(NEW YORK) -- 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.
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.
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