Chimpanzees tend to pee when other members of their group do, a phenomenon that scientists have dubbed “contagious urination.”
Since groups of people often go to the bathroom together and chimpanzees are our closest living relatives, this social behavior could trace back to our common ancestor, the researchers said.
“In humans, we know that our decision to urinate is influenced by social contexts that lead us to urinate simultaneously with others, and that this simultaneous urination could also promote more social bonds,” co-author of the study. Shinya Yamamotowildlife researcher at Kyoto University, told Live Science in an email. “Our study with chimpanzees clearly shows that they share some similarities in this phenomenon, suggesting the deep evolutionary origin of contagious urination.”
The team decided to study this behavior after noticing that a group of chimpanzees at a zoo tended to urinate around the same time and wondered if it might be similar to contagious yawning, seen in other primates And wolves.
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For the study, published Monday January 20 in the journal Current biologyResearchers observed 20 chimpanzees in captivity at the Kumamoto Sanctuary in Japan for more than 600 hours.
They found that when one chimpanzee in the group peed, the others were more likely to follow. The researchers recorded the number of urinations that occurred 60 seconds apart, then compared this data with randomized computer simulations. The study found that this contagious urination behavior increased with physical proximity, such that chimpanzees seeing another chimpanzee near them pee were more likely to do the same.
Social rank also influenced this behavior: chimpanzees with lower dominance rank were more likely to pee when others were peeing. Social proximity, measured by time spent in proximity and grooming with another chimpanzee, had no effect on the peeing phenomenon, unlike social yawning, which increased over time. socially closer couples.
Contagious urination could be important for the cohesion, coordination or strengthening of social bonds of social groups, the researchers said.
This behavior could exist to encourage “state matching,” in which chimpanzees improve group cohesion by all being in a similar state, study co-author Ena Onishiwildlife researcher at Kyoto University, told Live Science in an email. This behavior could also strengthen social bonds.
Another possibility is that multiple chimpanzees urinating in the same location may deter or confuse predators, reducing the risk of being tracked by scattered urine odors.
Although no similar studies have yet been conducted on chimpanzees in the wild, some researchers have noted similar behaviors in wild populations, Onishi said. Researchers are also curious if other species exhibit this contagious urination behavior.
“We are greatly influenced by the presence of others, even in mundane activities,” Onishi said. “For example, in both chimpanzees and humans, behaviors such as yawning, walking, rhythmic tapping, and even pupil size are known to be contagious.”
Studying contagious urination could help scientists understand the behavior of humans’ common ancestors with chimpanzees, as well as the origin of this social custom in humans, Onishi said.