Why Do We Sleep?

Sleep is both a need and a ritual.

Illustration of a human and several animals sleeping
Natalie Andrewson

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Why do living things sleep? “Ask researchers this question, and listen as, like clockwork, a sense of awe and frustration creeps into their voices,” Veronique Greenwood wrote in 2018.

“In a way, it’s startling how universal sleep is,” she continued. “In the midst of the hurried scramble for survival, across eons of bloodshed and death and flight, uncountable millions of living things have laid themselves down for a nice, long bout of unconsciousness. This hardly seems conducive to living to fight another day … That such a risky habit is so common, and so persistent, suggests that whatever is happening is of the utmost importance.”

In other words, Greenwood writes, “whatever sleep gives to the sleeper is worth tempting death over and over again, for a lifetime.” Whatever sleep gives us is also worth the many hours, and large amounts of money, that humans now spend figuring out how to maximize our slumber. Sixty percent of America’s adults report experiencing sleep problems every night or most nights, Amanda Mull noted in 2019, and a variety of industries have sprung up to help us sleep longer and better.

Sleep is a need, but it’s also a ritual: Where we sleep, when we sleep, and who we sleep next to say a lot about who we are and what we want. Today’s reading list explores sleep as a scientific mystery, a physical need, and the most consistent routine of our daily lives.

On Sleep

A medieval knight sleeping
Hulton Archive / Getty

Can Medieval Sleeping Habits Fix America’s Insomnia?

By Derek Thompson

“My 3-a.m. awakenings aren’t an unnatural disorder but an ancestral echo.”

The Atlantic

Why Everyone Should Sleep Alone

By Malika Rao

On the virtues of splitting up for the night

A child sleeping next to a dog
Keystone View / FPG / Getty

I Found the Key to the Kingdom of Sleep

By Amanda Mull

It’s my foot.

Still Curious?

Other Diversions


I’ll leave you with one sleep fact from the animal kingdom that only adds to the mystery: Golden hamsters “have been observed waking up from bouts of hibernation—in order to nap,” Greenwood reports. “Whatever they’re getting from sleep, it’s not available to them while they’re hibernating.” But what is it? Scientists still don’t know.

— Isabel