Imma Perfetto
Cosmos science journalist
After noticing that 20 captive chimpanzees at Kumamoto Sanctuary, Japan, appeared to urinate at about the same time, a team of researchers decided to spy on their toilet habits… for science.
Just as a sleepy individual can set off a whole round of synchronised yawns in humans, we now know that when one chimpanzee pees, others are more likely to follow.
The bizarre behaviour seems to be influenced by social hierarchy, with a tendency to flow down from more dominant to less dominant individuals.
This is the first time the phenomenon, which researchers have coined “contagious urinations”, has been described.
“Since there were no prior studies on contagious urination in any species, we drew parallels to contagious yawning, another semi-voluntary physiological behaviour,” says Ena Onishi of Kyoto University’s Wildlife Research Centre, lead author of the new Current Biology study.
“Based on this, we initially expected that any social influences might resemble those seen in yawning – such as stronger contagion between socially close pairs. However, our results showed no evidence of effects related to social closeness.
“Instead, we observed a clear influence of social rank, with lower-ranking individuals being more likely to follow the urination of others.”
The team analysed more than 600 hours of footage to determine the chimps synchronised their urinations, rather than simply peeing at random times with respect to one another.
According to Shinya Yamamoto, also of Kyoto University, the findings raise intriguing questions about the social functions of this behaviour.
“For instance, it could reflect hidden leadership in synchronising group activities, the reinforcement of social bonds, or attention bias among lower-ranking individuals.”
The researchers say more research is needed to understand the specific functions and mechanisms underlying contagious urination in chimpanzees. They’re also curious to know whether this phenomenon exists in other species.
