Why we stopped sleeping twice a night

For much of history, people didn’t sleep in a single eight-hour block. In diaries, medical texts and court records from pre-industrial Europe and beyond, nights were often split into a “first sleep,” a quiet waking hour or two, then a “second sleep.” That middle spell, sometimes called the “watch”, was used for prayer, conversation, reading, sex, or simple reflection in the dark. Historian Roger Ekirch’s archival work, and a small NIMH experiment where volunteers lived without artificial light and naturally drifted into two sleep bouts, helped revive awareness of this older pattern.

How light and schedules squeezed the night

So why did segmented sleep fade? In a word: light, followed by schedules. Gaslight and then electric bulbs stretched evenings, delaying melatonin release and nudging bedtimes later. Once mornings stayed the same because factory whistles, rail timetables and office hours didn’t budge, the long winter night that once accommodated two sleeps got squeezed into a single block. Over the 19th and 20th centuries, the cultural ideal of “a solid night’s sleep” took root, reinforced by schooling, commuting and mass media.

Is biphasic sleep “more natural”?