Crusaders of Light

Why are people instinctively afraid of darkness? From childhood to adulthood people still get shivers down their spine when they are in the dark. Children fear that the monster under the bed will eat them or that something will harm them, but adults grow out of that seemingly childish fear except they too fear the dark sometimes and the shiver of a presence tapping at their consciousness. Why are we all born with this fear of darkness and things that go bump in the night... it's simple it's the animal instinct warning you of the dangers. It's the survivor instinct essential to survival but what happens when you ignore the warnings of the night?