At the Reptile Expo held at the SETEC in Gangnam-gu, Seoul in August, a booth staff member showcases a pet snake./Courtesy of News1

The upcoming 2025 will be the Year of the Snake in the Chinese zodiac, which already brings anxiety. Humans instinctively feel fear when it comes to snakes. The fact that even infants who have never seen a snake react strongly to snake images supports this. Japanese scientists found that the reason humans can instinctively detect snakes they have never seen lies in the same primate family as them, monkeys.

Nobuyuki Kawai, a professor of cognitive psychology at Nagoya University in Japan, noted on the 27th that monkeys use scales as clues to quickly detect snakes. The research findings were published last month in the international journal Scientific Reports.

Since primitive times, snakes have posed a deadly threat to primates, including humans. This has resulted in a defensive instinct toward snakes. According to prior research, humans and monkeys who have never seen a snake can both quickly and accurately detect snake images. Even infants aged 8 to 14 months respond faster to images of snakes than to flower images. Primates have evolved to be unconsciously afraid of snakes.

From the left, a lizard, a lizard with snake scales on its body, and a snake./Courtesy of Matsushita Reiko

Professor Kawai investigated which characteristics of snakes primates fear through experiments. When presented with images of snakes and salamanders, the monkeys immediately reacted to the snake images but did not react to the salamander images. The researchers suspected that the presence of scales, a distinguishing feature between snakes and salamanders, triggers the fear of snakes.

To confirm this, they synthesized snake scales onto salamander images and showed them to the monkeys. The experiment results showed that even monkeys who had never seen a real snake reacted to the synthesized salamander images with snake scales as quickly or even more quickly than other monkeys respond when seeing a snake. This confirmed that snake detection operates not merely on shape or size but primarily on the visual cue of scales.

Professor Kawai explained, "It was already known that humans and primates can quickly recognize snakes, but the key visual characteristics used in this process had not been clarified. This study suggests that our primate ancestors developed a defensive system capable of detecting snake scales during the evolutionary process." He added, "This research will contribute to understanding the visual and brain evolution of animals and humans."

Reference materials

Scientific Reports (2024), DOI: https://doi.org/10.1038/s41598-024-78595-w

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