Despite the fact that in industrialised locales, most people may not encounter snakes or spiders, the fear of such a creature crawling up your hand can cause shudders in some. Researchers working on this find that even babies are not exempt from this fear. Even infants who were too young to have seen a spider or snake showed signs of stress when shown a picture of a spider or snake as evidenced by dilation of pupils.
Interestingly, other studies have shown that infants do not show fear when shown pictures of rhinos, bears or other dangerous animals.
They deduce that since spiders and snakes have coexisted with humans for about 60 million years, the fear could have become embedded in the brain during evolution.