Why Do We Sleep?

Sleep is seen as interrupting life, but the real scourge is chronic sleeplessness. In Japan, about 40 percent of the population sleeps less than six hours a night. A full night’s sleep now feels as rare and old-fashioned as a handwritten letter. We all seem to cut corners, fighting insomnia through sleeping pills, guzzling coffee to slap away yawns, ignoring the intricate journey we’re designed to take each evening.

Around 350 B.C., Aristotle wrote an essay, “On Sleep and Sleeplessness,” wondering just what we were doing and why. For the next 2,300 years, no one had a good answer. In 1924 German psychiatrist Hans Berger invented the electroencephalograph, which records electrical activity in the brain, and the study of sleep shifted from philosophy to science. It’s only in the past few decades, though, as imaging machines have allowed ever deeper glimpses of the brain’s inner workings, that we’ve approached a convincing answer to Aristotle.

Everything we’ve learned about sleep has emphasized its importance to our mental and physical health. Our sleep-wake pattern is a central feature of human biology—an adaptation to life on a spinning planet, with its endless wheel of day and night. The 2017 Nobel Prize in medicine was awarded to three scientists who, in the 1980s and 1990s, identified the molecular clock inside our cells that aims to keep us in sync with the sun. When this circadian rhythm breaks down, recent research has shown, we are at increased risk for illnesses such as diabetes, heart disease, and dementia.

There is further evidence that sleep is essential for maintaining a healthy immune system, body temperature, and blood pressure. Without enough of it, we can’t regulate our moods well or recover swiftly from injuries. Sleep may be more essential to us than food; animals will die of sleep deprivation before starvation, says Steven Lockley of Brigham and Women’s Hospital in Boston.

Yet an imbalance between lifestyle and sun cycle has become an epidemic. “It seems as if we are now living in a worldwide test of the negative consequences of sleep deprivation,” says Robert Stickgold, director of the Center for Sleep and Cognition at Harvard Medical School. The average American today sleeps less than seven hours a night, about two hours less than a century ago. This is chiefly due to the proliferation of electric lights, followed by televisions, computers, and smartphones. In our restless, floodlit society, we often think of sleep as an adversary, a state depriving us of productivity and play. Thomas Edison, who gave us light bulbs, said that “sleep is an absurdity, a bad habit.” He believed we’d eventually dispense with it entirely.

Insomnia is by far the most common problem, the main reason 4 percent of U.S. adults take sleeping pills in any given month. Insomniacs generally take longer to fall asleep, wake up for prolonged periods during the night, or both. If sleep is such a ubiquitous natural phenomenon, refined across the eons, you might wonder, why do so many of us have such trouble with it? Blame evolution; blame the modern world. Or blame the mismatch between the two.

Maybe, then, we’ve been asking the wrong question about sleep, ever since Aristotle. The real wonder isn’t why we sleep. It’s why, with such incredible tranquility available, do we bother to stay awake?

Abstracted from National Geographic magazine August 2018 edition.