The Full History of Human Sleep and Sleep Patterns
Dr. Nayantara Santhi, PhD
Dr. Nayantara Santhi is an associate professor of psychology at Northumbria University in Newcastle. Santhi’s body of work includes numerous articles on how circadian rhythms regulate an individual’s sleep-wake cycle. Santhi’s articles have also focused on related elements such as bright light exposure and melatonin production.
After the Industrial Revolution, many people reported sleeplessness—a condition called maintenance insomnia. A sleep historian, Roger Ekirch, states the recent invention of electricity, artificial lights, and a demand for extended workdays have caused human beings to adjust their sleep habits, causing an influx of sleep disorders, anxiety, and stress.
Between the 1600’s and 1700s, humans have switched from a biphasic sleep pattern to a monophasic sleep schedule. In other words, people stopped practicing sleeping in two periods with a 1 to 3-hour intermission and began sleeping for 8 straight hours.
In this article, we explore the history of sleep and how humans transitioned from biphasic to monophasic sleep (one sleep period). We also discuss the positive and negative sides of biphasic sleep.
The History of Sleep
Throughout time, human beings mostly slept in a segmented sleep pattern, with human physiology pushing them to sleep when its dark. Today, sleep is condensed into straight 8 hours to fit work, school, and family schedules.
Neolithic Era (10,200 BCE)
The Neolithic people stayed indoors and went to bed a couple of hours after the sunset because of the lack of light. As Dr. Santhi notes, “Human physiology is wired to be diurnal.”
Our Neolithic ancestors were accomplished builders. They made houses and villages out of mud-brick, sticks, and straw. They even constructed beds with piles of straw, down leaves, grass, and animal skins, which set them apart from the Paleolithic people.
People in the 8th millennium didn’t sleep much more comfortably than Neolithic humans, although they realized by raising their beds off the floor, bugs and pests couldn’t make nests in their beds.
Archeologists have discovered circular beds in ancient sleeping areas suggesting the fetal position was preferred during this period. Side sleeping is still prevalent in modern times as it may be a leftover instinct for self-preservation.
Physiotherapist Michael Tetley grew up among tribal people in Africa, who taught him to sleep on his side without a pillow so he could listen for danger with both ears. Tetley states, “I have organized over 14 expeditions all over the world to meet native peoples and study their sleeping and resting postures. They all adopted similar postures.”
Around this era, we have one of the earliest references to segmented sleep. It’s believed the time between the two sleep periods lasted about 1 to 3 hours and was often treated as alone time, a social period, or simply a time to get work done.
Around 500 to 450 BCE, Alcmaeon of Croton, a physician and philosopher, thought sleep was the result of blood withdrawing from the skin’s surface—this was one of the first scientific theories about sleep.
One hundred years later, Aristotle described sleep as “a seizure of the primary sense-organs, rendering [body] unable to actualize its power, arising of necessity[…]for the sake of its conservation.”
While the body doesn’t normally have seizures during sleep, Aristotle used the term “conservation,” as we now know sleep promotes mind and body restoration.
In 162 BCE, Galen identified the brain as the area of human consciousness rather than the heart— this paved the way for scientists to start learning about neuron communication in the body and, later, the stages our bodies go through to go to sleep.
For the next 1,500 years, sleep science made little progress. Sleep was considered a detoxifying process during which the body shut down because of a drop in temperature.
During the Middle Ages, people would go to bed two hours after dusk and wake up at midnight before returning to bed 1 to 3 hours later. Middle Age literature often refers to the segmented sleep periods as the first and second sleep.
Paris became the first city in the world to light its streets with wax candlelight in glass lamps. Three years later, Amsterdam lit its roads with oil-power lamps. London didn’t light its streets until 1684. By the end of the 1600s, 50 European cities had their streets lit at night. As a result, more people stayed up rather than turning in two hours after dusk.
Some cultures explored the idea of more comfortable sleeping arrangements.
During the Middle Ages, beds were a symbol of status. The poor and middle-class often slept on the floor or bags of straw. Wealthy merchants, upper classes, and royalty slept in bags filled with feathers and down placed on a bed frame.
Age of Enlightenment (1715 CE to 1789 CE)
In the Renaissance Era, rough cloth bag mattresses filled with straw or down were wrapped in silk cloth to provide a softer sleeping surface.
During the Enlightenment period, people started to interpret dreaming for themselves. Interpreting dreams is still a modern pastime, and while sleep scientists have resources dedicated to answering the question of “why do we dream,” experts have not found a definitive answer.
During the Enlightenment Period, sleep became regulated as more people became aware of the time sleep consumed when they could perform other tasks.
Industrial Revolution (1760 CE to 1840 CE)
“People were becoming increasingly time-conscious and sensitive to efficiency, certainly before the 19th Century,” says historian Roger Ekirch. “But the industrial revolution intensified that attitude by leaps and bounds.”
In the late 17th century, humanity began to turn from a farming economy to mass production and manufacturing. Artificial light (gas lamps, light bulbs, and street lights) and the spiking popularity of coffee houses created a demand for long workdays. Humans no longer had to abide by the sun’s schedule.
The manufacturing industry and artificial light also changed perception towards sleep. Segmented sleeping was compressed into a single sleep cycle and sleep was viewed as a waste of time. Those who hung onto biphasic sleeping were considered slothful and unable to keep up with the times.
In fact, Craig Koslofsky said, “Associations with night before the 17th Century were not good,” he says. “The night was a place populated by people of disrepute.” As a result, people who practiced segmented sleep routines were perceived to have criminal associations.
1900s to the Present
Our understanding of sleep and what it does began to make progress in the 1900s. One of the main discoveries allowing us to move forward was the discovery of neurons in 1888. Neurons are individual cells of the nervous system, which led to understanding how the brain communicated with the rest of the body and, later, how the brain induced sleep.
Since the industrial revolution affected human’s natural sleep schedule, most people were sleep-deprived. Barbital, a long-acting sedative and sleep-inducing drug, was invented in 1903 to help people get better sleep in shorter periods of time.
Sleep hygiene tip: While sleeping pills do help people get to sleep, they can cause the body to develop a dependency on them, which can make getting to sleep without them near to impossible. Instead of opting over-the-counter sleep aids, we suggest trying all-natural methods to get better sleep and consulting with your doctor.
Constantin von Economo, a neurologist and physician, studied patients with sleep abnormalities and identified the hypothalamus, a region in the brain responsible for the circadian clock.
In 1925, the electroencephalogram (EEG) was invented. The EEG detects electrical activity (brain waves) in the brain using small, metal discs attached to the scalp and led to the discovery that brain waves indicating wakefulness were different during sleep. This machine wasn’t available to the public until five years later.
Also in 1925, Nathaniel Kleitman, a distinguished sleep researcher, discovered REM (rapid eye movement) sleep. Afterward, Kleitman led studies on sleep and wakefulness, mental activity, consciousness, sleep disorders, and the effects of sleep deprivation.
In 1935, researcher Erwin Bunning discovered the biological clock and realized it resided in all living creatures.
Two years later, the team of Loomis, A. L., Harvey, E. N., & Hobart, G. A. discovered the five stages of sleep and named different characteristics of brain waves: delta, alpha, theta, beta, gamma. The discovery of the basic structure of sleep helped unravel many of the mysteries about sleep.
- Sleep Stage 1: Wakefulness
- Sleep Stage 2: NREM sleep 1
- Sleep Stage 3: NREM sleep 2
- Sleep Stage 4: NREM sleep 3
- Sleep Stage 5: REM sleep and dreaming
- Alpha: Brain is in a calm, relaxed state.
- Delta: These waves represent a loss of awareness when the brain is undergoing deep sleep.
- Theta: Brain waves that occur during REM sleep when the brain is in deep meditation and relaxation.
- Beta: The brain is actively concentrating, thinking, and processing information.
- Gamma: These waves indicate a higher mental activity where the person is awake, perceives objects, and problem solves.
In 1939, Kleitman published a book covering sleep disorders, temperature changes during sleep, sleep-wake cycles, and established the role the brain stem has in skeletal muscle relaxation during sleep, which advanced the neurophysiology of sleep.
In 1958, neurophysiologist Michel Jouvet made the distinction between REM and NREM (non-REM) sleep. Jouvet realized REM sleep was a stage of sleep accompanied by increased brain activity and skeletal muscle paralysis; meanwhile, NREM sleep is a state of low brain activity.
NREM and REM sleep are broken up into stages and each has varying sleep levels—you can wake up from some easier than others.
Stage 1 of NREM sleep: Occurs with sleep onset. In this state, you experience slow eye movement, and your body begins to relax and drop in temperature.
Stage 2 of NREM sleep: This is a deeper state of sleep, although you can still be woken with loud noises. During this stage of NREM sleep, you experience no eye movement, and your brain activity slows.
Stage 3 of NREM sleep: Characteristic of this stage are K complexes and sleep spindles in the EEG. Your muscles become paralyzed to prepare you for REM sleep and dreaming.
REM sleep: REM sleep and its accompanying dreams can last between 5 and 45 minutes A sleeper in REM sleep will not wake easily. Your eyes and muscles do not move during this stage; however, your brain is as active in REM sleep as it is when you are awake. It’s believed body paralysis prevents sleepers from acting out vivid images and sounds in their dreams.
In 1925, Dr. Nathaniel Kleitman opened the first sleep lab at the University of Chicago.
“The development of the electroencephalogram (EEG) in the 1930s, constituted the earliest effort to measure brain activity during sleep,” says Dr. Santhi. “This incredible technology allows us to observe changes in brain electrical activity in real time while someone is sleeping. Another technique that was developed to study sleep was prolonged sleep deprivation. This technique allowed scientists to gain valuable insights and knowledge about the importance of sleep in physiology and psychology.”
In 1953, Kleitman and his student Eugene Aserinsky discovered REM sleep.
In 1958, scientist Franz Halberg named the circadian rhythm, which is a physiological 24-hour cycle, dictating when the body feels tired, awake, and hungry. He studied these rhythms in human beings for the first time and became the father of chronobiology. The discovery of the circadian rhythm revolutionized how to diagnose sleep disorders.
In 1962, Jouvet discovered pons in the brainstem regulated REM sleep. During this time, obstructive sleep apnea became a well-known sleep disorder and led studies based on temperature, circulation, and breathing during sleep.
After the publication of the first sleep-dedicated, peer-reviewed medical journal in 1970, a sleep clinic and laboratory opened at Stanford University in 1972. By the 90s, over 200 American sleep labs and centers were treating sleep disorders.
In 1980, the connection between circadian rhythms and sleep duration was discovered, as well as the relationship between sleep and learning. The necessity of sleep for sustainable life was also discovered.
In the 90s, numerous sleep theories were proposed. It was discovered orexin receptor deficiency caused narcolepsy. Light and retinal pigment’s role in syncing the biological clock with the sun was uncovered, shedding light on the sleep regulation process.
Notable sleep researchers of the 80s and 90s include:
- Alex Borbeley (two process model of sleep)
- Charles Czeisler, Daan and Beersma on the role of light as a synchronizer of the circadian system,
- Allan Hobson
- William Dement
In 2001, Ekirch published a seminal paper based on 16 years of research revealing that humans used to sleep in two chunks. Four years later Ekirch, published a book, At Day’s Close: Night in Times Past, including over 500 references depicting segmented sleeping patterns.
In 2003, Giulio Tononi, MD, PhD, and Chiara Cirelli, MD, PhD, proposed the idea that sleep allowed the nervous system’s communication networks to increase and reduced energy levels to conserve strength. They learned sleep was needed to consolidate memory.
Scientists are still working to identify a principle of sleep causation on human life and work toward understanding genetic, environmental, and psychological aspects of sleep disorders.
Society and Sleep Today
Carl Jung, psychiatrist, psychoanalyst, and founder of analytical psychology, stated dreams are the pathway to the collective unconscious of all people. Scientists delved into the study of sleep afterward and disproved the theory that sleep was a waste of time.
Today, we know sleep plays a large role in memory consolidation, the ability to carry out tasks, creativity levels, cognitive thinking, and emotional stability. Sleep is tied to success, it seems.
We also know there is an enormous cost to sleep deprivation, including high-stress levels, anxiety, depression, and an increased risk of heart disease and diabetes. Lack of sleep can leave an individual with decreased cognitive capabilities equal to someone under a sedative’s influence. As such, it can enable false memories, low emotional intelligence, and a decrease in confidence and self-esteem.
Some industries have provided employee work schedules allowing frequent sleep opportunities: 6 hours on/6 hours off, 4 hours on/8 hours off, 8 hours on/8 hours off.
Split sleep/work schedules allow for multiple work and rest periods so sleep deprivation decreases and productivity increases. As long as the number of sleep hours amounts to 7 to 9 hours within 24-hours, split sleep patterns promote the same health benefits as a monophasic sleep schedule.
Despite our understanding of sleep, humans don’t spend more time sleeping than we did in the 1900s. In the early 1900s, people averaged 9 hours a night. In 1970, people reported closer to 7 hours per night. Today, one in three adults aren’t getting enough sleep due to stress and tasks demanded of them on a daily basis. While companies are offering work schedules allowing more sleep, we still need to make sleep a priority.
For a brief refresher, biphasic sleep or segmented sleep is the act of sleeping in two periods with a 1- to 3-hour intermission.
Biphasic sleep is the most natural sleep routine for humans, so some people may feel more rested following that schedule.
Psychologist Thomas Wehr conducted a study involving restricting light to 10 hours with 14 hours of darkness. After a 4-week adjustment period, the subjects reverted to a biphasic sleep routine adopted by our ancestors, involving a two-segmented sleep pattern broken up by 1 to 3 hours of wakefulness.
However, other people will sleep better in an eight-hour sleep schedule.
Today’s society can demand a monophasic sleep routine for an individual to get enough sleep and keep their lives running smoothly.
Advantages of Biphasic Sleep
Adopting a biphasic sleep schedule could allow modern society more flexibility.
It’s believed those with insomnia sleep better in a biphasic routine and it would be beneficial for them to give up a monophasic sleep routine.
Ekirch believed most sleeping disorders are rooted in human’s natural segmented sleep preference and influenced by the presence of artificial light—a condition called sleep maintenance insomnia.
Sleep maintenance insomnia appeared in literature in the 19th century as soon as segmented sleep was phased out of society. Sleep psychologist Gregg Jacobs says, “Waking up during the night is part of normal human physiology.”
Consolidating sleep into one period is making sleepers wake up anxious, which prohibits sleep and follows people into their waking lives. Russel Foster, a professor of circadian neuroscience at Oxford, says, “Many people wake up at night and panic…what they are experiencing is a throwback to the bi-modal sleep pattern.”
Foster said over 30 percent of medical issues doctors face are directly or indirectly linked sleep; the majority of medical doctors fail to acknowledge sleep problems relating to the monophasic sleep pattern.
Modern Latin American and European cultures adopted a biphasic sleep routine involving an extended rest period at night and a nap, allowing people a midday rest when energy declines.
Jacobs states the waking period between sleep regulated stress by forcing people into periods of rest, “It’s not a coincidence that, in modern life, the number of people who report anxiety, stress, and depression has gone up.”
Biphasic sleeping isn’t conducive to modern society as it doesn’t fit work-related and family obligations.
Some people’s lives allow them to adhere to the biphasic sleep schedule but may find themselves suffering daytime sleepiness—in which case they should conform to the monophasic sleep routine.
Frequently Asked Questions
Why do we sleep at night?
We sleep at night because sunlight inhibits melatonin production (the sleep hormone). With less melatonin in the body, we stay active and alter throughout the day. When the sunsets and we are exposed to less light, melatonin production increases, and we become tired and ready for sleep. If we didn’t sleep at night, the constant exposure to sunlight would stop melatonin production and make it difficult for us to fall asleep.
Why do we dream?
Dreams often occur during REM (rapid eye movement) sleep because this is when the brain is most active, but the body is in a state of paralysis, though dreams can also occur in NREM sleep. Sensory information and impressions from can the day come up during a dream.
Some experts believe we dream to learn how to deal with challenging situations, while others believe dreaming is simply a product of the memory consolidation taking place during REM sleep.
Does the body heal faster when sleeping?
During deep sleep, HCG hormones work to repair sore, damaged muscles. Your body also makes white blood cells during sleep, allowing the body to detect and fight bacteria and viruses that could make us sick. Rest gives the immune system the boost it needs to keep us healthy and strong.
What is the safe sleep position?
In most cases, back sleeping in the safest sleep positions. This position keeps body weight evenly distributed so the spine can rest in a safe, neutral position. If you frequently snore or have sleep apnea, an adjustable bed or a wedge pillow can open up the airways and make breathing more comfortable when back sleeping.
What happens if you don’t get REM sleep?
A lack of REM sleep can lead to memory loss, poor cognitive performance, and depression. Over time, serious health conditions, such as obesity, Type 2 Diabetes, dementia, and heart disease, can also occur. Some experts believe that a lack of REM can also cause migraine headaches.
Sleep is required to have a healthy life. Sleep disturbances caused by a sleep disorder, noise, artificial light, or a throwback to the biphasic sleep pattern can leave a sleeper with daytime sleepiness. If you’re having trouble sleeping or find yourself experiencing long sleep latency, you may consider visiting a sleep physician to correct any issues.