Many people have a fear of spiders, which is known by it’s name Arachnophobia. There’s even a famous horror movie about this fear. But a new study finds that we don’t learn this fear, it’s actually embedded into us at birth, and it may have been a part of our DNA for millions of years.

It’s a finding that explains why people in western, industrialized countries have this fear, despite the fact that there are almost no poisonous spiders or snakes there. The study found that babies react strongly to images of spiders and snakes compared to other creatures. It’s the first study to examine infants as opposed to adults or children.

The study tested whether the babies could spot the spiders and snakes faster, and it didn’t specifically test fear. We may have evolved this fear as long ago as 40 to 60 million years.

“When we showed pictures of a snake or a spider to the babies instead of a flower or a fish of the same size and colour, they reacted with significantly bigger pupils”, says Stefanie Hoehl, lead investigator of the underlying study and neuroscientist at MPI CBS and the University of Vienna. “In constant light conditions this change in size of the pupils is an important signal for the activation of the noradrenergic system in the brain, which is responsible for stress reactions. Accordingly, even the youngest babies seem to be stressed by these groups of animals.”

“We conclude that fear of snakes and spiders is of evolutionary origin. Similar to primates, mechanisms in our brains enable us to identify objects as ‘spider’ or ‘snake’ and to react to them very fast. This obviously inherited stress reaction in turn predisposes us to learn these animals as dangerous or disgusting. When this accompanies further factors it can develop into a real fear or even phobia. “A strong panicky aversion exhibited by the parents or a genetic predisposition for a hyperactive amygdala, which is important for estimating hazards, can mean that increased attention towards these creatures becomes an anxiety disorder.”