Do humans inherit snake fear?: Primates find snakes quickly

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  • ヘビが怖いのは生まれつきか？： サルやヒトはヘビをすばやく見つける
  • ヘビ ガ コワイ ノ ワ ウマレツキ カ サル ヤ ヒト ワ ヘビ オ スバヤク ミツケル

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Abstract

Humans tend to be sensitive to threatening stimuli, such as angry faces and snakes. Humans quickly and accurately find a threatening face among a crowd of friendly faces than vice versa. A picture of snake among those of flowers is also quickly detected by humans. This quick detection has been attributed to neural circuitry that involves a direct pathway via the superior culliculs and the pulvinar nucleus of the thalamus that quickly activates the hub in the brain’s fear center, the amygdala. This starts activating defense responses via connections to the hypothalamus and the brainstem before fine information arrives from the sensory cortices. We found that even young children of three years old detected a picture of snake among flower pictures, which suggests that humans are innately sensitive to snakes. However, through learning and experiences, ontogenetic fear-relevant stimuli such as a picture of pointed gun can also trigger a quick detection. Therefore, it was not clear whether young children learned in early period of life that snakes and/or angry face are threatening via direct or vicarious learning. To elucidate whether snakes and/or angry face are phylogenetic fear-relevant stimuli, we carried out a visual search task with Japanese monkeys reared in a laboratory with no experience with snakes. The monkeys respond to pictures of snakes among those of flowers faster than vice versa irrespective of the color properties of those pictures. These results strongly suggest that primates including humans evolved to be wary of snakes. However, the results of our other study showed that monkeys showed great individual differences of fear responses in front of live snakes. These individual differences may relate to variations in the promoter region of the serotonine transporter gene（5-HTTLPR）that has been shown to influence both behavioral measures of social anxiety and the amygdala response to social threats. Our on-going analyses of length polymorphisms in the 5-HTTLPR of Japanese monkeys may shed light on variations in each individual to innately embedded threat stimuli.

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