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Sleep is one of the oddest things that animals do. It has managed to confuse scientists ever since scientists have been thinking about it. From a basic perspective you can understand why an organism needs to rest and recoup, but why does it need to drift into an unconscious state for a third of its entire life? Deep sleep gives “mates” ample opportunity to do something “funny” to you whilst you’re out for the count.

Everyone knows that you can skip a whole night’s sleep if you have to, but we also know that you’ll feel proper shady until you catch up with your kip. Sleep must be vital to life otherwise it wouldn’t have evolved at all.

It makes sense that sleep benefits us by allowing our bones and muscles to rest and our organs are given time to repair, but why do we have to be unconscious and unaware? Couldn’t we just lie really still for a bit?

Curling up unconscious in a hole for 7 hours means you are hyper-vulnerable to predation, you are literally a sitting duck, or mouse or human. Whatever’s going on must be 100% vital otherwise nature would never have expected us to put ourselves at such risk.

In an attempt to minimise the amount of time they’re out for the count some animals, like dolphins and whales, have developed the ability to sleep with just one side of their brain at a time – unihemispheric sleep – this means they are always at least half alert. But most animals aren’t as lucky as the dolphins, it’s all or nothing.

Different animals need different amounts, for instance, a giraffe only takes about 30 minutes of deep sleep throughout a day, whereas a brown bat will grab as much as 20 hours sleep given half a chance.

Most baby animals need considerably more sleep than an adult, which is a clue to just how important it must be. Although having said that, dolphins and orcas don’t sleep at all for the first few months of life. Amphibians rest, but it is unclear as to whether they go into full sleep, as defined by their neural activity, but insects, including the common fruit fly, do have sleep patterns similar to animals. Everyone’s at it.

So sleep is all-pervasive but varies greatly from critter to critter. It’s clearly essential, but it’s been a tricky task to work out why. The best way to test why we need something is to stop someone having it and see what happens. Sleep deprivation studies have been done of course, and if an animal is deprived of sleep indefinitely it will eventually die. But then, keeping a rat awake isn’t just depriving it of sleep, it’s also stressing it out to the max via electric shocks.

There certainly have been some pretty hairy negative effects found due to sleep deprivation in humans though.

Sleep deprivation studies on humans have found the following list of symptoms which are likely to occur if someone isn’t sleeping enough over a long period of time. They vary from unsurprising to quite worrying:

• aching muscles
• confusion, memory lapses or loss
• depression
• development of false memory
• hallucinations
• hand tremor
• headaches
• malaise
• stye
• periorbital puffiness, commonly known as “bags under eyes”
• increased blood pressure
• increased stress hormone levels
• increased risk of diabetes
• increased risk of fibromyalgia
• irritability
• nystagmus (rapid involuntary rhythmic eye movement)
• obesity
• seizures
• temper tantrums in children
• yawning
• mania
• symptoms similar to ADHD and psychosis

We can all remember seeing a few of those symptoms in ourselves after a couple of heavy weekends back-to-back. But what could cause such a myriad of symptoms?

Despite knowing some of the benefits of having sleep and some of the negative impacts of not having sleep, it has only been very recently that an actual physical pathway has been found that causes some of these things.

Charles Czeisler, a sleep researcher at Harvard Medical School in Boston, told Science Magazine’s Emily Underwood that this new research shows the “first direct experimental evidence at the molecular level” for why we need to sleep.

All of our cells produce waste as they work, this cellular goop would kill cells if it weren’t cleared away, so the lymphatic system sweeps it up as we go. The brain, however, is locked behind the blood-brain barrier and therefore can not be cleaned up by the same lymphatic action. Toxic proteins, the sort that produce Alzheimers and other beefs, build up in the fluid inside and around the brain.

Charles Czeisler and his team have, for the first time, proven that sleep is essential for the brain to be able to clear up this toxic buildup once a day as we sleep. When we get some shut-eye the channels between individual cells grow, this increase in space around the cells allows the brain and spinal fluid to wash in the gaps and flush out the build up of, well, basically, cell poop.

This might seem like a pretty small step forwards, and I guess it is. But all of science is tiny steps forward. Each problem needs a bunch of baby steps before we can all stride across it. This is a small key to a small lock in a massive problem and who knows where it might lead next?

Lord knows there are still enough weird questions about the human body that we need to answer.