Our Brains Evolved to Recoil at the Sight of Snakes

Around 60 million years ago, our primate ancestors figured out that the sight of a snake meant trouble—a discovery that had great implications for our evolutionary trajectory. New research shows that, along with our monkey relatives, our superior vision is likely directly connected to the threat of slithering snakes, NPR reports.

In lab tests, researchers used implanted electrodes to monitor monkey brains as the primates were shown images of snakes mixed in with other images of random objects. When the monkeys saw the snakes, neurons in the brain region responsible for vision appeared especially responsive. We share this same physiology with monkeys and chimps, so presumably the findings should apply to humans as well. The sight of a snake, the researchers say, triggers an innate, evolved recoil response, even before our brains have time to consciously register “snake!” 

“We’re finding results consistent with the idea that snakes have exerted strong selective pressure on primates,” the researchers said in a release. Observations from nature seem to support this point. Monkeys and chimps that live in more snake-filled habitats have excellent vision, NPR points out, while lemurs that live on snake-free Madagascar have by far the poorest of the primate species.

More from Smithsonian.com:

Five Giant Snakes We Should Worry About 
Snakes: The Good, the Bad and the Deadly 

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Rachel Nuwer is a freelance science writer based in Brooklyn.