Study: Modern life returned sleep habits to ancient patterns

Researchers found temperature may be more important to sustaining sleep than thought.

By Stephen Feller

LOS ANGELES, Oct. 16 (UPI) -- Although theories persist that modern life -- work, technology, electricity -- has led to humans maintaining an unnatural sleep pattern, a new study of traditional populations suggests the idea is wrong.

Researchers at the University of California Los Angeles, working with the Hadza of Tanzania, the San of Namibia and the Tsimane of Bolivia, found the length of nightly sleep, when people go to sleep and wake up, and the commonality of naps now are more similar to human ancestral habits than people think.


"Rather than saying modern culture has interfered with the natural sleep period, this is a case in which modern culture, with its electric light and temperature control, was able to restore the natural sleep period, which is a single period in traditional humans today and therefore likely in our evolutionary ancestors as well," said Jerome Siegel, a professor of psychiatry at UCLA's Semel Institute of Neuroscience and Human Behavior, in a press release.

Siegel and the research team asked 94 members of the three groups to wear watch-sized devices that monitored their sleep patterns, body temperatures, temperature of their environments, and the amount of light they were exposed to.


The data showed participants didn't go to sleep with the sun, staying up for about 3 hours and 20 minutes after sunset. Once asleep, they racked up about six and a half hours of rest -- which researchers said is on the low end of adult averages in industrialized societies.

Participants in the study rarely took naps, but slept about an hour more during winter than during the summer. Once people fell asleep, they didn't wake up much, and if they woke, it was not for long.

Researchers note two of the groups do not have a word for insomnia, because they generally don't experience it. They theorize sleep temperature may be connected to this because although they usually woke up after temperatures have been dropping throughout the night, when it has gotten progressively colder, most people in industrialized nations sleep in temperature controlled environments.

"I feel a lot less insecure about my own sleep habits after having found the trends we see here," said Gandhi Yetish, a doctoral candidate at the University of New Mexico who spent 10 months with the Tsimane tribe during the study. "There's this expectation that we should all be sleeping eight or nine hours a night and that if you took away modern technology people would be sleeping more. But now for the first time we're showing that's not true."


The study is published in Current Biology.

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