Girls have head start on snake and spider fears

Gut-wrenching fears of snakes and spiders may start early for many women. Before their first birthdays, girls but not boys adeptly learn to link the sight of these creatures to the frightened reactions of others, a new study suggests.

Neither infant girls nor boys link happy faces with snakes and spiders, reports study author David Rakison of Carnegie Mellon University in Pittsburgh in an upcoming Evolution & Human Behavior. Youngsters of both sexes also don’t tend to associate images of flowers and mushrooms with either fearful or happy faces, he finds.

In Rakison’s tests, 11-month-old babies first looked at pairs of images—a happy or fearful cartoon face was paired with a snake, spider, flower or mushroom. After the first brief display, Rakison timed how long each child gazed at new pairs of images. A youngster who learned to associate two images, say a fearful face with a snake, would gaze longer at a violation of what he or she expected to see, such as a happy face with a snake, the researcher reasoned.

Only girls associated the snake or spider that they originally saw with a fearful reaction and then acted on that knowledge, looking longer at the unexpected appearance of a happy face with a new snake or spider, Rakison proposes. No other pair of images elicited longer gazes from girls or boys.

If confirmed in further studies, these findings support the idea that people have evolved a brain mechanism that primes them for learning to pair fear expressions with threats that would have repeatedly confronted prehistoric populations, Rakison proposes. In his view, bites from poisonous snakes and spiders presented a special danger to prehistoric women, whose children would have died or incurred great hardship without their mothers.

Surveys of adults and children find that 5.5 percent report snake phobias and 3.5 percent report spider phobias. These particular phobias affect roughly four times more women than men.

“The basis for women’s greater incidence of fear and phobias for snakes and spiders may be an evolved fear mechanism that operates during infancy and is especially sensitive in females,” Rakison says.

It’s not known whether 11-month-old girls’ tendency to pair fearful expressions with snakes and spiders continues to operate during childhood and contributes to the emergence of phobias, Rakison notes.

Males also develop fears and phobias about snakes and spiders, Rakison adds. But he theorizes that risk-taking personalities offered greater survival value for men in prehistoric times, when they had to hunt, defend their families and occasionally fight other groups.

A simpler form of learning may explain the new findings, comments psychologist Vanessa LoBue of the University of Virginia in Charlottesville. Infants of both sexes may be equally primed to acquire a fear of snakes and spiders. But if 11- month-old girls generally recognize facial expressions better than their male peers, that would give infant girls an advantage at pairing fearful faces with snake and spider images.

In an unpublished review of her earlier studies, LoBue concludes that 5-year-old girls recognize both threatening and non-threatening facial expressions more quickly than boys. But it’s not yet known if 11-month-olds display the same sex difference.

She suspects that infants of both sexes are predisposed to fear snakes’ slithering motion. In the January Developmental Science, LoBue and University of Virginia psychologist Judy DeLoache reported that 7- to 18-month-olds of both sexes look longer at movies of snakes while listening to frightened, versus happy, voices. But the same infants did not look longer at still images of snakes paired with a frightened voice, compared with snake images accompanied by a happy voice.

Further research needs to establish whether the sex difference reported by Rakison vanishes as boys become more experienced at decoding faces, in LoBue’s opinion.

“From an evolutionary perspective, it makes the most sense for both boys and girls to learn quickly to fear threatening stimuli such as snakes and spiders, but gender differences in fear learning warrant further investigation,” LoBue says.

Rakison’s new study included two experiments, each with 10 infant boys and 10 infant girls. Before testing, Rakison confirmed that neither boys nor girls had an initial tendency to look longer at any one type of image. In the first experiment, he found that girls, but not boys, quickly learned to connect pictures of snakes and spiders with a scared-looking face. In the second experiment, girls and boys alike did not learn to pair either a happy or fearful face with mushrooms or flowers.

Rakison is now repeating these experiments with larger groups of 11-month-olds. He also plans to examine infants’ ability to associate snakes and spiders with the scared and happy faces of adults, rather than cartoons.