How modern life fundamentally changed the way we sleep

CContinuous Sleep is a modern HabitThere are no evolutionary constants, which helps explain why many of us still wake up at 3 a.m. wondering if something is wrong. It may help to know that this is a deeply human experience.

For most of human history, eight consecutive hours of napping was not the norm. Instead, people typically slept in two shifts each night, often referred to as “first sleep” and “second sleep”.

Each of these sleeps lasted several hours, separated by intervals of wakefulness of an hour or more in the middle of the night. Historical records from Europe, Africa, Asia, and beyond describe how, after nightfall, Family He used to go to sleep early, then wake up for a while around midnight and sleep till morning.

Dividing the night into two parts probably changed the nature of time. The quieter intervals gave the nights a clearer middle, which could make long winter evenings feel less continuous and easier to manage.

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The midnight interval was not dead time; This time is observed, which shapes how long the nights are. Some people would get up to do things like lighting a fire or checking on animals. Others stayed in bed to pray or contemplate the dreams they had just had. Letters and diaries from the pre-industrial period mention people using quiet time to read, write, or even socialize quietly with family or neighbors. Many couples take advantage of this midnight vigil for intimacy.

There are references to “an hour that ends the first sleep” in the literature of the ancient Greek poet Homer and the Roman poet Virgil, indicating how common the two-night night was.

How we lost the ‘second sleep’

The extinction of second sleep was caused by profound social changes over the past two centuries. artificial Light Is one of them. In the 1700s and 1800s, first oil lamps, then gas lighting, and eventually electric lighting began to turn nighttime into a more useful time of wakefulness. Instead of going to bed soon after sunset, people started staying awake by the light of lamps until late in the evening.

Biologically, bright light at night also alters our internal clocks (our circadian rhythm) and our bodies have a reduced tendency to wake up after a few hours of sleep. Light timing matters. Normal “room” light before bed suppresses and delays melatonin, which subsequently prolongs sleep onset.

The Industrial Revolution changed not only the way people worked but also the way they slept. The factory schedule encouraged a block of rest. By the beginning of the 20th century, the idea of ​​eight uninterrupted hours had replaced the age-old rhythm of two sleeps.

In multi-week sleep studies that simulate long winter nights in darkness and remove clocks or evening lights, people in laboratory studies often adopt two sleep cycles with intervals of calm wakefulness. A 2017 study of a Madagascan farming community without electricity found that people still mostly slept in splits, waking up around midnight.

long, dark winters

Light determines our internal clock and affects how fast we perceive time passing. When those signals fade, such as in winter or artificial light, we drift off.

In winter, late and weak morning light makes circadian alignment difficult. Morning light is especially important for regulating circadian rhythms because it contains high amounts of blue light, which is the most effective wavelength for stimulating cortisol production in the body and suppressing melatonin.

In time-isolated laboratories and cave studies, people have lived for weeks without natural light or clocks, or even in continuous darkness. Many people in these studies miscalculated the number of days passing, which showed how easily time passes without any light signal.

Similar distortions occur in polar winter, where time can feel frozen due to the absence of sunrise and sunset. Natives of high latitudes and long-term residents with stable routines often cope better with polar light cycles than short-term visitors, but this varies by population and context. For example, residents adapt better when their community shares regular daily schedules. And a 1993 study of the Icelandic population and their descendants who immigrated to Canada found that these people had unusually low winter seasonal affective disorder (SAD) rates. The study suggests that genetics may help this population cope with the long Arctic winter.

Research from the Environmental Temporal Cognition Lab at Kiel University, where I am director, shows how strong this connection is between light, mood and time perception. In 360-degree virtual reality, we matched scenes from the UK and Sweden for setting, light level cues and time of day. Participants watched six clips of approximately two minutes each. They found the two-minute interval to last longer in evening or dimly lit scenes than in daytime or brightly lit scenes. Its effect was greatest among participants who reported low mood.

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A new perspective on insomnia

Sleep physicians say brief awakenings are normal, often appearing during phase changes, including near REM sleep, which is associated with vivid dreaming. What matters is how we respond.

The brain’s sense of duration is elastic: anxiety, boredom, or low light stretch time, while busyness and peace can compress it. Without that interval where you used to get up and do something or interact with your partner, waking up at 3 a.m. often makes time seem slower. In this context, attention is focused on time and the minutes that pass may seem longer.

Cognitive behavioral therapy for insomnia (CBT-I) recommends people leave the bed after waking up for about 20 minutes, do a quiet activity like reading in dim light, then return when they feel sleepy.

Sleep experts also suggest covering the clock and quitting measuring time when you’re struggling to sleep. A calm acceptance of awareness, coupled with an understanding of how our brains perceive time, may be the safest way to relax again.