What could you accomplish with eight more hours added to your day? Many of us could be more productive at work, enjoy more leisure activities — even spend more time with loved ones. Sleep takes up an astounding one-third of our lives. In days gone by, time was even more critical, as humans struggled to meet even their basic needs on a day-to-day basis. In addition, the need to sleep left us at a higher risk of being harmed by predators or rivals.

Despite the obvious reasons to eschew sleep, the indisputable fact remains: All humans need sleep. But why did we evolve to sleep for such a huge portion of our lives? New research may have answers for this age-old query.

Why Do We Sleep?

All living things have an internal 24-hour circadian rhythm that puts them in sync with the world around them. In animals, part of this circadian rhythm involves the need for sleep. Humans are diurnal animals, meaning that we naturally sleep for most of the night and are awake for most of the day.

According to new research, sleep may be essential because of its effect on our brain cells. As we function throughout the day, our brain cells create a large amount of metabolic waste. This, in turn, can damage DNA and other structures in our neurons.

In a recent study, researchers examined brain activity in zebrafish, which have a circadian rhythm surprisingly similar to humans. What they found was groundbreaking. When we sleep, different areas of our brains become quiet. This allows the cells to perform basic maintenance, flushing out waste products and repairing damage.

The authors of this recent study compared brain activity during sleep to repairing potholes. As we use roads, they accumulate damage. Without repairing this damage, the roads would eventually become unusable. Although there are many benefits to sleep, the basic need for slumber appears to be due to the need for neurons to repair themselves after the damage of the day.

What Happens When We Stay Awake All Night?

Lead study author Professor Lior Applebaum notes that “Despite the risk of reduced awareness to the environment, animals — ranging from jellyfish to zebrafish to humans — have to sleep to allow their neurons to perform efficient DNA maintenance, and this is possibly the reason why sleep has evolved and is so conserved in the animal kingdom.”

Even short-term accumulation of this damage can have noticeable negative effects on how we function. This can be seen in people who cut back on sleep for even a short period of time. When we don’t sleep well for even one night, we suffer from decreased alertness and impaired memory. There is also an increased risk of accidents, which can be deadly.

Our ancestors slept, putting themselves at risk from predators and other environmental risks, because skipping sleep left them in even greater danger. They could feel the negative effects that come with insomnia and lack of sufficient sleep, just as we all can in modern times. However, we now know that there are even greater long-term risks to skimping on sleep.

The Health Benefits of Sleep

Regardless of the reason behind our need for sleep, we definitely fare better when we are getting enough of it. In addition, sleeping during dark hours rather than during the day appears to be critical to our overall health.

Sleep is essential for cardiovascular health, particularly due to its role in helping to prevent atherosclerosis. Atherosclerosis is a precursor to heart disease and stroke, so protecting against this hardening and narrowing of our arteries is critical to lifelong well-being. This is likely due to the same cell maintenance activities seen in our brains; the repair of tissues and DNA while we slumber.

In addition, sleep is important for the immune system. When we do not get enough sleep, we are at a higher risk of developing a serious infection as our immune system struggles to fight off the germs in our environment. Several studies suggest that people who do not get enough sleep are also at higher risk of developing autoimmune diseases such as lupus and multiple sclerosis, in which our immune cells attack our own tissues.

Tips for Getting a Healthy Amount of Sleep

Several studies have shown that humans need seven to nine hours of sleep for optimal health. Getting this amount of sleep was likely a challenge for our earliest ancestors, who struggled to find safe and comfortable places to settle in for the night. It remains a challenge in a modern world of 24/7 lights and just as constant stress.

Good sleep hygiene is one of the most effective approaches to fighting insomnia and other sleep disorders. Go to bed and get up at the same time every day. Turn off all lights and screens around an hour before bed, instead choosing calming activities such as meditation in a dimly lit room. For many people, taking a melatonin supplement before bedtime can help to support a restful night of sleep.

Modern people may not need to worry about fighting off lions at night, but we still have sleep challenges. As with our caveman ancestors, our daily function and even our lifelong well-being depend on keeping a healthy circadian rhythm.