There has been many studies done on this exact topic. One of the conclusions the researchers came up with was that the fear of snakes is a learned behavior. Through out our lives we are conditioned to be afraid of certain things fire, heights etc. Now all of us don't learn the same way so you have people that can be firefighters because the fear wasn't instilled the same way as to become overwhelming. The research is really interesting and I would suggest reading up on some of them.