Contagious urination has been documented among chimpanzees in Kumamoto, Japan. Researchers suggest it may help strengthen social bonds within a group. (Image credit: Kumamoto Nature Reserve)
Chimpanzees tend to urinate at the same time as other members of their group, a phenomenon scientists have described as “contagious urination.”
Experts note that since humans often go to the toilet together, and chimpanzees are our closest living relatives, this social behavior may date back to our common ancestor.
“We recognize that in humans, the decision to urinate may be influenced by social circumstances that prompt us to urinate at the same time as others, and that such simultaneous urination may further strengthen social bonds,” study co-author Shinya Yamamoto, a wildlife researcher at Kyoto University, told Live Science in an email. “Our study with chimpanzees clearly demonstrates that they have some analogies in this phenomenon, indicating that contagious urination has deep evolutionary roots.”
The team decided to investigate this behaviour after noticing that a group of chimpanzees at a zoo had a habit of urinating at around the same time, and wondered whether this might be similar to the contagious yawning seen in other primates and wolves.
In a study published Monday (January 20) in the journal Current Biology, scientists monitored 20 captive chimpanzees in Japan's Kumamoto Nature Reserve for more than 600 hours.
They found that when one chimp in a group urinated, others tended to follow suit. The researchers recorded the number of urinations that occurred over 60 consecutive seconds and then matched the data with randomized computer models. The results showed that this contagious urination behavior was enhanced by close physical contact, so that chimps observing another chimp urinating nearby were more likely to follow suit.
Scientists have found that social status influences the contagiousness of urination: individuals with lower social status are more likely to urinate when others do so.
Social rank also influenced this behavior: chimpanzees with lower dominance status were more likely to urinate when others urinated. Social closeness, as measured by time spent in the presence and grooming of another chimpanzee, had no effect on this urination phenomenon—unlike social yawning, which increases in close social pairs.
Researchers say contagious urination may have significant implications for social group cohesion, coordination, or strengthening social bonds.
This behavior may exist to promote “state matching” when the chimpanzee
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