Your Ancestors Didn't Sleep Like You

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Your grandparents probably slept like you. And your great, great-grandparents. But once you go back before the 1800s, sleep starts to look a lot different. Your ancestors slept in a way that modern sleepers would find bizarre - they slept twice.
We used to sleep in two shorter periods, over a longer range of night. This range was about 12 hours long, and began with a sleep of three to four hours, wakefulness of two to three hours, then sleep again until morning.