Why Do We Sleep?

Sleep consumes time we could spend foraging and it exposes us to predators.  It’s a waste and a risk.  So why do humans sleep?  Why didn’t nature design us for continual activity and vigilance?

In the October 18, 2013 Science, researchers offer an answer:  sleep enables house cleaning.  Studies of mice show that sleep sweeps the brain of toxic metabolic waste products.

Ergo, at the day’s end we can say to our loved ones:  Good night.  Sleep tidy.