Sleep is often seen as a simple, essential part of everyday life, but there are many hidden complexities behind how and why humans rest. While most people today assume that a full night’s sleep should come in one uninterrupted stretch, historical evidence suggests that sleep patterns were once very different.

Research has revealed surprising practices from the past, including segmented or biphasic sleep, where individuals slept in two shifts during the night with a period of wakefulness in between. This challenges common views about what is “normal” and raises questions about how cultural changes have influenced the way people sleep over the centuries.

Key Takeaways

Evidence shows humans once had different sleep patterns than today.
Segmented sleep was common before cultural shifts changed habits.
Understanding historical sleep can reshape perspectives on modern rest.

Paul Kern: Life Without Sleep

Kern’s Head Injury and Remarkable Recovery

Paul Kern, a Hungarian soldier serving in World War I, sustained a gunshot wound to the head in 1915 while on the Eastern Front. The bullet entered through his temple and severely damaged part of his frontal lobe. Despite this, Kern survived and made a near-complete physical recovery, which surprised those around him given the extent of his injuries.

Effects of Never Sleeping Again

After the incident, Kern completely lost the capacity to sleep. For nearly thirty-five years, he is reported to have remained awake, seemingly unaffected by his sleeplessness for most of his life. Only in his later years did he start to show signs of neurological problems, a development possibly linked to his decades without sleep.

Some experts have suggested Kern may have experienced brief episodes of unconsciousness, often called “microsleeps,” during the day. These episodes, if they occurred, were likely so brief that Kern himself did not notice them.

Notable Points:

Duration without sleep: Almost 35 years
Initial impact: No obvious health decline for decades
Later years: Neurological issues emerged

Medical Explanations for Kern’s Unique State

Medical professionals have debated how Kern managed to survive without regular sleep, which is typically viewed as critical for life. Some posit that his brain might have adapted by entering brief, involuntary periods of rest throughout the day. These micro-naps could offer a biological explanation while still highlighting the unusual nature of Kern’s circumstances.

Sleep is considered essential for all animals with a brain, making Kern’s case particularly difficult to explain using current scientific understanding. Researchers acknowledge that, despite knowing some functions of sleep—such as memory processing and toxin removal—the reason humans need extended unconsciousness and how Kern coped without it remain unresolved mysteries.

The Crucial Function of Sleep

The Necessity of Sleep for Survival

Sleep stands alongside food, water, and air as a core element needed for life. All animals with brains, including humans, require sleep to maintain basic health. Even rare cases that appear to defy this rule, such as individuals who seemingly never sleep, tend to show significant neurological issues later in life.

Key points about sleep's importance include:

Physical and mental restoration: Sleep supports essential brain processes.
Basic biological requirement: Every known animal with a brain sleeps.
Lack of sleep leads to dysfunction: Extended sleep deprivation results in various neurological problems.

Essential Needs Examples Nutrition Food and water Respiration Oxygen Restorative Sleep Multi-hour rest cycles

Questions That Remain About How Sleep Works

Despite its obvious necessity, many aspects of sleep are not fully explained by current science. Researchers know some functions of sleep, like processing memories and clearing toxins from the brain, but do not yet understand why unconsciousness is necessary for these operations.

Areas still under exploration:

Why we need to be unconscious for these processes
What mechanisms enforce the need for sleep
How sleep restores the brain and body at the cellular level

Scientific understanding acknowledges the role of sleep but lacks complete explanations for many fundamental questions.

How Sleep May Have Developed Over Time

Looking at history, it appears that humans in the past practiced segmented sleep patterns rather than sleeping in a single stretch at night. Many historical documents reference two separate periods of sleep with a window of wakefulness in between.

This pattern was observed across different cultures and eras, suggesting it could be a natural biological tendency shaped over generations. Evidence for this includes:

References in literature and court documents
Observed variations in sleep habits globally
Suggested links to pre-modern routines and environments

Segmented sleep may have been the standard for centuries, and the shift to modern single-block sleep patterns is a relatively recent change in human history.

Common Myths About How People Sleep

Belief That One Long Sleep Is Standard

Many people today believe that sleeping straight through the night in a single stretch is the universal standard. The prevalent notion is that most humans lie down at night and do not wake until morning, apart from occasional disturbances.

However, historical records suggest that for much of the past, people often divided their sleep into two segments. The typical routine involved going to bed early, then waking for a period in the night—sometimes called "the watch"—before returning to sleep. This breaks from the idea of one uninterrupted period of rest and shows that segmented sleep was once quite normal. Key activities during this wakeful interval included chores, reflection, socializing, and even prayer.

Table: Two Historical Sleep Segments

Segment Typical Time Common Activities First Sleep Early night Sleeping Wakeful Period Late night Chores, socializing, prayer Second Sleep Early morning Sleeping

Misunderstandings Surrounding Daytime Naps

A frequent comparison is made between historic segmented sleep and the modern practice of napping, especially in regions that follow an afternoon rest tradition. The siesta, often found in Mediterranean countries, usually consists of a brief nap lasting anywhere from 15 to 60 minutes in the afternoon.

Unlike the siesta, the historical pattern involved two substantial blocks of sleep at night with a wakeful period in between, rather than a primary sleep and a short daytime nap. This distinction highlights that older patterns of rest were not simply an early version of the siesta, but a completely different sleep structure altogether.

List: Key Differences Between Nighttime Segmented Sleep and Siestas

Segmented sleep features two periods of several hours at night, split by wakefulness.
Siestas are brief naps taken during daylight hours.
The nighttime pattern was widespread in various parts of the world historically, not limited to one region.

How Sleep Patterns of the Past Were Uncovered

Roger Ekirch’s Investigations into Nighttime Habits

In the early 1990s, the historian Roger Ekirch began researching the history of nighttime life. While digging through old texts and archival materials, he noticed curious phrases related to sleep. Terms such as “first sleep” appeared repeatedly, sparking his interest in how people used to sleep centuries ago.

Revealing Two-Part Nightly Rest

Ekirch started finding references indicating that people in earlier times didn’t sleep in one continuous stretch. Phrases in novels, diaries, and legal documents described a “first sleep,” followed by a period of wakefulness, then a “second sleep.” Evidence suggested that individuals would rise for a few hours in the middle of the night before returning to bed, engaging in various activities during this interval.

Typical Nighttime Routine in the Past

Time Activity ~9:00 p.m. Go to bed (“first sleep”) After a few hrs Wake up (“the watch”) 1-3 hrs Household chores, prayer, visits Late night/morning “Second sleep” Morning Awake for the day

International and Ancient Evidence

This segmented approach to sleep was not confined to medieval Europe. Findings pointed to worldwide prevalence—traces of similar descriptions appeared in ancient Greece and in various cultures across continents. From plays to legal records, thousands of historical references supported the existence of these two sleep phases.

Europe: Frequent mentions in 16th-century medical writings and English literature
Ancient Greece: Early evidence of interrupted sleep documented
Other regions: Similar customs recorded in private writings and official documents

The Forgotten Habit of Divided Sleep

The concept of spending the night in two sleeping periods, separated by substantial wakefulness, is almost unknown today. Unlike modern siestas, which are brief naps, this historical approach involved full periods of rest punctuated by hours of alertness. This way of sleeping was so widespread and natural for generations that its disappearance has become a mystery, raising questions about what led society to abandon this routine.

How Segmented Sleep Functioned

Usual Nighttime Habits

People in the past commonly started their nights by going to bed earlier than is typical today, often around 9:00 p.m. Sleep would occur in two blocks: an initial sleep phase followed by waking naturally in the early hours. The first and second sleep periods were separated by a consistent span of wakefulness.

The Middle-of-the-Night Wakeful Interval

This awake period, often called “the watch” in historical England, happened between the first and second sleep. Unlike being startled out of bed by alarms, individuals awoke naturally after several hours. The duration of this interval lasted a couple of hours before returning to sleep.

Activities Commonly Done While Awake

During this middle-of-the-night period, what people did varied. Some used the time for chores or job-related tasks, while others reflected quietly or prepared for the coming day. Socializing, paying visits to neighbors, and prayer were also widespread. There are historical mentions indicating that some viewed this time as the ideal opportunity for intimacy or personal reflection.

Examples of activities:

Household chores
Social visits
Meditation or quiet thought
Religious practices
Preparing for daytime tasks

How It Was Separate From Today’s Napping

Segmented sleep’s structure was distinct from modern napping practices like siestas. Instead of a single short nap, segmented sleep involved sleeping in two substantial blocks at night with a multi-hour awake period in between. Siestas, by contrast, are brief rests during the afternoon and do not divide nighttime sleep into two main parts. This older pattern of sleep represented a different approach to rest, spanning multiple hours of wakefulness and sleep through the night.

Early Roots and Widespread Nature of Two-Phase Sleep

Historical Clues of Broken Sleep Cycles

Mentions of first sleep and second sleep appear frequently in historical texts, especially from medieval Europe, but also in documents and literature spanning across different regions. Evidence has been uncovered in novels, plays, diaries, and even court records, which indicate that this style of sleeping in two separate periods was once widely recognized and practiced.

A notable example can be found in earlier works of Charles Dickens, where the term first sleep makes an appearance, hinting at a customary period of wakefulness between two nighttime sleep phases. Over 2,000 references like these have been identified, suggesting that split sleep was, for many centuries, a normal part of life rather than an exception.

Term Context Source Example First Sleep Literature Dickens, Medieval Books The Watch Daily Life English Tradition Second Sleep Diaries European Court Documents Wakefulness Block Social/Religious Prayers, Visits

Potential Innate Reasons for Split Nighttime Rest

The recurrence of two-phase sleep patterns around the world and throughout history has led some researchers to consider that humans may have been naturally inclined toward segmented sleep for thousands of years. This approach involves sleeping for a few hours, followed by a period of calm wakefulness, and then returning to bed until morning.

During the gap between sleep phases, people might engage in a range of quiet activities such as prayer, household tasks, personal reflection, or socializing. Researchers highlight that this early-morning activity period was not a brief nap like the siesta but rather an extended and intentional interval. The distribution and regularity of these references imply the possibility that two-phase sleep could be an inherent biological pattern for humans, rather than simply a cultural anomaly.

Notable Characteristics of Two-Phase Sleep:

Two separate multi-hour blocks of sleep at night
1–3 hours of wakefulness between sleeping phases
Varied use of wake time: chores, contemplation, visiting others, prayer
Practices similar in ancient Greece and continued for millennia

These patterns present a striking contrast to the single, uninterrupted sleep period typical in most modern societies.

Outstanding Issues and Changes in Sleep Culture

Shifts Toward a Single Sleep Period

The widespread move from split sleep to a single nightly sleep session is not fully understood. Historical texts refer to a "first sleep," hinting at an earlier pattern where people slept in two separate blocks with a period of being awake in between. This older pattern appeared across different cultures and regions, as seen in diaries, novels, and legal records.

Some possible explanations for this transition include:

Technological Advancements: The introduction of artificial lighting may have encouraged later bedtimes, making it harder to maintain segmented sleep.
Changing Work Schedules: Industrialization established structured work hours, which favored a consolidated sleep period to fit the demands of a fixed daily routine.
Urbanization: Growth of cities exposed more people to nighttime activities and distractions, reducing the appeal or possibility of waking for hours during the night.

Factor Potential Impact Artificial Lighting Shorter, delayed sleep cycles Industrial Work Schedules Single, uninterrupted sleep favored Urban Lifestyles Disruption of traditional rhythms

Unsolved Mysteries in the Study of Sleep

Despite sleep being essential for life, there are several unresolved questions about its function and evolution:

Function of Sleep: While the brain removes toxins and processes memories during sleep, the reason unconsciousness is needed for these processes is unclear.
Evolutionary Reasoning: There is debate about how sleeping for a large portion of the day or night makes sense from an evolutionary perspective.
Unique Cases: Stories such as an individual reportedly not sleeping for decades show that much remains unknown about the boundaries and requirements of human sleep.

Key Open Questions:

Why exactly did a two-phase sleep system become less common?
Was monophasic sleep truly a natural evolution, or an adaptation to changing social demands?
Are modern sleep problems connected to abandoning older patterns?
What other historical or cultural practices around sleep remain undiscovered?

Understanding these gaps may change the way society thinks about rest, work, and well-being.

The Lost Art of Biphasic Sleep: How Our Ancestors' Sleep Patterns Challenge Modern Habits