Dr. Nobuyuki Kawai from Nagoya University in Japan has discovered that monkeys are able to rapidly detect snakes due to the distinctive visual cue of snake scales. His research reveals an evolutionary adaptation in primates that enables them to identify snakes by specific visual traits, providing valuable insight into how threat detection may have shaped the development of visual processing in primates. These findings were published in Scientific Reports.
The ability to quickly recognize and respond to potential dangers is vital for survival. Snakes, throughout evolutionary history, have posed a significant threat to primates, including humans. This instinctive fear is evident even in monkeys and human infants who have never encountered a snake—both groups exhibit a strong reaction to pictures of snakes, underscoring our innate response to these creatures.
In his first experiment, Kawai found that monkeys immediately responded to images of snakes, but not to images of salamanders, indicating a specific fear of snakes. Based on this observation, he hypothesized that if he edited the salamander images to include snake scales, would the monkeys respond to the scales, or would they recognize the harmless salamander despite the alterations?
To test this hypothesis, Kawai showed monkeys that had never seen a real snake a set of nine images on a board and trained them to identify the image that was different in order to receive a reward. When presented with a snake among a group of salamanders, the monkeys responded more quickly to the snake than to identifying a salamander among snakes. This suggests that the monkeys had an inherent, stronger response to the potentially dangerous reptile.
However, when Kawai altered the salamander images to include snake scales, the monkeys reacted to these edited images with the same speed, or even faster, than they did to the snake images.
“Previously, we demonstrated that humans and primates can recognize snakes quickly, but the exact visual cue was unknown,” Kawai explained. “The monkeys did not respond faster to salamanders, which share a similar elongated body and tail to snakes, until the images were altered to include snake scales. This indicates that the monkeys’ reactions were triggered specifically by the scales.”
Kawai suggested that this reaction could be due to an evolutionary development in primates’ visual systems, which became attuned to recognizing snake scales as a key feature associated with danger. “These insights into primate evolution will likely enhance our understanding of visual processing and brain evolution in animals, including humans,” he concluded.