When nature calls: a study’s findings on contagious chimp urination

Nature is filled with synchronized tunes: the melodic songs of birds, croaks of frogs, and bladders of urgent chimps. As chimpanzees urinate, a new study reveals that surrounding chimps may join in synchronized streams. Scientists now hypothesize that this contagious urination could shine insights on social dimensions and behaviors beyond the chimpanzee species.

This past January, researchers at the Kumamoto Sanctuary in Japan conducted a study in which they observed 16 chimpanzee males and 4 females for a period of 604 hours, noting when and where they urinated.

The researchers hypothesized that recognition of other chimps urinating would encourage their own urination. Increased proximity to a urinating chimp should therefore increase this probability. By this logic, the study quantified the distance that chimps urinated to each other in three categories: within arms reach, within three meters, and over three meters. The compiled urination patterns were then compared to a randomized computer simulation of equal time, repeated in 1000 sessions.

The chimp’s observed rate of urination in close proximity was higher than in any simulated trials, confirming that chimpanzee urination patterns are synchronized and not random. The observed synchronization rate in the data was found to be significantly different compared to the average synchronization rate in the simulated sessions. This stark difference supports the hypothesis that chimpanzee urination events are temporally aligned and influenced by social factors rather than occurring randomly. This synchronization suggests a form of social contagion, where the act of urination by one individual can trigger a similar response in others, particularly when they are in close proximity.

Next, the scientists measured this data against other factors, such as dyadic (or familial) social closeness and social hierarchies. The study found no correlation with urination and social closeness, observing distinct grooming trends. This finding raises questions about the specific social dynamics that drive contagious urination, as it seems to operate independently of these traditional measures of social closeness.

But while chimps may not synchronize their urination with friends, they are certainly influenced by role models. Researchers ranked each chimp’s dominance according to David’s score: a dominance quantifying method determined by the sum of fights won and lost between individuals in a group. By identifying each individual’s ranking in the group, scientists found that higher ranked chimps had greater urinating influence over lower ones. This is likely due to meeker chimpanzees’ more impressionable nature in general, although it offers valuable markers for quantifying chimp social dynamics.

In the wild, this trend could have survival implications. While on the move, for instance, individuals urinating sporadically could leave a traceable trail for predators, posing a greater safety hazard for the group. Contagious urination could also expedite coordinated departures, as well as collectivize territorial scent-marking. More observation of wild chimpanzees is necessary to firmly draw these conclusions.

Either way, this study is only the tip of the iceberg in the largely unexplored realm of contagious behaviours. Though a simple correlation, identifying the social influence in chimps’ urination patterns is the first step in addressing societal effects on physical mechanisms in both chimps and humans — something to think about the next time a group of friends flock to the bathroom.