Before the electric light bulb, humans across the world slept in two distinct segments separated by an hour or two of wakefulness in the middle of the night. This isn't a fringe theory — it's documented in hundreds of historical records from medieval prayer manuals to Victorian diaries. We haven't just changed when we sleep. We've changed the fundamental structure of sleep itself.
What the historical record shows
Historian Roger Ekirch spent 16 years uncovering over 500 historical references to a segmented sleep pattern in his 2005 book At Day's Close: Night in Times Past. Medieval books of hours — the prayer manuals that structured monastic daily life — scheduled prayers for the 'first sleep' and 'second sleep' explicitly, with a period of wakefulness between them called the 'watch'. Physicians in 16th-century medical texts prescribed activities for this watching period. The Tiv people of Nigeria still call their two sleep periods 'first sleep' and 'second sleep' in their native language. Court records, diaries, and literature across multiple cultures and centuries all contain the same structure. This wasn't a quirk of one culture — it was the global human norm for millennia.
What happened between the two sleeps
The period between first and second sleep — typically from around midnight to 2am — was not treated as insomnia. Historical records describe it as a quiet, reflective time when people visited neighbours, tended fires, had sex (physicians recommended this time as optimal for conception), prayed, and reflected. Robert Louis Stevenson described it. Charles Dickens referenced it. Chaucer used it in The Canterbury Tales. The brain's state during this middle waking period appears to be uniquely calm: EEG studies by Thomas Wehr at the National Institute of Mental Health found that subjects kept in natural (pre-electric-light) photoperiods spontaneously shifted to biphasic sleep, and during the waking interval showed alpha wave activity associated with deep relaxation — the same state associated with meditation.
The electric light disruption
The transition from biphasic to monophasic sleep happened rapidly after the widespread adoption of artificial light in the late 19th and early 20th centuries. Gas lighting extended social hours past darkness; electric lighting made evening productivity possible. The industrial economy imposed fixed start times that punished late rising. The result was a population that compressed two natural sleep periods into one, pushed later by artificial light. Thomas Wehr's controlled study found that subjects who spent four weeks in conditions of only 10 hours of light per day spontaneously reverted to biphasic sleep within three weeks — suggesting the pattern is still latent in human biology, suppressed rather than eliminated by modern lighting.
The modern insomnia connection
Sleep medicine researchers including Gregg Jacobs at Harvard and Till Roenneberg at Ludwig Maximilian University have suggested that a significant proportion of people who self-diagnose as insomniacs — specifically those who wake at 2–3am and cannot return to sleep — may be experiencing the latent biphasic pattern rather than a pathology. The anxiety produced by waking 'when you shouldn't' makes it harder to return to sleep, creating a self-fulfilling problem. The cultural expectation of unbroken 8-hour sleep is historically anomalous and may be producing unnecessary suffering in people whose biology is functioning exactly as evolved.
What we may have lost
Beyond the sleep architecture itself, the middle waking period appears to have served psychological functions that monophasic sleep doesn't replicate. Ekirch notes that historical accounts of this period describe a quality of thought — reflective, creative, spiritually meaningful — that differs from waking cognition. The alpha-wave state Wehr documented is associated with the kind of loose associative thinking that underlies creative insight. Carl Jung discussed what he called 'the small hours' as a uniquely productive psychological time. We cannot know whether something genuine was lost when industrial modernity eliminated this period, but the evidence suggests the question is worth asking.
“We didn't just change our sleeping habits with electric light. We erased an entire layer of human experience — the quiet, reflective middle of the night.”
Pro tip
If you wake naturally in the middle of the night and can't get back to sleep, don't panic. Try lying quietly without checking your phone for 20 minutes. The anxiety about not sleeping is often worse than the waking itself.
The invention of artificial light may have gained us productive evening hours and lost us something older and stranger — a nightly ritual of quiet wakefulness shared by every human who ever lived before us. Whether that's progress is a question worth sitting with, ideally in the dark.
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