Children and Monsters

Part of the reason that children are afraid of the dark may be that, in our entire evolutionary history up until just a moment ago, they never slept alone.  Instead, they nestled safely, protected by an adult - usually Mom.  In the enlightened West we stick them alone in a dark room, say goodnight, and have difficulty understanding why they’re sometimes upset.  It makes good evolutionary sense for children to have fantasies of scary monsters.  In a world stalked by lions and hyenas, such fantasies help prevent defenseless toddlers from wandering too far from their guardians.  How can this safety machinery be effective for a vigorous, curious young animal unless it delivers industrial-strength terror?  Those who are not afraid of monsters tend not to leave descendants.

 - Carl Sagan, The Demon-Haunted World (1997)