Monkeys detect snakes rapidly due to their scales. New experiments demonstrated that primates react strongly to snake-like scales, not just the body shape, underscoring an evolutionary adaptation in their visual systems to detect threats.
Dr. Nobuyuki Kawai of Nagoya University in Japan has discovered that monkeys’ ability to quickly detect snakes stems from their ability to recognize snake scales as a visual cue. This research underscores an evolutionary adaptation in primates, enabling them to identify snakes by specific visual characteristics. The findings, published in Scientific Reports, shed light on the evolution of visual processing mechanisms linked to threat detection.
The ability to rapidly recognize dangers is crucial for survival. Snakes have been a significant threat to primates, including humans, since the earliest stages of evolution. Remarkably, even monkeys and human infants with no prior exposure to snakes exhibit instinctive fear when shown images of these reptiles, demonstrating our innate fear of these creatures.
Experiments Unveiling the Importance of Scales
Kawai’s first experiment demonstrated that monkeys exhibited an immediate response to images of snakes but not to images of salamanders, implying a specific fear of snakes. On the basis of this observation, he wondered what would happen if he edited the images of the salamanders to have snakeskin without changing anything else. Would monkeys respond to the skin, or would they recognize the harmless salamander in snake clothing?
To answer this question, Kawai presented monkeys that had never seen a real snake with nine images on a board and trained them to find the one that was different to receive a reward. When presented with a single snake amidst a group of salamanders, monkeys exhibited a faster response time to locate the snake compared to identifying a salamander among snakes. This observation suggests that the monkeys had a strong response to the potentially dangerous reptile.
Surprising Results with Altered Images
However, when Kawai showed the edited images of salamanders with snakeskin to monkeys, they reacted to the altered images of the harmless creature equally fast, or even faster, than to the snake.
“Previously we demonstrated that humans and primates can recognize snakes quickly; however, the critical visual feature was unknown,” Kawai said. “The monkeys did not react faster to salamanders, a species that shares a similar elongated body and tail with snakes, until the images were changed to cover them with snakeskin.” This suggests that the monkeys were most threatened by the scales.
“This may be because during evolution our primate ancestors evolved a visual system to identify scales, which are characteristic of snakes,” he continued. “These insights into primate evolution will likely improve our understanding of vision and brain evolution in animals, including ourselves.”
Reference: “Japanese monkeys rapidly noticed snake-scale cladded salamanders, similar to detecting snakes” by Nobuyuki Kawai, 10 November 2024, Scientific Reports.
DOI: 10.1038/s41598-024-78595-w
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