The Science of Why We Sleep

Scientists know that sleep obeys our complex internal clocks, affects our every waking moment, and even tames our negative emotions. But what happens while we sleep and why have we evolved to sleep in the first place? In this fascinating short video, PBS's Joe Hanson explores the mysteries of sleep...

http://www.dailygood.org/story/1144/the-science-of-why-we-sleep-maria-popova/