Fear of snakes: An evolutionary perspective on the way kids learn
© 2011 Gwen Dewar, Ph.D., all rights reserved
Know a child with a disgust or fear of snakes?
How about a fearful toddler? Or baby?
aren’t born with such responses. We know that from experiments on
infants. If you show snakes to 7-month old babies, they don’t act
frightened at all.
How—and when—do these fears first appear?
to the idea of classical conditioning, people and other animals become
frightened of a thing if they’ve experienced something nasty (like a
shock) each time they encounter it.
But this process seems inefficient. Does a monkey need to get attacked in order to learn a fear of snakes?
If so, how many monkeys would survive to adulthood?
the reality is this: Animals have ways of learning about dangerous
things that don’t depend on first-hand experience. They can learn about
predators by watching other members of their own species.
group of monkeys encounter a snake, the babies and juveniles watch how
the adults react. They learn to cry out, to alert other members of their
family, to get out of the snake’s reach. They learn to be afraid.
That’s fascinating enough.
Humans aren’t the only creatures that pass knowledge from parents to offspring.
But there’s even more going on, and it concerns the way human children learn about danger:
Our brains might come equipped with special mechanisms that help us learn more quickly about certain kinds of animals—the animals that have posed the greatest threats to our ancestors.
Forty years ago, Martin Seligman proposed the idea that animals are “prepared" to learn some lessons very fast.
example concerns potentially poisonous foods. Ever notice what happens
if you happen to feel ill (and vomit) after eating a new food? You don’t
want to try it again. For some people, it takes only one bad experience
to learn this lesson—whether or not the food really is to blame.
snakes and spiders are like that. Maybe it takes very little to
trigger our fear or disgust. We see friends or family act fearfully, and
we’re persuaded. We don’t need a lot of time for the lesson to sink in.
Our brains see a snake, receives the social input and says “Oh yes,
your friends are right--those things are BAD."
evidence? Fast forward to the 1980s, when Michael Cook and Susan Mineka
(1989) conducted classic experiments on captive rhesus monkeys.
primates had never been in the wild, and they’d never before seen a
snake. If you showed these monkeys a toy snake, they didn’t react
So the researchers tried this. They divided the monkeys into two groups, and showed each group a different “spooky" video:
• Group One watched a video of a monkey acting frightened of a plastic flower.
• Group Two watched a video of a monkey acting frightened of a plastic snake.
The videos had been carefully edited to make it appear that the protagonist was equally fearful of both objects. But the videos were not equally effective.
after watching these videos, you gave a monkey a plastic flower, he
wasn’t likely to react. But if you gave him a plastic snake, he showed
In a similar experiment, monkeys rapidly learned to fear a toy crocodile but not a toy rabbit.
results were exciting. The monkeys had developed a fear of snakes(and
crocodiles) after a few, brief experiences watching another monkey on
TV. It wasn’t a general response to social cues because the monkeys
seemed relatively resistant to “catching" a fear of flowers or rabbits.
And it made sense that primates might have evolved specialized brain mechanisms for learning to fear snakes and crocodiles.
and crocs kill primates, and have done so for millions of years. So
spotting these predators was a high-stakes game. And when the stakes are
high enough, individuals who are quick to trust social cues about
predators have a fitness advantage (Dewar 2003).
But what about
human primates? Is there any evidence that human children are “prepared"
by natural selection to learn that snakes are dangerous?
Detecting snakes in the grass
Child psychologists Judy DeLoache and Vanessa LoBue have found that American preschoolers are good “snake detectors."
you show three-year-olds a set of eight photographs—seven depicting
caterpillars and one showing a snake—they are pretty quick to find the
snake. By contrast, they take longer to find the caterpillar in a group
of snake photos. The same thing happens when you ask kids to distinguish
snakes and frogs. Picking out snakes seems to be easier (LoBue and DeLoache 2008).
and LoBue have also tested the way babies—some as young as 7 months
old--react to snakes and the sound of human fear (Deloache and LoBue
In one experiment, the researchers established that babies
don’t respond fearfully to the sight of snakes. Not if the snakes are on
video and the babies aren’t given any social hints that snakes are
Next, the researchers asked a different question: Do babies respond differently to snakes if they hear adults sounding fearful?
To find out, LoBue and DeLoache presented 48 infants with a special “snake show."
baby sat with his or her mother while two silent videos—running side by
side—played simultaneously. One video showed an undulating snake. The
other video depicted a non-snake moving at approximately the same speed.
The moms were blindfolded so they couldn’t give their babies any cues.
Babies watched videos for a total of 12
trials—each trial pairing a different snake video with a video of a
different non-snake (giraffe,rhinoceros, polar bear, hippopotamus,
elephant, and large bird).
And here’s the important part. In half
the trials, the videos were accompanied by an auditory track of an
adult speaking in frightened tones. In the remaining trials, the videos
were paired with a happy adult voice.
When given the choice, which videos did the babies watch?
It depended on the context.
When the videos were accompanied by the sound of an adult's fearful voice, the babies spent more time looking at the snake video.
When the videos were matched with the sounds of a happy voice, babies did not pay any special attention to the snake.
The mounting evidence for evolutionary biases
Have scientists demonstrated that there are specialized
“snake-detectors" in the brain? Can we conclude that humans are
“hard-wired" for speedy learning about snakes?
Not yet. We have to
consider the possibility that these children had already learned
something about snakes (or the other animals) before they participated
in the experiments.
And even if we assume that the kids were
“snake naïve," it’s not yet clear how specifically snake-like an object
must be to trigger these effects.
But DeLoache and LoBue have
narrowed the possibilities. In a follow-up to the video test, they ran a
similar experiment using still photographs. This time, babies didn’t
pay any special attention to snakes—regardless of what sorts of voices
So LoBue and Deloache suspect it’s the distinctive writhing movement of snakes that really sets people off.
Meanwhile, I think the “prepared learning" hypothesis deserves our serious attention.
a related line of research, anthropologist Lynn Isbell has argued that
snakes have driven the evolution of primate 3-D, color vision—the better
to detect serpentine predators (Isbell 2006).
And I’m intrigued
by the results of another “snake detection" experiment—one like the
“find the snake among the caterpillars" study, but with an interesting
In this experiment, Nobuo Masataka and colleagues (2010) asked people to
pick out a snake image from an array of flower images. And the twist?
In some trials, the snake was at rest. In others, the snake was in
“attack posture," coiled and prepared to strike.
What Masataka’s team found was that people were a bit faster identifying snakes when the snakes had adopted an attack posture.
And the results seem especially compelling for two reasons:
(1) The visual difference between the “resting" and “attack posture"
images was actually quite subtle (see the illustration for examples).
(2) The effect was found in both adults AND young children (aged 3-4).
to their parents, these young children had never been exposed to snakes
before. Not only had they never seen a real snake, they’d never seen
any images of snakes. Or toy snakes.
If results like that can be
replicated elsewhere, that’s a pretty impressive finding. Naïve kids
spot snakes faster when the snakes are ready to strike? That’s just the
sort of thing we’d like a predator-detection system to do for us.
And, in case you are wondering , there is evidence that a distinctively fearful
reaction might help people detect snakes. In studies that compared
snake-phobic adults with their non-phobic counterparts, the
snake-fearing people were quicker at detection (Peira et al 2010; Ohman
et al 2001).
That wasn’t true for the preschoolers. Kids with
snake-fear were not any faster at detection. So perhaps the detection
advantage develops over time.
Want to read more about predator detection and the fear of snakes?
An overview of the field
Authors Vanessa LoBue, David H.
Rakison and Judy S. DeLoache have written a concise and up-to-date
review of the research on biases for detecting creepy crawlies in
children and infants:
(2010) Threat Perception Across the
Life Span : Evidence for Multiple Converging Pathways. Current
Directions in Psychological Science 19(6) 375-379.
You can also visit this page featuring many publications from
DeLoache's lab, including downloadable papers about the evolutionary basis for a fear of snakes.
Thoughts about the evolution of sex differences
snakes and spiders is more common among women. For example, in a Swedish
survey, snake or spider phobias were reported by about 12% of women but
only 3% of men (Frederickson et al 1996).
Why the difference?
Some researchers speculate that ancestral females were under greater
selective pressure to avoid snakes and spiders--either because they
encountered them more often (during foraging) or because they had to be
extra-vigilant in order to protect the young children in their care.
there support for the idea that females have a stronger evolutionary
bias for responding to snakes? DeLoache and LoBue haven’t found any sex
differences in snake-detection abilities of young children.
other research suggests that baby girls might be faster at learning to
associate snakes and spiders with fearful faces (Rackison 2009).
I discuss this research--and question the reliability of surveys about the fear of snakes--in this article "Is snake fear a girly thing?"
You can also read
David Rackison’s scientific paper, "Does women's greater fear of snakes and spiders originate in infancy?"
References: Fear of snakes
Cook M and Mineka S. 1989. Observational condition of fear to
fear-relevant versus fear-irrelevant stimuli in rhesus monkeys. Journal
of Abnormal Psychology 98 (4): 448-459.
DeLoache J and LoBue V.
2009. The narrow fellow in the grass: Human infants associate snakes and
fear. Developmental Science 12: 201–207.
Dewar G. 2002. The cue
reliability approach to social transmission: designing tests for
adaptive traditions. In: DM Fragaszy and S. Perry (eds), The biology of
traditions: Models and Evidence. Cambridge University Press.
M, Annas P, Fischer H, and Wik G. 2001. Gender and age differences in
the prevalence of specific fears and phobias. Behav Res Ther.
Isbell, L.A. 2006. Snakes as agents of evolutionary change in primate brains. Journal of Human Evolution 51:1-35
V and DeLoache JS. 2008. Detecting the snake in the grass: Attention to
fear-relevant stimuli by adults and young children.Psychological
Science, 19, 284–289.
Masataka N, Hayakawa S, and Kawai N. 2010.
Human young children as well as adults demonstrate 'superior' rapid
snake detection when typical striking posture is displayed by the snake.
PLoS One. 5(11):e15122.
Peira N, Golkar A, Larsson M,
Wiens S. 2010. What you fear will appear: detection of schematic spiders
in spider fear. Exp Psychol. 57(6):470-5.
Rackison D. 2009. Does women's greater fear of snakes and spiders originate in infancy? Evolution and Behavior. 30(6): 439–444.
Seligman MEP. 1970. On the generality of the laws of learning. Psychological Review 77(5): 406-418.
Content of "Fear of snakes" last modified 1/11
image of woman and snake ©iStockphoto.com/John Evans;
image of boa constrictor by Belizian/wikimedia commons