Along with the paleo diet, that dubious collection of advice supposedly based on what our cave-people ancestors ate, we've now got paleo sleep. (Google it if you must.) Setting aside paleo sleep's questionable provenance, however, one might wonder: How did our ancestors sleep?
Probably a lot like us, according to a new study of contemporary hunter-gatherer societies. And whatever differences that might exist could help doctors better treat sleep disorders like insomnia.
Americans are certainly getting less sleep than ever. According to a recent Gallup poll, adults in the United States get, on average, 6.8 hours of sleep per night, which is about an hour less than they did in 1942. This can have potentially serious consequences—sleep disorders are associated with obesity, heart disease, and high blood pressure, among other things. And while there are myriad reasons for our lack of sleep, the rise of the Internet and cell phones is certainly a prominent contributor. A 2011 National Sleep Foundation study, for example, found that people who regularly texted or surfed the Web in bed were more likely to report getting a good night's rest, but were also more likely to feel sleepy during the day.
"Sleep in industrial societies has not been reduced below a level that is normal for most of our species' evolutionary history."
In other words, modern society might be to blame for us getting fewer hours of sleep. If that's true, it suggests less industrialized societies ought to get more sleep. At the least, we ought to be able to learn something from studying the sleep habits of, say, modern-day hunter-gatherers.
And that's exactly what Gandhi Yetish, Jerome Siegel, and a team of anthropologists and sleep researchers did. They focused on four societies that still live (or until recently lived) the hunter-gatherer lifestyle: the Hadza of Tanzania; the Kalahari and Ju/'hoansi San in Namibia; and the Tsimane of Bolivia. The scientists outfitted adults with activity monitors to track their sleep, as well as temperature and humidity, over periods of six to 28 days in summer and winter.
"In these societies, electricity and its associated lighting and entertainment distractions are absent, as are cooling and heating systems," the researchers write today in Current Biology. Nevertheless, Hadza, San, and Tsimane adults slept six to seven hours a night on average, usually going to bed several hours after sundown, and waking up a bit before dawn—just as people in industrialized societies do.
"Our findings indicate that sleep in industrial societies has not been reduced below a level that is normal for most of our species' evolutionary history," the team writes.
But there were differences to us modern folk, who hit the hay when we're bored with Netflix and awaken to jarring alarm clocks. Hunter-gatherers, by contrast, seem to time things according to temperature—they fall asleep as temperatures drop post-sunset and re-awaken at the coldest part of the day, just before dawn. Re-creating those sorts of conditions in modern bedrooms, the authors write, "might have beneficial effects on sleep and insomnia in industrial populations."
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