Scientists at Kyoto University have discovered that chimpanzees, like humans experiencing contagious yawning, tend to urinate when they observe their peers doing the same. The research, published in Current Biology, reveals new insights into primate social behavior and its evolutionary significance.
The study originated from observations at Kumamoto Sanctuary in Japan, where researchers noticed that captive chimpanzees appeared to urinate simultaneously. Ena Onishi from Kyoto University's Wildlife Research Centre led the investigation, noting in Cosmos magazine, "Since there were no prior studies on contagious urination in any species, we drew parallels to contagious yawning, another semi-voluntary physiological behavior."
The research team analyzed 600 hours of video footage documenting 1,328 urination events among 20 chimpanzees. They compared the timing of urination incidents occurring within one minute of each other against randomized computer simulations to establish whether the behavior was truly synchronized rather than coincidental.
The findings confirmed that the chimpanzees did coordinate their urination timing, with physical proximity emerging as a crucial factor. Unlike contagious yawning, which occurs more frequently among socially bonded individuals, the synchronized urination appeared independent of social relationships.
Social hierarchy played a notable role in the behavior pattern. "We observed a clear influence of social rank, with lower-ranking individuals being more likely to follow the urination of others," Onishi explained. This observation suggests the behavior might serve as a mechanism for maintaining social cohesion within the group.
Study co-author Shinya Yamamoto of Kyoto University drew parallels to human behavior, telling Live Science, "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 further social bonding. Our study with chimpanzees clearly shows that they share some similarities in this phenomenon, suggesting the deep evolutionary origin of contagious urination."
The researchers proposed that synchronized urination might serve additional evolutionary purposes, such as confusing predators by dispersing scent markers across multiple locations rather than creating a single traceable trail. However, they emphasize that further research is needed to fully understand the mechanisms driving this behavior in chimpanzees.
The research team noted in their publication that "socially contagious urination may be an overlooked, and potentially widespread, facet of social behavior."