We feel sleepy when it gets dark primarily because of the release of a hormone called melatonin in our bodies.
The Role of Melatonin
When darkness falls, our bodies naturally produce more melatonin. According to research, the sleep hormone melatonin is secreted in the body when it's dark. This increased melatonin levels signals to our brain that it's time to rest and prepare for sleep, leading to feelings of tiredness. We have higher levels of melatonin in our bodies when it's dark outside and for that reason, we become more tired.
Adaptability and Survival
Humans are adaptable creatures and this melatonin response is a key part of our circadian rhythm, which regulates our sleep-wake cycle. As stated in the reference, "We're adaptable and that's why we've been able to survive up here in the north." The reference indicates that humans can adapt to varying light conditions. This means our bodies are designed to respond to changes in light, promoting sleep when it's dark.
Factors Affecting Sleepiness
While darkness and melatonin are primary drivers, other factors can also contribute to feeling sleepy:
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Circadian Rhythm: Our internal clock is heavily influenced by light exposure.
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Lifestyle: Regular sleep schedules, diet, and exercise can all impact our sleepiness.
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Age: Sleep patterns and melatonin production change as we age.
The Impact of Artificial Light
The advent of artificial light has altered our natural sleep patterns. Exposure to screens and bright lights in the evening can suppress melatonin production, making it harder to fall asleep.
Understanding the Sleep-Wake Cycle
The table below summarizes the interplay between darkness, melatonin, and sleep:
| Condition | Melatonin Level | Feeling of Sleepiness |
|---|---|---|
| Darkness | Increased | Higher |
| Bright Light | Decreased | Lower |
