Ever wondered why you fear spiders, even though you live in a place where there are no poisonous arachnids lurking around?
New research suggests our fear of spiders and snakes might have an evolutionary origin.
Scientists from the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) in Leipzig and Uppsala University, Sweden, say 1-5% of the population in developed countries are affected by a phobia of these creatures.
This made them want to investigate whether the fear is inborn or something that is learnt from the surroundings as a child.
The researchers conducted two experiments with six-month-old infants. In the first one, the babies were shown pictures of spiders and flowers as well as snakes and fish.
They used a Tobii T120 near infrared eye tracker to measure pupillary dilation in the infants as a way to gauge their stress response.
In the second experiment, the infants viewed photos of only fish or only snakes and their pupillometric data was compared.
Lead researcher Stefanie Hoehl, a neuroscientist at MPI CBS and the University of Vienna, said: “When we showed pictures of a snake or a spider to the babies instead of a flower or a fish of the same size and colour, they reacted with significantly bigger pupils.
“In constant light conditions this change in size of the pupils is an important signal for the activation of the noradrenergic system in the brain, which is responsible for stress reactions.
“Accordingly, even the youngest babies seem to be stressed by these groups of animals.”
Hoehl says this suggests fear of snakes and spiders is an evolutionary trait.
She continued: “Similar to primates, mechanisms in our brains enable us to identify objects as ‘spider’ or ‘snake’ and to react to them very fast.
“This obviously inherited stress reaction in turn predisposes us to learn these animals as dangerous or disgusting.
“When this accompanies further factors it can develop into a real fear or even phobia.”
Hoehl points out that previous studies have shown babies do not associate pictures of rhinos, bears or other dangerous animals with fear.
She said: “We assume that the reason for this particular reaction upon seeing spiders and snakes is due to the coexistence of these potentially dangerous animals with humans and their ancestors for more than 40 to 60 million years – and therefore much longer than with today’s dangerous mammals.
“The reaction which is induced by animal groups feared from birth could have been embedded in the brain for an evolutionarily long time.”
The research is published in the open access journal Frontiers in Psychology.
