Why Do People Have To Sleep?

About one third of his life is spent in sleep. During this time, one is helpless and defenseless. But the night’s sleep is indispensable for body functions such as immune defense, healing and memory formation

Night after night, people dive into their second, enigmatic life. They cut off their connection to the outside world. Paralyzed, they lie there while their brains talk to themselves and revive bizarre images inside them. If sleep does not have an absolutely vital function, then it is the biggest mistake the evolutionary process has ever made. After all, humans and animals are never so vulnerable while sleeping.


The ability to sink into unconscious being has even increased in the course of evolution. In order to wake up a dormant person in his usual environment from deep sleep, it already requires a considerable effort. No living thing we know sleeps so deeply as a human. But why are we sleeping anyway?

Nocturnal energy saving mode for diurnal creatures

The source of the need may simply be that the earth sets the rhythm of most living things: day and night. Flowers open and close to the “sundial”, even some protozoa tick in their beat, are sometimes more active, sometimes less. In the animal kingdom, some adapted to the bright, warm day, others developed into creatures of the night.

For diurnal creatures such as humans, it made sense to retire at night from the predators, to remain motionless and switch to an energy-saving mode. But can that really be the cause of such an universal need? How strong this is, also show the tricky adjustments of some animals. Dolphins, for example, only ever sleep with one half of their brains. After all, they have to turn up in their sleep to catch their breath. Migratory birds are probably similar.

“Larks” and “owls”: remnants from prehistoric times

Even in human slumber there are still traces of prehistoric times. This is how many people feel that they are in a strange bed after the first night. The reason: The left hemisphere remains in a kind of deference, as researchers found in the US. The sleeper will wake up more easily. That has ensured our survival. Because in a strange place could threaten new dangers.

Differences in sleep behavior were once useful. When is snooze time, tells us an internal clock that ticks about every 24 hours. In some people, this is something before, in others. Chronobiologists like the Munich sleep researcher Professor Till Roenneberg speak of “larks” and “owls”. When people still slumbered in groups, one could always raise some alarm.

But whether with one half of the brain or with both: All animals have to sleep – from roundworms to whales – but for different lengths of time. While the small pocket mouse laps 20 hours of the day, the giraffe has enough with two hours. Man lies with his six to eight hours between the Asian elephant and the domestic pig.

Lack of sleep weakens the immune system

Saving energy is certainly not the main reason that we spend a third of our lives in the springs. If we do not sleep, we die. Of course, this was not proven experimentally. But many things speak for it. So, rats are known to be at the end of two sleepless weeks at the latest. Their immune system collapses, their body temperature goes crazy.

In humans, there is a hereditary disease in which those affected by severe sleep disorders are afflicted. After onset of symptoms, this familial insomnia always ends in death within a few months. Many die of pneumonia. The cause of death fits perfectly with what we know so far about sleep. Thus, as we slumber, our bodyguards reform. Even a party night weakens this measurable. Subjects who went through night after vaccination developed weaker protection.

During sleep, growth hormones are released, and damages are repaired. Wounds heal faster during sleep. People who suffer from chronic sleep deprivation are prone to high blood pressure, obesity, metabolic disorders and even become more likely to suffer from cancer. Our brain needs sleep to get rid of garbage. The interstices between the cells expand, harmful metabolic products that arise during the day, can be flushed out.

Sensory impressions end up in the long-term memory

But that does not explain why we lose consciousness in slumber. Memory researchers have been on the trail of the riddle for decades. During sleep, our memory is formed. Countless attempts have confirmed that. Especially in deep sleep, when our mind swings in long delta waves, memories become solid.

Sensory impressions that end up in the short-term memory of the brain during the day, in the hippocampus, are anchored in the long-term memory of the neocortex. It does not just copy content from one location to another. Memory education is a highly active process. New experiences are linked with old memories, the unimportant are sorted out. But why isn’t that also the case in the waking state?

To create long-term memory, the content in the temporary memory must be reactivated. Measurements of the brain waves make this visible. If at the same time sensory impressions flow in, this could lead to problems. The result could be hallucinations – as they often occur during long sleep deprivation. Learning while sleeping is not a myth. It is everyday life.

The learned is linked during sleep

But more happens. In one experiment, volunteers supplemented series of numbers. They did not know that there was a pattern in it. Those who recognized it quickly had the solution. After eight hours, the test subjects had to compete again. Some had slept, the others not. Of the sleepers, twice as many recognized the system. In sleep a kind of synopsis has to happen. So, sleeping through something can solve problems.

That we don’t unnecessarily oversleep our lives can be considered proven. Yet our society has a tense relationship with the dark third of our lives. We seem to be lying in the sheets without any sense of purpose, which does not contribute to our economic success. According to surveys, sleep disorders have long since become a widespread disease. Because even if we clock our lives perfectly: sleep does not come at the push of a button. The path in Morpheus’ arms leads only to a relaxed release – especially the will to control. If you absolutely want to sleep, stay awake.

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