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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

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

Keystone View / FPG / Getty

I Found the Key to the Kingdom of Sleep

By Amanda Mull

It’s my foot.

Still Curious?

The lie we tell ourselves about going to bed early: Revenge bedtime procrastination seems illogical, but many of us still do it, Arthur Brooks writes. A physician’s guide to sleep in a stressful age: In 2017, James Hamblin weighed in on how much sleep we need, whether melatonin works, and other common sleep questions.

Other Diversions

You don’t know how bad the pizza box is. People’s choice: wildlife photographer of the year 2022 The truth about dentistry (From 2019)

P.S.

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