The concept of sleep
Sleep is a fundamental and mysterious aspect of life. While most people recognize its importance, sleep’s underlying mechanisms and reasons are still being studied. So far, based on the results of the studies, sleep scientists have come to the conclusion that sleep is closely related to physiological functions and brain activity.
Moreover, it has been observed that sleep plays a crucial role in memory consolidation, allowing individuals to process and retain new information. Additionally, sleep helps regulate emotions and stress levels, contributing to overall mental well-being. Research also suggests that sleep enhances creativity and problem-solving skills essential for daily functioning. Without adequate sleep, individuals may experience difficulty concentrating and making decisions, leading to decreased productivity and cognitive performance.
What is sleep?
Sleep occurs in multiple stages, one of which involves heightened brain activity. Throughout the night, people transition through cycles of deep sleep and dreaming. Interestingly, most individuals do not remember what happens while they are asleep, making sleep an almost unconscious experience. The body undergoes crucial biological processes during sleep, including tissue repair and the release of growth hormones. Additionally, sleep plays a role in maintaining emotional balance and psychological resilience.
All living organisms exhibit sleep-like behaviors, though their sleep patterns and methods of rest vary (Harvard Medical School, 2021). Scientists have identified key characteristics of sleep by analyzing changes in responsiveness and behavior. Understanding these patterns helps researchers study sleep disorders and their effects on health. By examining various species, scientists have gained insights into the evolutionary significance of sleep.
- Sleep reduces reactivity to external stimuli. During sleep, sensory perception decreases, making it harder to wake up due to minor noises or disturbances. This reduced responsiveness allows the body and brain to rest without constant interruptions from the environment.
- It minimizes bodily movement. The body experiences muscle relaxation during sleep, reducing unnecessary energy expenditure. This lack of movement helps prevent injury and allows the body to focus on restorative functions like muscle recovery and immune support.
- Sleep is often associated with a specific posture. Different species have adapted unique sleeping positions to maximize comfort and safety. For example, humans typically sleep lying down, while certain animals, like horses, can sleep while standing to remain alert to predators.
- Brain wave patterns change significantly during sleep. Sleep is characterized by distinct stages, each marked by different brain wave activity. Rapid eye movement (REM) sleep, for instance, is associated with vivid dreams and heightened brain activity, while deep sleep promotes physical restoration and memory consolidation. (Harvard Medical School, 2021)
Why do people need to sleep? The science behind sleep
Like all living organisms, humans have adapted to Earth’s cycle of day and night. Research suggests that sleeping at night helps people conserve energy, avoid predators, and recover physically. The circadian rhythm is an internal biological clock that regulates sleep and wakefulness in sync with the day-night cycle. This rhythm is influenced by external cues, such as light and temperature, which signal the body when to rest and when to be alert. Disruptions to the circadian rhythm, such as jet lag or shift work, can negatively impact sleep quality and overall health. Studies have shown that people who maintain a consistent sleep schedule tend to have better cognitive function and emotional stability.
According to Bryan and Peters (2022), every evening, the body releases melatonin, a hormone that promotes sleep. As daylight appears, melatonin levels decrease, allowing individuals to wake up naturally. This cycle ensures proper rest and cognitive function. Melatonin production is affected by exposure to artificial light, especially blue light from screens, which can delay sleep onset and reduce sleep quality. Researchers recommend limiting screen time before bed and maintaining a dark sleeping environment to support natural melatonin production. Additionally, other hormones, such as cortisol, also follow a daily rhythm, rising in the morning to promote wakefulness and decreasing at night to aid relaxation.
Why do animals need to sleep?
As stated by Chmary (2023), there are three main theories explaining why animals need sleep:
- Physical Restoration—Sleep aids in detoxification and bodily recovery by eliminating waste and generating essential molecules. During sleep, the body repairs damaged tissues strengthens the immune system and replenishes vital proteins needed for growth and healing. This process is particularly important for animals that engage in high levels of physical activity, such as migratory birds or hunting predators.
- Cognitive Benefits—Sleeping enhances brain function, helping to organize and strengthen neural connections, which improves learning and memory. Studies show that animals who experience sleep deprivation struggle with basic survival tasks, such as finding food or recognizing threats. Furthermore, adequate sleep is essential for young animals, as their brains develop rapidly and require rest to process new experiences and stimuli.
- Energy Conservation—Sleep allows animals to balance their energy reserves, which is crucial for survival, especially for predators and foragers. Many species have evolved sleep patterns that align with their feeding habits; for example, carnivores tend to sleep longer since they consume high-energy meals, while herbivores sleep less to remain vigilant against predators. Some animals, like bears, even enter hibernation as an extreme form of energy conservation.
Animals that don’t fully sleep
Some animals have evolved unique sleep adaptations to survive in their environments. The following creatures exhibit unusual sleep patterns:
Dolphins
Dolphins possess a special sleep mechanism called unihemispheric sleep, which allows one half of their brain to rest while the other remains alert. This adaptation enables them to continue swimming, monitor their surroundings, and breathe. Additionally, newborn dolphins do not sleep for their first month, staying active to bond with their mothers and avoid predators (Times of India, 2024).
Fruit Flies
Fruit flies, despite their short lifespans, have circadian rhythms similar to humans. Some fruit flies can survive with minimal rest, while others can function without sleep altogether (Times of India, 2024).
Giraffes
Giraffes sleep for only a few minutes at a time, totaling around 30 minutes to two hours per day. Their short sleep cycles help them remain alert to predators and maintain their towering stance, which is crucial for survival in the wild.
Sharks
Some shark species must keep moving constantly to pass water over their gills for oxygen. Instead of traditional sleep, they experience periods of rest while continuing to swim, allowing them to maintain essential bodily functions.
Elephants
Wild elephants sleep only about two to four hours per day, often standing up. Their large size and constant need to forage for food contribute to their limited sleep duration. Additionally, elephants may take short naps while walking.
The effects of sleep deprivation on life
Sleep deprivation has a significant impact on both mental and physical well-being. According to Newsom and Singh (2023), the following are some of the most common symptoms associated with a lack of sleep:
The first major effect is mood instability. Since sleep plays a crucial role in regulating emotions, inadequate rest can cause heightened irritability, stress, and mood swings. Individuals who experience prolonged sleep deprivation are at a greater risk of developing anxiety and depression. The inability to manage emotions effectively can also lead to conflicts in personal and professional relationships, further affecting overall mental well-being.
The second effect is cognitive impairment. Insufficient sleep reduces alertness, making it harder to focus and complete everyday tasks efficiently. Sleep-deprived individuals often struggle with multitasking, problem-solving, and decision-making. Additionally, studies suggest that sleep deprivation slows reaction times, which can be especially dangerous in activities requiring high concentration, such as driving or operating machinery. Over time, chronic sleep deprivation may even contribute to memory loss and diminished learning capabilities.
Another significant consequence is a weakened immune system. Sleep is essential for producing infection-fighting antibodies and cytokines, which help the body defend itself against illnesses. Without enough rest, the body becomes more susceptible to infections, such as the common cold and flu. Long-term sleep deprivation has also been linked to an increased risk of chronic conditions like heart disease and diabetes and weakened inflammatory responses, making overall recovery from illnesses slower.
Conclusion
So, how much sleep is considered optimal for different age groups? According to Newsom and Singh (2023), the recommended sleep duration varies depending on age. Infants aged 4–12 months should get 12 to 16 hours of sleep, including naps, to support their rapid growth and brain development. Toddlers aged 1–2 years need 11 to 14 hours, while preschoolers aged 3–5 years require 10 to 13 hours of rest to maintain their energy levels and support learning. School-aged children (6–12 years) should aim for 9 to 12 hours of sleep, whereas adolescents (13–18 years) need 8 to 10 hours to aid in cognitive and emotional development. Finally, adults aged 18 and older should get at least 7 hours of sleep per night for optimal health, reducing the risk of chronic illnesses and improving daily functioning.
Although these sleep guidelines provide a general framework, individual sleep needs can vary significantly from person to person. Factors such as lifestyle, stress levels, and genetics can influence how much rest someone requires to function properly, making it essential to listen to one’s body. Additionally, a person’s sleep duration may temporarily increase when recovering from an illness or after engaging in intense physical or mental activity, as the body needs extra time to repair and recharge. Consistently prioritizing quality sleep is essential for maintaining overall well-being, cognitive performance, and emotional stability, ultimately leading to a healthier and more productive life.
Bryan, L. and Peters, B., 2022. Why Do We Need sleep? [online] Sleep Foundation. Available at: https://www.sleepfoundation.org/how-sleep-works/why-do-we-need-sleep [Accessed 15 February 2025].
Chmary, J., 2023. What is sleep and why do animals need to sleep? [online] www.discoverwildlife.com. Available at: https://www.discoverwildlife.com/animal-facts/what-is-sleep [Accessed 15 February 2025].
Harvard Medical School., 2021. Science of Sleep: What is Sleep? [online] Harvard.edu. Available at: https://sleep.hms.harvard.edu/education-training/public-education/sleep-and-health-education-program/sleep-health-education-47 [Accessed 15 February. 2025].
Newsom, R. and Singh, A., 2023. Effects of Sleep Deprivation. [online] Sleep Foundation. Available at: https://www.sleepfoundation.org/sleep-deprivation/effects-of-sleep-deprivation [Accessed 15 February 2025].
TIMESOFINDIA.COM., 2024. 10 animals that don’t sleep and how. [online] The Times of India. Available at: https://timesofindia.indiatimes.com/etimes/trending/10-animals-that-dont-sleep-and-how/photostory/107883236.cms?picid=107883258vv [Accessed 15 February 2025].
