It’s a well-known fact that yawning is contagious and can spread around a room in a matter of seconds.
Now, a study has shown that the same is true – for peeing.
Researchers from Kyoto University found that chimpanzees are more likely to urinate when they see others doing it.
Ena Onishi, who led the study, said: ‘In humans, urinating together can be seen as a social phenomenon.
‘An Italian proverb states, “Whoever doesn’t pee in company is either a thief or a spy”, while in Japanese, the act of urinating with others is referred to as “Tsureshon”.
‘This behaviour 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.
‘We found that chimpanzees, our closest relatives, tend to urinate in response to the urination of nearby individuals.’
It’s a well-known fact that yawning is contagious and can spread around a room in a matter of seconds. Now, a study has shown that the same is true – for peeing
The researchers decided to investigate after noticing that captive chimpanzees living at the Kumamoto Sanctuary in Japan tended to urinate at about the same time.
The behaviour reminded them of people, and so they trawled through more than 600 hours of video footage of the chimps, analysing 1,328 times the animals went to the toilet.
The results showed urination events were significantly more synchronised than they would be if the primates were just peeing randomly.
The closer a chimp was to someone who has just urinated, the more likely they were to do the same thing.
That was based on analysis of urinating chimpanzees who were within arm’s reach of each other, within three metres (10 feet) of each other, or further than three metres away.
While contagious urination is thought to happen in human beings, it hasn’t been scientifically investigated.
The new study, in one of our closest relatives, found chimps who have less social status are more likely to copy someone else who has just urinated.
That might be because those lower down the hierarchy are keeping a closer eye on more respected chimpanzees, or because they are more stressed due to their poor ranking in chimp society.
The new study, in one of our closest relatives, found chimps who have less social status are more likely to copy someone else who has just urinated
Ms Onishi said: ‘Since there were no prior studies on contagious urination in any species, we drew parallels to contagious yawning, another semi-voluntary physiological behavior.
‘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 authors of the study, published in the journal Current Biology, say there may be tendency for urination behaviour to ‘flow down’ the dominance structure in chimpanzee groups.
They also suggest urination, as well as being used to scent-mark territory, could be something chimpanzees do before a long-distance trip as a group – rather like people.
Dr Shinya Yamamoto, senior author of the study, also from Kyoto University, described the urination behaviour of lower-ranking chimpanzees as ‘unexpected and fascinating’.
He said: ‘It could reflect hidden leadership in synchronising 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 behaviour.’
Experts are also curious to know whether this phenomenon exists in other species.
