On one level, our need for sleep seems simple. We feel tired, we sleep, we wake up, and we feel better.
On another level, though, there are still a lot of questions. Why do we get tired? Why can’t we just keep going and going and going until we die? Wouldn’t we get a lot more done and get a lot more out of life if we didn’t have to sleep? Why do we need it, anyway?
Functional Theories of Why We Sleep
On one level, it’s pretty easy to figure out why we sleep. When we rest, our bodies regenerate themselves. Our cells repair themselves, our muscles repair any damage or small tears that have taken place and they grow as appropriate. The body releases growth hormone and regulates those levels. We also synthesize proteins.
Most of these processes also happen while we’re awake, though at a much lower, slower level. However, there are a few things that only happen in the body when we’re asleep. Clearly, then, we sleep because our bodies need to fix themselves.
In addition, we sleep so that we can rest and conserve energy. Both the heart and the lungs work significantly less when we’re asleep than they do while we’re awake. They get a chance to rest so that they will last longer and work better when they have to work hard. If we didn’t sleep, we would have to eat a lot more, because our metabolic rates are also lower when we’re sleeping.
On this functional level, it’s clear that our bodies need the rest we get when we sleep. Without sleep, they would fall apart much faster.
Brain Theories of Why We Sleep
Other theorists look to changes in the brain to explain why we need to sleep. They claim that these are the real reason behind sleep, with the body simply taking advantage of the state to get some work done, too.
When we sleep, our brains become more able to perform complex tasks and learn new things. You only have to think about how hard it is for people to drive when they’re sleepy for this to make sense! And think about the last time you had to take a test, write a paper, or perform a complex task at work when you were tired. Being sleepy makes it almost impossible.
We need sleep to regulate our moods, too. People who don’t sleep well are more likely to be depressed and anxious, and to be unable to process emotions the way they usually do.
Finally, the brain uses the time we’re asleep to clear out toxins that build up during normal chemical reactions during the day. The waste-flushing system in the brain, called the glymphatic system, is almost 10 times more active when we’re asleep. Our brain cells also shrink, so that this system can work more efficiently and flush more toxins out. Since these toxins are believed to contribute to conditions like Alzheimer’s disease, sleep is clearly key for the brain.
Even if we don’t yet understand why these things all happen, the fact that we know that so many different brain functions improve with sleep is enough for some theorists. The brain is our most important and complex organ. If it needs sleep, then that must be why we sleep.
Abstract Theories of Why We Sleep
Some theorists reject both the body and the brain theories of why we sleep, preferring instead a more abstract reason. They believe that sleep developed for some other reason and that both the brain and the body learned how to use it for their own purposes.
One of the more prominent of these theories goes back to evolution. This theory states that animals who slept were quiet and still at night, and so were more likely to survive than animals that were wide awake all night. The sleeping animals would be more likely to avoid attacks by predators and accidents in the dark, both of which might befall animals who wandered around and didn’t sleep.
Over time, this theory states, sleep was so much safer than being awake that all animals slept. Parents who slept passed on the genes and the skills of sleep to their children, permitting them to survive as well. This went on for millions of years until every animal (and, eventually, every human) slept.
There are many theories as to why animals and people need to sleep. While we may never know, for sure, why we sleep, we can definitely say that it’s important. With all that sleep does for our brains and the rest of our bodies, it’s worth it to get as much good sleep as we possibly can. Learning to get enough sleep can be hard, but having a body that functions well is absolutely worth it.