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People who live without artificial light do not sleep more than about 6.5 hours a night.

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Hunters and gatherers awoke BEFORE sunrise. 

Here’s the story that people like to tell about the way we sleep: Back in the day, we got more of it. Our eyes would shut when it got dark. We’d wake up for a few hours during the night instead of snoozing for a single long block. And we’d nap during the day.

Then—minor key!—modernity ruined everything. Our busy working lives put an end to afternoon naps, while lightbulbs, TV screens, and smartphones shortened our natural slumber and made it more continuous.

All of this is wrong, according to Jerome Siegel at the University of California, Los Angeles. Much like the Paleo diet, it’s based on unsubstantiated assumptions about how humans used to live.

Siegel’s team has shown that people who live traditional lifestyles in Namibia, Tanzania, and Bolivia don’t fit with any of these common notions about pre-industrial dozing. “People like to complain that modern life is ruining sleep, but they’re just saying: Kids today!” says Siegel. “It’s a perennial complaint but you need data to know if it’s true.”


Even if Siegel is right, that doesn’t mean that our sleeping patterns have been unaffected by modern lifestyles. After all, his team found that insomnia, a common affliction of Western society, is almost non-existent in the three groups. Neither the San nor Tsimane even have a word for insomnia in their language. Why?

His study provides three clues. First, all three groups wake up before sunrise, in stark contrast to Westerners who typically rouse when it’s already light. Once up, the volunteers got the most light exposure at around 9 a.m.; in the middle of the day, when the sun is at its strongest, they head for shade. Siegel thinks this might explain why people with seasonal affective disorder respond well to bright light, especially in the early morning. “It seems like more than a coincidence that this is when all these groups are getting their maximal light exposure,” he says. “We have lost this exposure by living indoors the way we do.”

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