Three-year-olds show a bias for spotting snakes in a striking posture

Have we evolved to detect this threat?

We humans seem to have an innate predisposition to fear dangerous animals and other hazards that would have imperilled our ancestors - a phenomenon called 'prepared learning'. For example, when researchers in the 1980s used loud noises to condition people to fear the sight of snakes and guns, they found that people acquired a fear of the snakes much more easily, even though the noises matched the sound made by guns. A new study has built on that classic work by showing that children as young as three seem to be particularly adept at spotting snakes in a 'striking pose'.

Nobuo Masataka and his colleagues presented their participants with three-by-three arrays of pictures of snakes and flowers on a touch-screen. On each trial, eight of the pictures were of flowers with one snake picture, or vice versa, and the task was to touch the odd-one-out picture as quickly as possible. Twenty three-year-olds, 34 four-year-olds and 20 adults took part.

Participants of all ages were significantly quicker at the task when spotting a snake among flowers than when spotting a flower among snakes. For example, the three-year-olds took an average of 2735ms when a snake photo was the target compared with an average reaction time of 3283ms when the target was a flower. This was the case even though the children's parents said their offspring hadn't previously been exposed to real or toy snakes.

What's more, all the participants were extra quick at the task when the target picture was a snake in a striking pose: with the body coiled, the neck held in an s-curve and the head poised to strike. The three-year-olds' average reaction time for snakes in a strike pose was 2452ms compared with 2519ms for snakes in a resting position.

The new finding builds on the classic research into prepared learning by suggesting that there is a prototypical snake posture that humans are innately sensitive to. 'When a striking posture is taken by snakes,' the researchers explained, 'they display their specific morphological characteristics as signals towards the presumptive signal receivers so that the receivers will categorise them as snakes as efficiently as possible, be threatened and withdraw.'

An interesting question for future research is whether this is an evolutionary adaptation in snakes or in humans. In other words, did snake appearance and behaviour evolve in a way that exploited existing perceptual biases in humans and other animals, or did the human perceptual and attentional system evolve in such a way to become particularly attuned to snakes and snake behaviour?
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Masataka, N., Hayakawa, S., and Kawai, N. (2010). Human Young Children as well as Adults Demonstrate ‘Superior’ Rapid Snake Detection When Typical Striking Posture Is Displayed by the Snake. PLoS ONE, 5 (11) DOI: 10.1371/journal.pone.0015122