Image: JJ Harrison, Wikimedia Commons

Many people cringe at the idea of a spider walking up their arm or a snake slithering across their foot — and a fascinating new study shows we may actually be born with this fear.

Scientists at the Max Planck Institute for Human Cognitive and Brain Sciences studied the body’s response to these creatures in an age group least influenced by environmental factors — infants. The goal of this new study was to determine whether or not humans are born with an inherent fear of snakes and spiders or whether it develops as we age.

Researchers tested forty-eight six-month old infants. The infants were held in their parents’ lap and the parents given glasses so that their physiological responses did not influence their children’s. The infants were shown a picture of a snake, spider, or a benign object such as a fish or a flower.

Image: Max Planck Institute for Human Cognitive and Brain Sciences

The babies displayed a stress response when shown pictures of snakes or spiders: enlarged pupils, as opposed to when shown pictures of fish or flowers. Dilated pupils indicate activity in the brain within the noradrenergic system, which is correlated with stress.

Spiders and snakes have coexisted with humans for upwards of 40-60 million years, attributing to the possibility that an evolutionary fear has become imbedded in the brain.

“We conclude that fear of snakes and spiders is of 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,” states Stefanie Hoehl, lead investigator of the study.

But what about spider enthusiasts? One theory that might explain the discrepancy between avid pet keepers and those with intense arachnophobia is that their attitudes are learned as they grow older.

The complete study is published in Frontiers in Psychology.