Japanese study finds that chimpanzees urinate together
It's common for people to go to the bathroom at the same time as their friends or colleagues during breaks at school or during breaks at work. It has been revealed that chimpanzee groups also exhibit this social contagious urination, or 'co-urination.'
Socially contagious urination in chimpanzees: Current Biology
In chimpanzees, peeing is contagious | EurekAlert!
https://www.eurekalert.org/news-releases/1069719
Urinary contagion in chimpanzees: When a chimpanzee urinates, it's contagious to urinate too. Kyoto University Wildlife Research Center
https://www.wrc.kyoto-u.ac.jp/ja/publications/EnaOnishi/Onishi2025-cb.html
'In Italy there is a proverb that says, 'He who doesn't pee with his friends is either a thief or a spy,' and in Japanese the act of urinating with others is called 'toge-shone.' Such behaviors have been expressed in culture and art for centuries and continue to appear in modern social contexts,' says Ena Onishi, a doctoral student at Kyoto University's Wildlife Research Center.
In a paper published in the scientific journal Current Biology on January 20, 2025, a research group including Ohnishi and Associate Professor Shinya Yamamoto of the Kyoto University Institute for Advanced Study (currently Professor at the Institute for Future Human and Society) announced that 'contagious urination,' which is widespread in human society, also exists among chimpanzees, one of the species most closely related to humans.
The study involved more than 600 hours of observation time in 20 captive chimpanzees, including 16 males and 4 females, and recorded a total of 1,328 urinations during the study. The chimpanzees were divided into four groups, with a gender breakdown of 16 males and 4 females.
When the researchers compared a simulation (Simulation, see below) that assumed that chimpanzees' urination behavior occurs randomly with the observational data (Observation, see below), they found that the synchronization rate seen in the actual observations was higher than the simulation results. This suggests that the synchronization of chimpanzees' urination behavior is not a coincidence, but that some social factor is at work.
Furthermore, when they investigated the types of individuals who synchronized urination, they found that individuals closer to an individual that had urinated were more likely to urinate in succession, meaning that urination was 'contagious.' They also found that individuals with lower social ranks tended to urinate in succession to other individuals.
On the other hand, when an individual with a high social rank urinates, there is no tendency for other individuals to follow suit. In other words, individuals with a low social rank follow whoever urinated. In addition, there was no correlation between the level of social affinity, that is, how close the individuals are to each other and how frequently they groom each other, and the synchronization of urination.
'We were surprised to find that contagion patterns are influenced by social status,' said Ohnishi. 'There had been no previous research on contagious urination, so we initially expected that stronger contagion would occur between socially close pairs, like contagious yawning, a semi-spontaneous physiological behavior. However, we actually observed that contagion patterns were influenced by social status, not social closeness,' he said. 'Our research suggests that this phenomenon may have deep evolutionary roots.'
by Kumamoto Sanctuary
According to the researchers, possible reasons for synchronized urination behavior include coordinating group activity, communicating information through urination, or efficiently marking territory in a group.
'This is an unexpected and intriguing result that opens up a variety of possible interpretations, such as hidden leadership synchronizing group activity, strengthening social bonds, or attentional bias among subordinate individuals. These findings raise interesting questions about the social function of this behavior,' said Yamamoto.
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