The snake in the grass, not in the tree, made us human

In the last post I described some conditioning experiments in which researchers tested whether it was harder to extinguish peoples’ fear of snakes as opposed to fear of innocuous things or modern dangers. These experiments eventually gave way to a new paradigm in which researchers tested whether people had a perceptual bias toward detecting snakes. In other words they wanted to know whether people more easily detected a snake in the grass than say, a daffodil.

To test this they set people in front of monitors, showed them sets of pictures, and recorded the time it took to identify the odd one out. So among a set of flower pictures they included a snake picture or among snake pictures they included a single flower picture. What they found was that people more quickly spotted the snake among flowers than the flower among snakes. What’s more, it made no difference whether it was a 2 x 2 matrix of pictures or 3 x 3. The time to detect a snake was equally as fast. This suggested that yes, people do have a bias toward detecting snakes over other things.

Source: LoBue and Deloache 2008

At the same time a primatologist named Lynne Isbell theorised that this perceptual bias is a very ancient thing among us primates. Isbell’s Snake Detection Theory holds that the threat from snakes, whether as predators or things stepped upon, was a key driver in primate evolution, and by extension human evolution, fostering key attributes such as orbital convergence, trichromacy, and even declarative pointing. In other words, it was snakes moreso than brightly coloured fruits that set us on our current evolutionary pathway.

In the next installment, I’ll describe how this evolved adaptation to the danger from snakes is expressed physically in our overgrown primate brains.