There’s a lot more to sleep than meets the eye. Sure, it looks easy and it’s more-or-less easy to do, but there’s still a lot we don’t yet know about sleep. Scientists are studying it all the time, and we are learning more and more.

However, we still don’t have a definitive answer to one of the most basic questions: Why do we need to sleep?

We Do Need Sleep

One of the things that research has shown over and over is that human beings don’t function well without sleep. When we don’t get enough of it, we suffer. Our brains don’t work as well. We can’t regulate our moods like we usually can. We feel hungry all the time, and we crave food that isn’t good for us. Our metabolisms slow, our hearts don’t work as well, we aren’t as strong or as fast, our sex-drive disappears, and we are more likely to get sick.

It’s pretty clear that enough sleep is an absolute necessity if we have any chance of thriving as human beings. But why do we need sleep so much? What goes on while we sleep that is so important to nearly every bodily system?

Theories About Why We Sleep

Over the years, scientists and other theorists have come up with many ideas for why we sleep. Some of the more interesting are developed below.

Evolution and Sleep



One interesting theory relies on evolutionary success to explain why we sleep. Theorists who ascribe to this theory believe that we sleep because, back in the evolutionary chain, creatures who slept were out of harm’s way during the dangerous nighttime hours.

Think about it: nighttime had to be dangerous for prehistoric man and for other diurnal creatures. Predators would be out and no one would be able to see them coming. It would be easy for accidents to happen, too, since creatures who were awake and moving around wouldn’t be able to see as well as they would during the day. Thus, creatures who hunkered down and were quiet at night would be more likely to survive and would pass this trait on to their children.

Physical Restoration and Sleep

There is evidence that the body repairs itself while we sleep. Our tissues repair themselves, our muscles grow, we make proteins, and we release growth hormones during sleep. Some of these things only happen while we sleep.

In addition, creatures that are completely deprived of sleep lose immune function entirely, usually dying within a matter of only a few weeks.

Some theorists point to these results and say that this rejuvenation isn’t coincidental but is, in fact, the very reason that we sleep. We sleep because that’s when the body can rest, fight disease, and restore itself.

Brain Growth and Sleep

Sleep is essential for the growing brains of babies and young children. Babies spend an inordinate amount of time asleep, and much of that is in REM sleep when they’re dreaming. As we get older, we spend less and less time in REM. It seems that this sort of sleep is somehow necessary to the brain producing enough neurons, culling the ones that it doesn’t need or want, and allowing it to develop as it should.

While we can’t deprive babies of sleep in the name of research, all we have to do is look at the effects of sleep deprivation on older people to get a clue as to what REM sleep offers. People who are sleep deprived struggle to learn new tasks, and they even struggle to perform their current ones with their usual ease. Just look at how hard it is for people to drive when they’re tired! Clearly, sleep does something for the human brain that cannot be achieved without rest.


We may not know exactly why people sleep, but we do know that it’s necessary. Research continues on the topic for a few reasons. First, figuring out why we were meant to sleep may help us learn to sleep better. Since sleep deprivation is running rampant in the world right now, this research promises to help a lot of people.

Studying why we sleep may also help us figure out how to counteract the effects of sleep deprivation. For instance, if we find that cell rejuvenation is one of the key reasons why we sleep, we may be able to determine which chemical reactions are involved in that process. If we can produce these in a different way, then we won’t have to depend on sleep so much.

In the end, though, studying why we sleep is fascinating. If you think about it, the fact that we spend nearly one-third of our lives unconscious is a little weird. It’s natural that we want to know why we do this.

by: Sarah Winfrey