Hate waiting in line for the bathroom? Chimpanzees have a social solution: Go all at once.
A new study shows that peeing is contagious in chimpanzees, making it “the first study to investigate contagious urination in animals, including humans,” says Shinya Yamamoto, an animal behavior scientist at Kyoto University in Japan.
While observing a group of captive chimpanzees (Pan troglodytes), something caught the attention of Ena Onishi, who also studies animal behavior at Kyoto University. “I noticed a tendency for individuals to urinate at the same time,” she says. “This resemblance to certain human behaviors piqued my curiosity. In Japan, my home country, there is a specific term called ‘Tsureshon,’ which refers to the act of urinating in the company of others.”
Intrigued by this phenomenon, she wondered whether urination, like yawning and grooming, is contagious in chimps.
Onishi, Yamamoto and colleagues spent more than 600 hours studying 20 captive chimps living in a wildlife sanctuary — and observed them peeing more than 1,300 times.
An analysis of those observations revealed that chimps were likely to pee together, and if a chimp was near an individual that was urinating, it too was more likely to start peeing — suggesting that the behavior is contagious, the researchers report January 20 in Current Biology.
Unexpectedly, the team also found that this copycat behavior was not influenced by social closeness, as in the case of grooming and yawning. Instead, the researchers found that rank played a role. Low-ranking individuals were more likely than others to start peeing if a chimp nearby did. “This was an unexpected and fascinating result,” Onishi says. “It opens up multiple possibilities for interpretation.”
High-ranking individuals might influence the urination of others, Onishi says. Or perhaps low-ranking chimps “are more likely to notice and respond to the behaviors of others, including urination,” she says, given “their heightened vigilance in social settings.”
Further research could show if the phenomenon has any viable function, says Zanna Clay, a psychologist at Durham University in England who wasn’t involved in the research but who has studied the contagious nature of chimp grooming and play. “It’s a promising and preliminary step,” she says. “But I think … it’d have to be investigated in more detail to really understand if it’s something of relevance.”
Onishi and her colleagues next want to study other groups of chimpanzees, including wild chimps, to see “how social factors like sex, familiarity, and age might influence contagious urination.” And “expanding comparisons across species,” for example, by studying bonobos, Onishi says, “could provide especially intriguing insights when compared to our findings in chimpanzees.”