A recent study published on January 20 in the Cell Press journal Current Biology has introduced a concept that researchers call “contagious urinations.” This research, conducted with 20 captive chimpanzees at the Kumamoto Sanctuary in Japan, reveals that when one chimp urinates, others are more inclined to follow suit.
Ena Onishi from Kyoto University states, “In humans, urinating in the company of others can be seen as a social act.” “There’s an Italian saying that goes, ‘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), and in Japan, this behavior is known as ‘Tsureshon.’ Throughout history and across cultures, this act has been depicted in art and remains relevant in modern social settings. Our study indicates that this behavior may have ancient evolutionary origins. We discovered that chimpanzees, who are our closest relatives, often urinate in response to the urination of those around them.”
The researchers conducted this study after observing that the chimpanzees at the sanctuary often seemed to urinate simultaneously. This reminded them of human behavior and led them to consider whether it resembled contagious yawning. To investigate, they tracked urination behaviors over more than 600 hours, recording a total of 1,328 urination incidents. They analyzed the data to determine if the chimpanzees’ urinating was significantly synchronized and whether it was affected by the presence of others or by social dynamics.
The analysis revealed that urination events among the chimpanzees were notably more synchronized than would typically occur if they were simply urinating independently of one another. The study found that the probability of contagious urination increased as chimps were physically closer to the one that first urinated. Interestingly, those lower down the dominance hierarchy were more inclined to urinate when others did. This indicates that their urination behaviors may be shaped by social status, flowing from higher-ranking individuals to those of lower rank.
“We were taken aback to discover that social rank influenced the pattern of contagion,” Onishi comments. “Since there haven’t been any prior studies on contagious urination in any species, we likened it to contagious yawning, which is also a non-voluntary physiological action. Initially, we thought that social factors might resemble those seen in yawning, like stronger contagion between individuals who are socially close. However, our findings showed no indication of such social proximity effects. Instead, we noted a distinct impact of social rank, with those of lesser rank more likely to urinate when others did.”
Shinya Yamamoto, also from Kyoto University, adds, “This was an unexpected and intriguing outcome, as it opens up numerous avenues for interpretation. For example, it could indicate an underlying leadership role in synchronizing group behaviors, the strengthening of social ties, or a tendency for lower-ranking individuals to pay closer attention to their peers. These insights prompt interesting questions about the social significance of such behaviors.”
The researchers highlight that their findings could have crucial implications for understanding the role of contagiously urinating in promoting group cohesion, aiding coordination, or fortifying social connections. It sheds light on how this seemingly trivial and essential behavior might hold unrecognized social importance.
Further research is necessary to explore the specific functions and mechanisms behind contagious urination in chimpanzees. The researchers are also interested in discovering if this phenomenon occurs in other animal species.
