Humans Used to Sleep Twice Every Night
Continuous sleep is a modern habit, not an evolutionary constant, which helps explain why many of us still wake at 3 am and wonder if something's wrong.
For most of human history, a continuous eight-hour snooze was not the norm. Instead, people commonly slept in two shifts each night, often called a "first sleep" and "second sleep."
- Each of these sleeps lasted several hours
- Separated by a gap of wakefulness for an hour or more in the middle of the night
Breaking the night into two parts probably changed how time felt. The quiet interval gave nights a clear middle, which can make long winter evenings feel less continuous and easier to manage.
Author's summary: Humans used to sleep twice a night.