Fears

I watched a show talking about people fears and where they came from the shocking thing for me is they were normal things people are scared of.Drowning,ghost being burned alive all normal fears but i would be surprised if they would bring up fears like people who are scared of pickels mustard,and red lights.I am very scared of Aliens they horrify.But what makes us scared of these things what in our brain tells us to fear ?Those are questions i would have liked those questions answered.