10.1016/j.cub.2024.11.052 (About DOIs).Jennifer OuelletteSenior WriterJennifer OuelletteSenior Writer Jennifer is a senior writer at Ars Technica with a particular focus on where science meets culture, covering everything from physics and related interdisciplinary topics to her favorite films and TV series. Jennifer lives in Baltimore with her spouse, physicist Sean M. Carroll, and their two cats, Ariel and Caliban. 5 Comments