If you’re scared of spiders and snakes, you’re not a wimp.

It could be you were born that way, according to a new study.

Researchers at the Max Plank Institute for Human Cognitive and Brain Sciences (MPI CBS) in Leipzig, Germany, found that a fear of spiders and snakes may be innate in humans, and that even babies express a stress reaction when they see a spider or snake.

That’s significant, the researchers say, because children that young are unlikely to either have encountered spiders and snakes before, or been taught that they’re supposed to be scary.

The study, published online October 18 in the journal Frontiers in Psychology, describes how scientists showed sixteen 6-month-old infants two sets of images: a card with photographs of spiders and flowers, and another card with photographs of snakes and fish. When babies saw a picture of a flower, they showed no significant reaction. But when they saw a picture of a spider the same size and color as the flower, their pupils enlarged significantly.

Lead researcher Stefanie Hoehl, a neuroscientist at MPI CBS and the University of Vienna, said that a change in pupil size is a sign that the part of the brain that controls stress reactions has been activated. Given that metric, she said, “Even the youngest babies seem to be stressed by these groups of animals."

In other words, they were scared.

And not just of spiders. The infants had the same stress reaction to photos of snakes compared to photos of fish of the same size and color.

Hoehl said this led to her team to conclude that “fear of snakes and spiders is of evolutionary origin.”

Note that Hoehl is talking about a fear, not a phobia. A phobia of spiders and snakes exists in up to 5 percent of the world’s population. And while a fear of spiders and snakes means that the sight of them might spike your heartrate, a phobia can disrupt your life. Fear means you might get the jitters if a spider crawls on your arm. A phobia means you’re physically and/or psychologically impaired by it.

Interestingly, other studies have shown that babies do not show fear when shown pictures of bears, rhinos, or other theoretically dangerous animals. Scientists theorize that’s because bears, rhinos, and our human ancestors have co-existed on this planet for thirty million years, a relatively short time, geologically speaking. Whereas spiders, snakes, and our human ancestors have co-existed for up to 60 million years, which gave humans a lot more time for our primitive brains to develop a mechanism for recognizing and responding to them as threats in our environment.

But however ancient and primitive a place that fear springs from, it hasn’t kept some babies from growing up to befriend spiders and snakes. More than 500,000 American households keep snakes as pets.

And spiders, while not as popular with pet owners, have plenty of fans as well. Tarantulas and wolf spiders are especially popular among arachnid aficionados.

So if you get the willies the next time a client comes into your practice walking a black widow, don’t worry.

It’s only natural.

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