From Cavefires to Smartphones: The Evolution of Human Sleep

This article traces humanity's fascinating journey in understanding sleep, from ancient civilizations to modern neuroscience, revealing how our knowledge of rest has transformed healthcare and human well-being.

By tracing the biological and evolutionary history of rest, it helps readers understand why our brains aren’t wired for blue-light screens and irregular schedules. It’s not just a lesson in sleep science; it’s a compelling argument for re-aligning with our ancestral cues to improve cognitive clarity, mood, and long-term health.

Takeaways

• Sleep evolved with humanity, shaped by nature and community, and its history holds answers to modern challenges.

• Industrialization and technology fractured natural sleep cycles, but modern science offers solutions.

• Ignoring sleep’s biological roots harms mental and physical health; prioritizing it is non-negotiable self-care.

• Minor adjustments and scientific breakthroughs can transform sleep quality.

  Reducing blue light at night, aligning with natural light, and adopting "sleep passports"

• Sleep isn’t passive—it’s active brain maintenance critical for lifelong health.

  
  

Introduction

Sleep isn’t just a biological process—it’s a story written into our DNA. Humans slept under the stars for millions of years, woke with sunlight, and shared rest with their tribes. Today, we battle screens, schedules, and stress, often treating sleep as an afterthought. But our bodies haven’t forgotten their roots.

In this article, I’ll walk you through the fascinating history of sleep, explain why modern habits clash with our biology, and share practical ways to align your life with what your brain and body genuinely need. Let’s rediscover sleep together.

As a neuroscientist studying sleep for over two decades, I've witnessed remarkable transformations in our understanding of this fundamental biological process.

Sleep in Early Humans—A Tribal Rhythm

Early humans didn’t track sleep with apps; they followed the sun. Tribes slept in shifts, with some members awake to guard against predators. Firelight extended evenings slightly, but darkness still dictated rest. Research shows their sleep cycles were biphasic—short naps paired with nighttime rest—adapting to seasonal light changes.

According to historical research, early European documents suggest that humans historically slept in two distinct periods, often referred to as "first sleep" and "second sleep," with a period of wakefulness in between. This indicates that humans may have evolved to sleep in two shifts before the widespread adoption of artificial light.

Why It Matters Today:

Our brains still expect darkness to trigger melatonin, the “sleep hormone.” Artificial light disrupts this, confusing our internal clocks. A 2023 study in Nature found that camping without electronics for 48 hours resets the circadian rhythms to align with the natural cycles of sunset and sunrise.

Ancient Beginnings: Sleep in Early Civilizations

When I examined ancient Egyptian medical papyri from around 1500 BCE, I was struck by their sophisticated approach to sleep. These early physicians documented various sleep disorders and prescribed treatments ranging from herbal remedies to sleep temples. The Egyptians viewed sleep as a state between life and death, a time when divine messages could be received.

Moving to ancient Greece, Hippocrates made the first recorded connections between sleep and health around 400 BCE. His observations about sleep patterns and their relationship to illness remain relevant to our modern understanding of sleep medicine.

Is napping good or bad?

Naps can boost alertness if kept under 30 minutes and before 3 PM. Longer naps risk grogginess and nighttime insomnia.

The Medieval Period: Sleep as a Medical Mystery

During the Middle Ages, sleep became intertwined with religious and supernatural beliefs. As a scientist, I find it fascinating how medieval physicians attempted to explain sleep through the four humors theory, where four bodily fluids—blood, yellow bile, black bile, and phlegm—determined a person's temperament. An imbalance led to certain sicknesses, dependent upon which humors were in excess or deficit.

The humors were associated with celestial bodies, seasons, body parts, and various stages of life. While their explanations weren't accurate, their systematic approach to understanding sleep laid the groundwork for future scientific inquiry—image source Wikipedia.

The Scientific Revolution: First Glimpses into Sleep's Nature

The 17th and 18th centuries brought the first scientific studies of sleep. In 1729, Jean-Jacques d'Ortous de Mairan conducted the first circadian rhythm experiment using plants, opening a new chapter in sleep research. This period marked our first understanding that sleep followed internal biological patterns.

Night in the early 18th century, as painted by William Hogarth. Photograph: Bridgeman Art Library

Factories introduced shift work, divorcing sleep from natural cycles. Gas lamps and later electric bulbs turned night into day. By the 1920s, the 8-hour sleep block became standard—but not necessarily natural. Studies now show this rigid schedule clashes with genetic differences in sleep needs.

The Modern Era: Sleep Science Takes Shape

The real breakthrough in sleep research came in 1924 when Hans Berger invented the electroencephalogram (EEG). I often tell my students that this moment was like suddenly being able to read the brain's diary. The EEG allowed us to observe different sleep stages and understand that sleep isn't a uniform state of unconsciousness.

Hans Berger (1873-1941) in 1 927, with the ‘ E lektrenkephalogramm’ of his daughter Ilse. Upper trace: Ilse in rest (alpha waves), middle trace: Ilse in calculating a sum (beta waves), and lower trace: Ilse in giving the outcome of the sum (mixed waves). Image source: Researchgate.

Does alcohol improve sleep?

Alcohol sedates but blocks REM sleep, leaving you less restored. Avoid it 3 hours before bed.

The Discovery of REM Sleep

One of my favorite stories in sleep research history is the 1953 discovery of REM sleep by Eugene Aserinsky and Nathaniel Kleitman. Their finding that our brains are highly active during certain sleep phases revolutionized our understanding of sleep's role in memory, learning, and emotional regulation.

Brain Science Simplified:

Think of your prefrontal cortex as a tired CEO. At night, it needs downtime to sort memories and emotions. Without it, decision-making and creativity suffer.

Modern Sleep Medicine: A New Frontier

Today, we use advanced technologies like fMRI, PET scans, and AI-powered sleep tracking to understand sleep better than ever before. Recent research has revealed sleep's key role in:

• Brain waste clearance through the glymphatic system

• Memory consolidation and learning

• Emotional regulation and mental health

• Immune system function

• Metabolic health

The Discovery of Sleep Stages

In the 1950s, researchers Eugene Aserinsky and Nathaniel Kleitman made a groundbreaking discovery - the existence of rapid eye movement (REM) sleep. This finding revolutionized our understanding of sleep architecture, classifying sleep into distinct stages.

The sleep cycle repeats several times throughout a single sleep period. During each cycle, time spent in each stage of sleep shifts. Infographic: Sleep Foundation

Can I ‘catch up’ on lost sleep?

Occasional weekend rest helps, but chronic debt harms health. Consistency beats binge-sleeping.

The Circadian Rhythm

Our sleep-wake cycle is governed by an internal biological clock known as the circadian rhythm. This rhythm is primarily controlled by a group of neurons in the brain called the suprachiasmatic nucleus. Understanding this rhythm has been fundamental in explaining why we feel sleepy at certain times and alert at others.

The Role of Adenosine

One of the key players in regulating sleep is a molecule called adenosine. As we stay awake, adenosine builds up in our brains, increasing our sleep pressure. This process helps explain why we feel tired the longer we stay awake.

Sleep and Mental Health

Recent research has highlighted the strong connection between sleep and mental health. A meta-analysis found that improving sleep quality led to significant improvements in various mental health outcomes, including depression, anxiety, and stress. This underscores the importance of prioritizing good sleep for overall well-being.

During sleep, the brain works to evaluate and remember thoughts and memories, and it appears that a lack of sleep is especially harmful to the consolidation of positive emotional content. This can influence mood and emotional reactivity and is tied to mental health disorders and their severity, including the risk of suicidal ideas or behaviors. Image source: Sleep Foundation.

The Latest Sleep Research Breakthroughs

Recent studies have transformed our understanding of sleep's impact on health. In my lab and others worldwide, we uncover new connections between sleep quality and various health outcomes. For instance, a 2023 advanced brain imaging study revealed how sleep helps form long-term memories by strengthening neural connections during specific sleep stages.

A 2024 paper in Sleep Medicine Reviews linked irregular work hours to a 30% higher risk of metabolic disorders. Meanwhile, the World Health Organization classifies night shifts as a probable carcinogen.

This chart reveals a trend in how our sleep patterns have changed over the past several decades. In 1960, people slept an average of about 8.2 hours per night. However, this duration has steadily declined, dropping to approximately 7.35 hours by 2024. The historical data shows a consistent downward trend through the decades, with particularly noticeable drops in the 1990s and 2000s.

Understanding Sleep Disorders

The recognition and treatment of sleep disorders have undergone evolution. In 1970, the first sleep clinic opened at Stanford University, marking a new era in sleep medicine. Today, we understand more than 80 different sleep disorders, from common conditions like insomnia to rare disorders like fatal familial insomnia.

Sleep Studies at BioLife Neuroscience Center

Over 80 different sleep disorders can disrupt your normal sleep patterns. Some of the most common sleep disorders include:

• Insomnia: Difficulty falling or staying asleep 

• Sleep apnea: A breathing disorder that causes you to stop breathing for at least 10 seconds while sleeping 

• Restless legs syndrome (RLS): A tingling or prickly sensation in your legs that makes you want to move them 

• Hypersomnia: Difficulty staying awake during the day 

• Narcolepsy: An inability to regulate when you fall asleep or how long you stay awake 

• Circadian rhythm disorders: Problems with your natural sleep-wake cycle that make it hard to fall or wake up at the times you need 

• Parasomnias: Unusual behaviors that occur while falling asleep, sleeping, or waking up, such as walking, talking, or eating in your sleep 

• REM sleep behavior disorder: Acting out your dreams while in the rapid eye movement (REM) stage of sleep 

Sleep disorders can be linked to medications or other health problems, and some can be life-threatening.

Technology and Sleep: A Double-Edged Sword

Modern technology has dramatically impacted our sleep patterns. While devices can disrupt our natural sleep cycles through blue light exposure, they enable unprecedented sleep-tracking capabilities. As a researcher, I've observed how these tools have revolutionized our ability to study sleep patterns in natural environments.

Modern Sleep Challenges—The Price of Hyperconnectivity

Smartphones bombard us with dopamine-triggering alerts, keeping our brains alert long past sunset. The average adult checks their phone 144 times daily—each ping delaying sleep onset. Teens today sleep 2 hours less than those in the 1980s, correlating with rising anxiety rates.

Since their release in 2007, smartphones and their use have seemingly become a fundamental aspect of life in Western society. Image source: New Scientist

A 2023 trial in JAMA Psychiatry found that limiting screen use after 8 PM reduced insomnia symptoms in 78% of participants within two weeks.

Action Step: Charge your phone outside the bedroom. Replace late-night scrolling with a book or calming music.

Add this to your sleep routine:

• Cooler Temps: Early humans slept in cool caves. A 65°F (18°C) room mimics this, aiding deep sleep.

• Community: Sharing sleep spaces (like families or partners) lowered nighttime anxiety.

• Natural Light: Morning sunlight boosts serotonin, which converts to melatonin at night.

Pro Tip: Try a “sleep passport”: 1 hour before bed, dim the lights, write tomorrow’s to-do list (to quiet mental chatter), and sip herbal tea.

The Future of Sleep Research

As technology advances, so does our ability to study sleep. Wearable devices now allow us to collect sleep data on a much larger scale. This wealth of information opens new avenues for research and personalized sleep interventions.

Final Thoughts

As we look to the future of sleep research, I'm optimistic about our growing ability to address sleep-related health challenges. The historical perspective teaches us that each discovery builds upon previous knowledge, leading to better sleep solutions for everyone.

Your relationship with sleep isn’t fixed. Small, consistent changes—like prioritizing morning light or a phone-free bedroom—add up. Start tonight. Your brain will thank you.

Frequently Asked Questions

1. How did ancient civilizations treat sleep disorders?

   Ancient civilizations primarily used herbal remedies, sleep temples, and lifestyle modifications. Egyptian medical papyri describe treatments using opium poppies and other natural sedatives, while Greeks emphasized diet and exercise for better sleep.

   
   

2. What was the most significant breakthrough in sleep research?

   The invention of the EEG in 1924 revolutionized sleep research by allowing scientists to observe brain activity during sleep. This led to the discovery of different sleep stages, transforming our understanding of sleep's complexity.

   
   

3. How has our understanding of dreaming evolved?

   Our knowledge of dreaming has progressed from supernatural interpretations to the scientific study of REM sleep and its functions. Modern research indicates that dreams play a role in emotional processing and memory consolidation.

   
   

4. What role did the Industrial Revolution play in changing sleep patterns?

   The Industrial Revolution significantly altered human sleep patterns by introducing artificial lighting and the adoption of shift work. This period marked a significant deviation from natural light-based sleep cycles in human history.

   
   

5. How has the COVID-19 pandemic influenced sleep research?

   The pandemic has accelerated sleep research, particularly in areas of stress-related sleep disorders and the impact of isolation on sleep patterns. It has also increased focus on home-based sleep monitoring technologies.

Sources:

Freeman, W. J. (2013). The discovery of EEG. In Electrical Brain Stimulation for the Treatment of Neurological Disorders (pp. 1-3). CRC Press.

Huberman, A. (2022). Master Your Sleep & Be More Alert When Awake. Huberman Lab Podcast. https://www.hubermanlab.com/episode/master-your-sleep-and-be-more-alert-when-awake

Huberman, A. (2023). An Active Model of Research Translation for the General Public. PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC10731552/

Scott, A. J., Webb, T. L., Martyn-St James, M., Rowse, G., & Weich, S. (2021). Improving sleep quality leads to better mental health: A meta-analysis of randomised controlled trials. Sleep Medicine Reviews, 60, 101556. https://pmc.ncbi.nlm.nih.gov/articles/PMC8651630/

Huberman, A. (2025). How to Defeat Jet Lag, Shift Work & Sleeplessness. Huberman Lab Podcast. https://www.hubermanlab.com/episode/find-your-temperature-minimum-to-defeat-jetlag-shift-work-and-sleeplessness

Huberman, A. (2024). Joe Rogan Experience #1958. YouTube. https://www.youtube.com/watch?v=xVvSe9xJoys

Merschel, M. (2024). New research provides fresh, large-scale look at who's coming up short on sleep. American Heart Association News. https://www.heart.org/en/news/2024/11/20/large-scale-look-at-whos-coming-up-short-on-sleep

Huberman, A. (n.d.). Sleep Hygiene. Huberman Lab. https://www.hubermanlab.com/topics/sleep-hygiene

Reddit. (2022). Without doubting his credentials, is Andrew Huberman's content legit? https://www.reddit.com/r/cogsci/comments/rwqr3p/without_doubting_his_credentials_is_andrew/

Chaput, J. P., Dutil, C., & Sampasa-Kanyinga, H. (2018). Sleeping hours: what is the ideal number and how does age impact this? Nature and Science of Sleep, 10, 421-430. https://pmc.ncbi.nlm.nih.gov/articles/PMC6267703/

---

About Dr. David L. Priede, MIS, PhD

As a healthcare professional and neuroscientist at BioLife Health Research Center, I am committed to catalyzing progress and fostering innovation. With a multifaceted background encompassing experiences in science, technology, healthcare, and education, I’ve consistently sought to challenge conventional boundaries and pioneer transformative solutions that address pressing challenges. Follow me on Linkedin.

Founder and Director of Biolife Health Center and a member of the American Medical Association, National Association for Healthcare Quality, Society for Neuroscience, and the American Brain Foundation.

Visit Biolife Health Research Center Health and Fitness Tech Reviews for a Healthier You.