Why Do We Sleep During The Night And Not During The Day?

Sleep is a fundamental human need, and we spend roughly one-third of our lives doing it.

However, have you ever wondered why we sleep during the night and not during the day?

While it may seem like a simple question, the answer is rooted in the complexities of our biology, evolution, and culture.

In this blog post, we'll explore the science behind our sleep patterns and delve into the social and cultural factors that shape them.

Circadian Rhythm

Our body's internal clock, also known as the circadian rhythm, is a complex biological process that regulates many physiological processes in our bodies, including our sleep-wake cycle.

The circadian rhythm is a 24-hour cycle that is driven by our exposure to light and darkness.

It is controlled by an area of the brain called the suprachiasmatic nucleus (SCN), which is located in the hypothalamus.

The SCN is responsible for regulating our sleep-wake cycle by sending signals to other areas of the brain that control the release of certain hormones, including melatonin.

Melatonin is a hormone that is released by the pineal gland in the brain in response to darkness, and it helps to regulate our sleep-wake cycle.

When melatonin levels are high, we feel sleepy, and when they are low, we feel awake and alert.

How it affects sleep patterns

The circadian rhythm plays a crucial role in regulating our sleep patterns.

It determines when we feel naturally awake and when we feel naturally sleepy.

This is why most people feel awake and alert during the day and sleepy at night.

When our circadian rhythm is disrupted, it can cause problems with our sleep patterns.

For example, people who work night shifts or have jet lag may have difficulty falling asleep or staying asleep because their circadian rhythm is out of sync with their external environment.

Similarly, people who regularly stay up late and sleep in on the weekends may also experience disruptions to their circadian rhythm, which can lead to sleep problems.

Importance of regulating circadian rhythm

Regulating our circadian rhythm is crucial for our overall health and well-being.

Studies have shown that disruptions to the circadian rhythm can lead to a variety of health problems, including metabolic disorders, cardiovascular disease, and mood disorders.

Additionally, a lack of sleep or poor sleep quality can have negative effects on our physical and mental health, including impaired cognitive function and increased risk of accidents.

To regulate our circadian rhythm, it's important to maintain a consistent sleep schedule, expose ourselves to bright light in the morning, and avoid bright light in the evening.

For example, we can try to go to bed and wake up at the same time every day, even on weekends.

We can also try to get exposure to natural light during the day and avoid exposure to bright screens in the evening, as the blue light emitted by screens can disrupt our circadian rhythm.

By making these adjustments, we can help ensure that our bodies stay in sync with the external environment and promote healthy sleep patterns.


Melatonin is a hormone that is produced by the pineal gland in the brain.

It is released in response to darkness and helps to regulate our sleep-wake cycle.

The production of melatonin is regulated by the circadian rhythm, which is controlled by the suprachiasmatic nucleus (SCN) in the hypothalamus of the brain.

When it gets dark outside, the SCN signals the pineal gland to release melatonin, which helps to promote sleep.

Melatonin levels in the body typically begin to rise in the evening, when it starts to get dark, and peak during the night.

In the morning, as it gets lighter, melatonin levels decrease, signaling to our bodies that it's time to wake up.

Melatonin levels can also be affected by age, with older adults producing less melatonin than younger adults.

How it affects sleep patterns

Melatonin plays a critical role in regulating our sleep patterns.

It helps to promote sleep by reducing alertness and increasing drowsiness.

Melatonin is often referred to as the “hormone of darkness” because it is released in response to darkness and helps to promote sleep during the night.

Research has shown that melatonin supplementation can be helpful in regulating sleep patterns in people with insomnia, jet lag, or other sleep disorders.

However, it's important to note that melatonin is not a cure-all for sleep problems and should only be used under the guidance of a healthcare professional.

How light exposure impacts melatonin levels

Light exposure plays a crucial role in regulating melatonin levels in the body.

Light exposure, especially blue light emitted by electronic devices, can suppress the release of melatonin, making it more difficult to fall asleep and stay asleep.

Exposure to bright light during the day, especially in the morning, can help regulate our circadian rhythm and promote healthy sleep patterns.

On the other hand, exposure to bright light in the evening, especially from electronic devices, can disrupt our circadian rhythm and suppress the release of melatonin, making it harder to fall asleep.

One way to limit the impact of light on melatonin levels is to establish a regular sleep schedule and stick to it, even on weekends.

This can help regulate the circadian rhythm and promote healthy sleep patterns.

Another way to limit light exposure in the evening is to avoid using electronic devices, such as smartphones or tablets, before bedtime.

Additionally, using tools such as blue light filters or wearing amber-tinted glasses in the evening can help reduce the impact of light on melatonin levels and promote healthy sleep.

Evolutionary Perspective

Our sleep patterns are not just influenced by our biology and environment, but also by our evolutionary history.

Sleep is a fundamental aspect of animal behavior, and different species have evolved to sleep in different ways.

In this section, we will explore the evolutionary perspective of human sleep patterns, looking at theories on why we evolved to sleep at night and how our sleep patterns compare to those of other animals.

Theories on why humans evolved to sleep at night

One theory for why humans evolved to sleep at night is based on the idea that it was a way to avoid predators.

Sleeping during the day would have made early humans more vulnerable to predators, whereas sleeping at night provided a measure of protection.

Another theory is that sleeping at night was a way to conserve energy.

Early humans may have needed to be active during the day to hunt and gather food, so sleeping at night would have allowed them to conserve energy for those activities.

Comparison of humans and other animals' sleep patterns

Humans are not the only animals that sleep at night.

Many other mammals, such as cats, dogs, and primates, also sleep at night.

However, there are also many animals that sleep during the day, such as rodents and some primates.

The amount of sleep animals need and the way they sleep can also vary widely.

For example, some animals, such as dolphins, only sleep with one half of their brain at a time, while others, such as sloths, can sleep for up to 15 hours a day.

By comparing human sleep patterns to those of other animals, we can gain a better understanding of the evolutionary history and function of sleep.

Social and Cultural Factors

While our sleep patterns are largely influenced by our biology and environment, social and cultural factors also play a significant role in shaping our sleep habits.

From historical sleep patterns to modern-day cultural norms around sleep, these factors can have a significant impact on our sleep quality and quantity.

In this section, we will explore the social and cultural factors that influence our sleep patterns, including the historical context of sleep, and modern-day cultural norms around sleep.

Historical context of sleep patterns

Sleep patterns have varied widely throughout history, reflecting changes in cultural and societal norms.

For example, in pre-industrial societies, it was common for people to sleep in two separate phases, with a period of wakefulness in the middle of the night.

This pattern of “segmented sleep” was seen as natural and normal, and people would use the period of wakefulness to pray, read, or socialize.

The Industrial Revolution and the rise of artificial lighting changed sleep patterns significantly, as people began to work longer hours and stay up later at night.

The development of shift work and other non-traditional work schedules has also contributed to changes in sleep patterns over time.

Modern-day cultural norms around sleep

Modern-day cultural norms around sleep vary widely across different societies and cultures.

In some cultures, sleep is viewed as a luxury, while in others it is seen as a necessity.

The amount of sleep that people get also varies widely, with some societies promoting a “work hard, play hard” mentality that values staying up late and getting up early, while others prioritize sleep and rest.

Technological advances have also had an impact on our sleep habits, with many people using electronic devices late into the night, which can disrupt sleep patterns.

By exploring the historical and cultural context of sleep patterns, we can gain a better understanding of how social and cultural factors shape our sleep habits, and how we can work to promote healthy sleep in our modern-day lives.


In conclusion, sleep is a fundamental human need that is influenced by a variety of factors, including biology, environment, and social and cultural factors.

From the role of the circadian rhythm and melatonin in regulating sleep patterns, to the impact of historical and cultural norms on our sleep habits, our understanding of sleep is constantly evolving.

By recognizing the importance of healthy sleep and taking steps to promote healthy sleep habits, we can improve our physical and mental well-being, and enjoy the many benefits that come with a good night's sleep.