Every vertebrate animal on the planet Earth must sleep. Sleep behaviors developed exceedingly early in evolutionary history; though different animals have developed different sleep patterns — with some animals sleeping with half a brain at a time, sleeping in 30-second increments or sleeping for almost the entire day — sleep is clearly an essential aspect of high-order life.
Yet, we don’t yet truly understand why.
Scientists in different fields have developed a variety of theories as to why humans need to sleep, but none have reached a definitive consensus. Here is an explanation of why sleep is so difficult for us to understand as well as a few leading ideas as to why sleep is so important.
The Trouble With Sleep
Sleep is difficult to study for several reasons. First, it is impossible for sleep researchers to use animal models in the pursuit of understanding more about human sleep because every species has developed unique sleep habits and patterns. Some birds will take micro-naps as they fly, and elephants can get by on just about three hours of sleep per night; in contrast, mice, the typical animal tool for research, require about 14 hours of sleep throughout the day. To understand human sleep, we can only study humans — and that poses problems, too.
Sleep researchers often equate sleeping to eating, as both are powerful internal drives. When a body is low on nutrients and needs energy, it generates the uncomfortable feeling of hunger to drive an individual to seek and consume food. Likewise, when a body is in need of rest, it generates the experience of sleepiness, compelling an individual to take a snooze. Yet, while almost everyone needs an identical ratio and quantity of nutrients from their food, different people can maintain vastly different sleep schedules and continue to thrive. Most people strive to sleep for a consolidated eight hours during the night, but some can happily get by on less while others need additional naps throughout the day to feel alert and well.
Unfortunately, many people suffer from sleep disorders that can interfere with their ability to develop restful patterns. A large number of people require substances to experience drowsiness or to remain asleep for hours at a time. Though natural sleep aids like hemp and melatonin are ideal, many sleepers rely on potentially dangerous concoctions, like cough medicine, allergy medicine, alcohol and even illicit drugs. Some people also suffer from physical conditions that make sleep more difficult, perhaps by causing pain or blocking airways in certain body positions. Until researchers can identify and isolate all such variables, human sleep will continue to be difficult to study.
Sleep research has not been a waste of time. We understand more about healthy human sleep pattens, to include the cycles of REM, light and deep sleep required for a person to achieve a rested feeling. We also understand how the body changes its functions during periods of sleep, such as slowing the heart rate and releasing specific hormones. Still, researchers are unable to point to a clear answer as to why so many living things must make themselves vulnerable and endure sleep — but they do have a few ideas.
Leading Sleep Theories
Inactivity Theory
One of the earliest explanations for the purpose of sleep, the inactivity theory suggests that sleep allows animals to remain still and quiet for extended periods, often during times when they are most vulnerable to attack. Yet, researchers have largely disproved this theory with evidence that remaining conscious is safer in that it provides an animal more time to react in an emergency. Thus, the unconsciousness caused by sleep can be a liability that should have been eliminated generations ago if sleep were not otherwise beneficial.
Energy Conservation Theory
In the wild, competition for energy resources is steep. Sleep radically reduces energy metabolism, allowing animals to consume less energy for an extended period of time and decreasing their energy needs overall. Thus, sleep may have developed as a means of conserving energy during periods when it would be least effective to search for food.
Restorative Theories
Some of the most well-known theories as to the purpose of sleep concern the body’s effort to restore, repair and rejuvenate itself. In truth, the body is constantly working to keep itself healthy, but some of the most important functions, such as those concerning the immune and nervous systems, can only occur when the body is asleep. Still, if this is the only purpose of sleep, it is a wonder that no vertebrate animal has evolved to perform these functions during waking hours.
Brain Plasticity Theory
One of the latest theories concerning sleep, the brain plasticity theory suggests that sleep allows the brain to alter its organization and structure for superior cognitive functioning. This theory is well-supported by evidence in children, who tend to require more sleep than human adults because their brains are experiencing greater changes as a result of growth and development.
By no means are we done researching the fascinating and fundamental phenomenon that is sleep. With enhanced tools and continued effort, we could unlock the secrets of sleep in the coming years.
Also Read: 5 Unique Treatments to Improve Your Sleep Cycle This Gloomy Season
