Afraid of Snakes? Scientists Explain Why

Research: Fear of reptiles may be universal, but it's not necessarily innate.

January 25, 2011, 4:34 PM

Jan. 26, 2011— -- Fear of snakes, spiders and other creepy crawlers is so universal that most of us probably believe we must have been born with it. It's universal, so it must be innate.

Not necessarily, according to research at several major universities.

That work suggests that we learn which things can be harmful at a very young age -- even just a few months -- because we have an evolutionary bias that predisposes us to fear things that have posed a threat throughout human history.

"What we're suggesting is that we have these biases to detect things like snakes and spiders really quickly, and to associate them with things that are yucky or bad, like a fearful voice," developmental psychologist Vanessa LoBue of Rutgers University said in releasing the research.

LoBue's co-authors of the study, published in Current Directions in Psychological Science, are David H. Rakison of Carnegie Mellon University and Judy S. DeLoache of the University of Virginia.

The research is based on experiments with infants and very young children to see if they automatically know something can be harmful, like a snake, or if they have to learn it by observing fearful faces of adults, or associating a snake with something unpleasant, like a loud shriek.

They found repeatedly that babies don't recognize something as potentially harmful until they are conditioned to do so by something in their environment, and even then they may not show actual fear for a while.

"We propose that humans have a perceptual bias for the rapid detection of evolutionarily relevant threats and a bias for rapid association of these threats with fear," the researchers conclude in their paper.

But we weren't born with it, and in some cases female babies reacted differently from male babies, possibly explaining why some little boys seem fearless of snakes and spiders and things that go bump in the night, but most little girls scream at the mere sight of a snake.

In his part of the research, Carnegie Mellon's Rakison studied 11-month-old infants to see if an image of a snake, for example, alongside a human face showing either happiness or fear, would cause them to recognize that a snake is either harmless or dangerous.

Why Do Boys and Girls Respond Differently to Snakes?

It worked for the girls, but not the boys.

He found that "11-month old girls -- but not boys of the same age -- associated recurrent threats with fearful faces," according to the study. Interestingly, when the babies were shown flowers or other non-threatening images along with faces showing either fear or happiness, it made no difference.

That suggests the presence of a bias to recognize that snakes may be threatening, but not flowers.

DeLoache and LoBue tested infants (8 to 14 months old) and 3-year-old children and adults to see if they found images of snakes more quickly in a matrix of several images than they found harmless objects, like flowers. In all three cases the participants found snakes faster than flowers.

But apparently that instant recognition wasn't necessarily driven by fear. All participants were tested to see if they were really afraid of harmful items, like snakes, or just recognized that they were not supposed to include snakes as close friends.

The kids, and the adults, who showed signs of actual fear were no faster than participants who were unafraid of snakes at zeroing in on the snakes. That suggests it was a bias to learn fear, not fear itself, that governed the performance.

Similarly, infants who were shown a fearful face along with a picture of a snake recognized that the snake was probably not a good thing, but showed no sign of actual fear (no crying, for example.)

That compelled the researchers to conclude that "to develop an actual fear of snakes or of spiders, learning is required." That fear didn't come automatically, or with the body.

The work builds on previous research by other scientists, involving both humans and monkeys.

Susan Mineka of Northwestern University in Chicago showed that monkeys raised in the lab showed no fear of snakes, but they -- like humans -- visually detected snakes more quickly than harmless images, suggesting they somehow knew snakes could be dangerous, even though they had no direct experience with reptiles.

Humans Not Born With Fear of Snakes but Conditioned to Fear Potential Threats

Mineka and her colleagues suggested that part of the brain automatically invokes a fear response based on threats to survival throughout the history of primates, so it is evolutionarily based. That may explain why persons who live in industrialized countries who have never seen a snake still fear them.

Theoretically, at least, we all have a bias to avoid things that posed problems even in ancient human history.

We aren't born with a fear of snakes. But we have been conditioned by evolution to fear things that pose a threat, so we learn soon after birth that it's not a good idea to pick up a snake.

But of course, that doesn't explain the boy in the back of the class who is about to slip a garden snake over the shoulder of the girl in the next row. How come he's not afraid of the snake?

Maybe -- and this is just a layman's opinion -- proving to the girl that he's tough overrides his evolutionary bias to offer her a piece of candy instead of the snake. After all, me Tarzan, you Jane, still stands.