What does fear COME from?

A couple questions...

1) Where did the factor of fear origonally come from?

2) How does the human mind react to fear? I mean how do we react when we feel scared?

3) Why do we feel scared while watching Scary Movies?

These questions came up to me
Update: OMG! I cant pick the best answer because they are all so good I understand now about how its a defence mechanism and if we didnt have that then we would kill ourselvs. Its what prevents us from doing stupid things. I get it know THANK YOU SO MUCH! It was just a question that came up so I might ask more lol show more OMG! I cant pick the best answer because they are all so good

I understand now about how its a defence mechanism and if we didnt have that then we would kill ourselvs. Its what prevents us from doing stupid things.

I get it know

THANK YOU SO MUCH!

It was just a question that came up so I might ask more lol
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