For a long time, researchers weren’t quite sure why we sleep. There are a number of different theories. Some are evolutionary: For instance, sleep keeps us out of trouble at night and away from animals who wake up and hunt after the sun goes down. Some are physiological: Sleep lets us conserve precious energy. And some are anecdotal: Parents joke that they’d go nuts if sleep didn’t exist, since it affords them a much-needed break from their kids. But the reality is that the brain does a lot of work while we’re sleeping—even though we’re unconscious, this doesn’t at all mean the brain is “off.” In fact, in many ways, it's incredibly "on."
by Alice G. Walton, read more in www.forbes.com/sites