By: Stephanie Wright

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Did you know that every species of animal and even some plants sleep? Sleep is essential for most living things to function and maintain a good state of health. 

How human beings sleep has changed with time. Our bodies and brain have adapted over the years in response to how our environment has changed. 

Evolution may give us better insight into why sleeping patterns have adjusted and how our body is affected as we sleep and age. 

How has evolution affected sleep patterns?

Before answering this question, let’s first explore why we sleep. Sleep is needed for us to function mentally and physically. Yet, how we sleep has changed or evolved over time. 

Experts are still debating why we sleep the way we do and why it has shifted. Two theories look at possible restorative vs. adaptive reasons.

Let’s dive into each a bit further.

Restorative

This theory centers on the idea that during sleep, our body recuperates by doing one or more of the following:

  • resting
  • repairing
  • processing what we learned
  • dreaming
  • improving our immune system
  • avoiding tiredness
  • detoxifying

Others argue against this theory because even plants and simple forms of life sleep, which don’t participate in learning. Also, do dandelions need to dream?

More research is needed to be sure this theory is accurate.

Adaptive

Another idea is that we’ve adapted our sleep to meet the needs of our environment. As humans, we’ve evolved to become active in the day.

Our bodies need to develop and function to either fit daytime or nighttime, but we can’t do both. If we try, we wouldn’t be able to perform well in either. 

Take a look at nocturnal animals. Many of their eyes are structurally different than non-nocturnal animals and humans because their species has evolved to function at night. 

Essentially, when the first living things existed, their environment forced them to pick “day or night.” As a result, humans evolved to function in daylight so we might perform at our best for at least part of the day.

Simply put, we sleep at night because we cannot function to our full capacity day and night.

Sleeping fewer hours but more deeply

Today, we sleep fewer hours per day than earlier humans, but it’s a deeper sleep.

To survive, early humans felt pressure to sleep in the shortest possible time, leading them never to experience less quality sleep. Then, they needed to be more active for extended periods, such as evading predators and hunting for food, than those in modern times. 

Back then, humans lacked REM sleep as a result. Studies suggest REM sleep helps:

  • process memories
  • improve learning
  • enhance brain development
  • cell repair
  • boost creativity

Today, we sleep a deeper sleep which helps enhance our cognitive abilities and could be why our intelligence has grown so much over the years. 

Evolution and the internal body clock

An internal body clock regulates the sleep/wake cycle, known as our circadian rhythm. It tells us when we should be awake and sleep. 

The clock reacts to the sun going down by telling the body rest is needed so we might remain active and accomplish daily tasks. But, humans can function day and night by modifying their sleep patterns to meet specific needs.

Everyone has a unique circadian rhythm. For example, some people function on only a few hours of sleep per night with naps during the day, while others sleep more than ten hours. 

Factors that affect our internal body clock include:

  • artificial lighting
  • shift-work
  • faster international travel
  • caffeine and other stimulants

These and other factors help trick our circadian rhythms into staying awake when needed. 

Before the modern age, it probably was a lot more challenging to alter our sleep schedule or face sleep deprivation. 

How age affects sleep through history

Experiencing disruptions in sleep is a sign of aging. Research says when you reach around the age of 50, you can expect to start experiencing some of the following:

  • Falling asleep and waking up earlier. You’ll probably go to bed at an earlier bedtime while rising earlier, too.
  • Tossing and turning more. You might find falling asleep a bit more challenging with age.
  • Sleeping less. Even though you’re going to bed earlier, your sleep quality might lessen.
  • Experiencing more sleep disruption. You might awake more, become easily aroused, and experience lighter stages of sleep. 

Sleep disorders, especially sleep apnea and anxiety-related insomnia, appear more prominent today than years ago. This suggests one’s environment, diet, and support system may impact sleep. 

Experts can’t know how older adults slept hundreds of years ago. But, we could assume the rate of sleep disorders is higher today based on the factors mentioned affecting sleep. 

Evolution, sleep, and body temperature

When we sleep, our core body temperature drops. Studies suggest the body cools to:

Our circadian rhythms control our body heat. For example, when we “nest” or prepare for sleep, it influences body temperature, and thus sleep. 

In earlier times, before brick and mortar homes, air conditioning, and heating units, humans might not have achieved as deep of a sleep as we do today. The reason being is they had fewer opportunities to take shelter from the elements. 

Experts explain that warming up before sleep, such as a hot bath or warm blankets, may allow you to sleep faster and deeper. 

How to optimize your sleep based on how we evolved

Being well-rested is essential to stay in good health, regardless of age. Some great ways to get more Zzzs include:

  • Keep your bedroom dark, calm, quiet, relaxing, and cool. According to the Centers for Disease Control and Prevention (CDC), a temperature of 65 degrees is recommended for your room to achieve the best rest. 
  • Turn off artificial light sources like cell phones, televisions, and lamps. When you stop stimulating your brain, it allows your body to better prepare to sleep. 
  • Focus on eating a healthy diet and getting some physical activity during the day. Factors such as excess weight and heart disease may affect your sleep, so it’s helpful to prioritize your overall wellness to maximize your sleep quality.
  • Set a bedtime routine. Humans thrive on routine, so taking a shower or reading each night helps mold your circadian rhythm to fit your needs.

Resources

Harding E, et al. (2020). Sleep and thermoregulation. https://www.sciencedirect.com/science/article/pii/S2468867319301804

Mander B, et al. Sleep and human aging. (2018). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5810920/

Nunn C, et al. (2016). Shining evolutionary light on human sleep and sleep disorders. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4972941/

Peever J, et al. (2017). The biology of REM sleep. https://www.cell.com/current-biology/fulltext/S0960-9822(17)31329-5?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982217313295%3Fshowall%3Dtrue

Reddy S, et al. (2022). Physiology, circadian rhythm. https://www.ncbi.nlm.nih.gov/books/NBK519507/

Sleep for a good cause. (2022). https://www.cdc.gov/diabetes/library/features/diabetes-sleep.html

Samson D, et al. (2015). Sleep intensity and the evolution of human cognition. https://pubmed.ncbi.nlm.nih.gov/26662946/