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According to the principles of evolution -

The only conclusion to come to is that the benefits of sleep have outweighed the risk of the animal being caught by a predator while being unconscious.

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There's a lot understood, too -

Although there is much about sleep that isn’t understood by science, there is a lot that we do understand. Sleep is linked with memory processing, emotional stability, and the brain’s rinse cycle.

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Have we evolved to only carry out certain processes during sleep? -

What we don’t know is whether these kinds of processes can only be carried out during sleep.

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If we never evolved to sleep -

There is no evidence to disprove that the body has just evolved to carry out these kinds of processes during sleep because it’s more efficient than during the day.

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Circadian rhythms -

The earth’s rhythm affects the circadian rhythms of almost all animals. This even applies to blind fish that live underground.

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Fatal familial insomnia -

There is an extremely rare disease called fatal familial insomnia, where at around middle age many members of the family experience strange symptoms like sweating, tremors, and insomnia.

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Fatal familial insomnia -

The disease is caused by a genetic mutation that causes a buildup of protein in the brain, damaging the thalamus, which controls our switch between wake and sleep.

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Sufferers rarely live longer than a year -

Sleeping becomes virtually impossible. Without sleep, sufferers of fatal familial insomnia fall into a kind of waking coma. From the onset of symptoms, they rarely live longer than a year.

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Why no sleep kills people is a mystery -

While there are many theories as to why human beings need sleep, there is no solid evidence suggesting why it would kill you if you don't sleep.

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To survive, we need sleep -

The fact is, however, that humans, and most other animals, need to be asleep for a good portion of their lives to survive, despite nobody knowing why.

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Rodents die in trials of organ ulcers and other complications -

What happens in any rodent study where they are sleep deprived for a long time is that they die. They develop ulcers on their organs, and they cannot regulate temperature. Eventually, they die.

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The shrinking sleeping brain -

Researchers discovered that cells in the brains of sleeping mice shrink, allowing liquid to pass and clean debris that builds up around cells during the day.

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Toxins build up -

Perhaps sleep is vital because, without it, these toxin by-products build up in the brain. However, it’s been proven that the human brain can also do it when a person is awake.

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The longest someone stayed awake and healthy -

The longest ever healthy wakeful person on record stayed awake for 11 days. By the end, his health began to decline, suffering mood swings, declining cognitive functions, and even hallucinations.

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The result -

Even with this, he recovered within a day or two and didn’t have any long-term health issues following it.

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Microsleep -

It turns out that sleep-deprived humans experience microsleeps, where parts of the brain can go to sleep while the person is awake.

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The big questions -

So, can sleep deprivation alone kill a healthy person? To what extent can the brain carry out these recoveries with microsleeps? The answers to these questions are also unknown.

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Memory processing and dreams -

Dreaming has been fascinating scientists for as long as science has existed, and one consensus in the community is that dreaming helps to process memories.

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The rat's maze -

After rats learn a maze, during their sleep the same parts of their brain light up in activity, indicating that they’re reliving it (i.e. they’re processing it). 

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Another paradox -

However, it could be that dreams are just a by-product of sleep that serves no function, like a tab left open on a computer until the screen goes to sleep. When people’s REM sleep is suppressed by certain drugs and they don’t dream, they don’t seem to experience any negative effects.

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Dreams as insignificant -

If the people who aren’t experiencing dreams don’t experience any negative effects, then there is no reason to believe that they are important, let alone significant to the life of a person, their relationships, and their career, for example.

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Sleeping rhythms -

Many people wake at 7 am ready for the day, while others have to drag themselves from their bed much later, stumbling towards the coffee pot.

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Genes and routines -

While Dr. Sam Jones was researching sleep at the University of Exeter, he found that almost 300 genes play a role in making you a morning or evening person.

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Routines are mostly environmental and habitual -

However true this is, it’s still understood to be more of a habitual and environmental part of our lives.

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Night owls' high risk of depression -

Night owls are at greater risk of many illnesses and, on average, have a lower sense of well-being and are more likely to develop depression. There is no clear reason as to why this is the case.

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A speculation -

Dr. Jones has speculated that since it’s not down to something obvious like sunlight hours, it could simply be down to night owls trying to fit in with a society set up for early birds.

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Recap -

Technological advances allow labs to watch how the brain is affected when someone's sleep is reduced. It's useful and interesting, but only shows us how we sleep, not why. However, it is clear that if we don't sleep well and for long enough, our health, well-being, and everything else in our lives are likely to decline.

Sources: (Science Focus) (Insider)

See also: The effects and health risks of sleeping too much

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