Weeing is contagious in chimpanzees

Is it learned or ur-innate?
24 January 2025

Interview with 

Ena Onishi, Kyoto University

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Chimpanzees

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Researchers in Japan have discovered a chimpanzee’s toilet routine is copied by others. The phenomenon - called “contagious urinations” - has been described in the journal Current Biology. Here’s Ena Onishi at Kyoto University…

Ena - We studied contagious urination in captive chimpanzees. In Japan, where I'm from, there is a term called 'Tsureshon,' which basically means urinating in the company of others. And it seems like that is very widespread across cultures. So we developed research questions from those moments when we saw chimpanzees urinating together.

Chris - This is a bit like one person gets up and says, I'm off for a wee, and then someone else says, oh yeah, I'll come too. It's that sort of one person does it and then others follow suit.

Ena - We first thought of Tsureshon, which is exactly what you mentioned, but actually the behaviour itself is a lot more like contagious yawning, for example, when one urinates another follows, but we don't know if that was intentional or not.

Chris - Where did you do the observations? What animals were you watching?

Ena - We did observation in Kumamoto Sanctuary of Kyoto University where I'm based at and I observed 20 chimpanzees.

Chris - So do you think the fact that they're in an artificial setting might have influenced this or do you think this is a realistic representation of what is happening in the wild as well?

Ena - There are some limitations about the captivity. For example, our study group had four groups of five individuals. The group composition isn't exactly like what it is in the wild setting because it's a much, much smaller group obviously. But thinking that this behaviour of contagious urination isn't something learned or something strategic, we think it's more of a natural thing that can happen without any intentional purposes. So we are pretty sure that it happens in the wild as well.

Chris - What actually happens then? What were the observations? You get one chimp wees and then everyone piles in and joins in. Is that how it works?

Ena - Just me just watching chimpanzees and recording all the urination and I also recorded their instance proximity, like the distance between each other and analysed if the chimpanzees in close proximity were more likely to follow the urination.

Chris - Do they go to a place to urinate or does one of them have a wee wherever they're standing and anyone who can see them then copies? Or do they get together in a group of wee in one place,

Ena - Usually chimpanzees don't go for a specific location for the urination, but I do see a tendency that they don't want to wet themselves with urine, so they might change their position or they might move slightly so that they can go to the edge of something and then urinate from the top. But usually they just urinate wherever they are.

Chris - Chimpanzees a bit like us have a really important social structure and a hierarchy, don't they? They have one who tends to be in charge and then there are underlings. So does it matter who urinates first and therefore who copies who or does it spread from anyone who starts urinating and then everyone follows suit?

Ena - At least in our study, we did not find specific social traits of the initiator, but what we found is for lower ranking individuals, they were more likely to follow anyone's urination.

Chris - The big question then is why they do this. Now with yawning, which you've already mentioned, we hypothesise that this is all about staying awake and if you've got one person feeling sleepy and they yawn, it makes sense to make everyone yawn and arouse themselves so that no one falls asleep. Why would contagious weeing happen? Why do this?

Ena - Honestly, we don't have like a single answer to it, but there are a couple interesting possibilities that might be useful. One idea is it could be useful for state matching of the group and state matching is a term used for syncing up the internal states of individuals and if they can achieve this through contagious urination, it could promote our maybe shared readiness for collective movements or just share physiological alignments so that they make group activities much smoother. And another possibility is that it could be something that's similar to chameleon effects, for example, where copying someone else's behaviour helps strengthen social bonding. I don't have any data for it, but still we do think that it's more widespread. It's not just captive chimpanzee behaviour, but it can probably be seen in other apes as well, or even more primates or other mammals.

Chris - And I understand, you know it's a pretty big day for you in terms of submission of your thesis.

Ena - Oh yes. <laugh>, I just submitted mine and hopefully it goes well. This study is one of the main chapters of my thesis.

Chris - So hopefully with a paper in one of the world's best biology journals, you should be in a good position to get your PhD

Ena - <laugh>. Thank you so much.

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