People who are disposed to run from bees, snakes, and spiders are less likely to be harmed by them. Sometimes it is better to have a 'false positive' (to run when you don't need to) rather than a 'false negative'.

While people can have phobias of all kinds of things the main DSM subtypes (aside from 'other') may well have been the result of selection pressure. Blood/injury, insects, open spaces, heights etc.