I have a friend who says three in the morning is the time we all spend laying awake, staring at darkness, and thinking about all the mistakes we’ve made in our lives. Everyone reading this knows that she’s right. But it doesn’t need to be this way. We could use this time productively, the way our ancestors did.

Exactly how long we're supposed to sleep each night can vary depending on who you talk to, but we all seem to agree on one thing: you want to get one long, uninterrupted sleep. But it wasn't always that way.