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Fear of spiders, snakes innate in us
June 19, 2018, 1:07 pm

Previous studies have shown that one to five percent of the population in developed countries is affected by a real fear of spiders and snakes, even though in most of those countries there are nearly no spiders or snakes that pose a threat to humans.

However, the drawback of most previous studies on this topic was that they were conducted with adults or older children, making it hard to distinguish which behavior was learnt and which was inborn.

Now, scientists at the Max Planck Institute for Human Cognitive and Brain Sciences (MPI CBS) in Leipzig and the Uppsala University, Sweden, have made a crucial observation: Even infants at the age of six months, when they are still very immobile and have no knowledge of whether these animals are dangerous, produce a stress reaction when they see a spider or snake.

The researchers found that when shown pictures of a snake or a spider, instead of a flower or a fish, the babies reacted with significantly bigger pupils. Under constant light conditions, this change in the 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, said the researchers.

"We conclude that the fear of snakes and spiders is of an evolutionary origin. 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 other factors, it can develop into a real fear or even phobias. "A strong panicky aversion exhibited by the parents or a genetic predisposition for a hyperactive amygdala, which is important for estimating hazards, can mean that increased attention towards these creatures becomes an anxiety disorder."

Interestingly, it is known from other studies that babies do not associate pictures of rhinos, bears or other theoretically dangerous animals with fear. "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.

For modern risks such as knives, syringes or sockets, presumably the same is true. From an evolutionary perspective they have only existed for a short time, and there has been no time to establish reaction mechanisms in the brain from birth. "Ask any parent and they will tell how difficult it is to teach their children about poking their fingers into an electric socket.

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