Why does the night time/dark generate a scare factor?

Question

What makes us scared of the dark/night, biologically, and other-wise.

Answer 1

Because most people get a little nervous when they cant see whats going on around them

Answer 2

It is more instinct than anything else, fear of the unknown. being afraid of the dark developed into a basic survival tactic. You can't see a predator sneaking up on you in the dark, so if you were fearful, you were more likely to survive and carry on that fear into the next generation...

Answer 3

From a physiological stand-point, vision is the human body's primary means for determining if the current place/time/situation is a dangerous one or not.  This is why the body will make whatever efforts it can to repair an eye injury quickly (e.g., LASIK patients are back to work in 24 hours).  In the dark or in reduced visibility (same goes for extremely foggy days), there is a reduced ability to judge dangerous situations.  

Perhaps a more psychological stand-point might be the influence of folk-lore and horror movies.  The evil things come out at night!  Vampires, werewolves, ghosts, demons, Jersey Devils, chupacabras, and R.O.U.S.s are at the forefront of our imaginations when we are placed in a dark environment, and we just let the ideas run wild!  We are subconsciously drawn to think of scenes from Halloween or Final Destination or Friday the 13th as a way of keeping ourselves alert to the other senses.  People in the dark walk more slowly and try to listen for the stranger walking behind them for instance.

In short:  it's a safety mechanism to help us protect ourselves from the unknown.