Why Do We Sleep?

Sleep is one activity that everyone engages in every night, and yet it remains something of a mystery. Do you have any theories on why it is we sleep?

It is obvious that our sleep schedule is tied to the day/night pattern. It certainly isn’t a coincidence that due to the earth’s rotation, it is dark every night, and we sleep every night.

Moreover, it seems pretty clear that sleep is the product of evolutionary pressures. Our very distant ancestors gained some advantage from being asleep every night that allowed them to survive, and possibly even to thrive.

However, we don’t know what that advantage is.

One possibility is that our senses leave us at a disadvantage to other predators in the dark. Our eyes do not allow us to see as well in the nighttime, nor do our ears hear so well as to make up the difference, compared to some of our animal competitors. Therefore, a survival mechanism is to keep humans inactive during the time when they are disadvantaged — at night — and concentrate their efforts in the daytime.

But why didn’t the eyes or ears evolve to be more sensitive? Other animals did, so why the difference in humans?

Another possibility is that our larger brains required more organization, and processing of information. For humans, this happens during the sleep cycle, in particular during REM sleep. This, in turn, requires long stretches of uninterrupted sleep, and that is easier at night with fewer distractions.

These are just two examples of possible explanations. Do you know of any others, or have a pet theory? In your opinion, why do we sleep?

Related questions: How many hours of sleep do you need? Do you have trouble sleeping? Early bird or night owl?

3 thoughts on “Why Do We Sleep?”

  1. Many years ago, I prided myself on only needing four to five hours of sleep each night. I justified it, saying I needed extra time to study for my college courses. On top of that, being a college activist to address hunger and homelessness issues in my community required coming up with detailed task lists and planning for organizing meetings with my fellow activists.

    I didn’t connect the fact depriving myself of sleep likely led to me getting sick more often. And it created times when I felt like a zombie. I’d also often crash on weekends. Cramming work into the work and class week may have felt like a time optimizer, but zoning out on weekends was time I could have shifted to a healthier study, work, and activism schedule.

    I’m much more health-conscious now. Suffering from depression and anxiety, I also read a lot about healthy brain function. Adequate sleep is necessary for a healthy life. This is what the National Institute of Health has to say about the matter:

    “Sleep is important to a number of brain functions, including how nerve cells (neurons) communicate with each other. In fact, your brain and body stay remarkably active while you sleep. Recent findings suggest that sleep plays a housekeeping role that removes toxins in your brain that build up while you are awake.

    Everyone needs sleep, but its biological purpose remains a mystery. Sleep affects almost every type of tissue and system in the body – from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. Research shows that a chronic lack of sleep, or getting poor quality sleep, increases the risk of disorders including high blood pressure, cardiovascular disease, diabetes, depression, and obesity.”

    Now, I try to get in eight hours of sleep each night. However, my body and mental health issues don’t always let this happen. Anxiety interrupts my sleep quite often. But all I can do is try.

  2. If I don’t get at least 4 1/2 hours of sleep per night I am physically and mentally unable to function somewhat normally the next day.
    My mind and body require a rest period to reset. Much like your computer needs to reset after a period of time or it slows down and doesn’t function properly.

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