Our Ancestors Probably Didn’t Get 8 Hours of Sleep a Night


A new study gives a glimpse at the sleep habits of pre-industrial humans. (Photo: Getty Images)

“Get seven to eight hours of sleep a night!” — it’s health advice we’ve all heard, and sure enough, lots of studies have shown the benefits of doing so.

But turns out, our ancient ancestors may not have even gotten this much sleep a night, new study suggests.

For a little more than three years, researchers from UCLA analyzed the sleep habits of 94 people living the pre-industrial hunter-gatherer lifestyle (meaning their day-to-day closely resembles that of our evolutionary ancestors): the Hadza people living near Serengeti National Park in Tanzania, the Tsimane people living along the Andean foothills in Bolivia, and the San people in the South African Kalahari Desert.

Participants in the study wore watch-sized devices that measured their sleep and wake times and light exposure; researchers also tracked how long and when these adults slept during the summer and winter, their body temperatures, and the temperature of their environments.

Among the findings:

  • They sleep 6.4 hours on average.

  • They do not nap regularly and do not awaken during the night.

  • They sleep an hour more in the winter than they do in the summer. They do not go to sleep when it gets dark—sleep onset is 3.3 hours after sunset, on average.

  • Their health is “excellent” and they have better levels of fitness than typical Americans of the same age.

  • The daily cycle of temperature change, which has largely been eliminated from modern sleep environments, may be a natural regulator of duration and timing of sleep.

Related: Your Body After a Night of Not-Enough Sleep

“Some have supposed that all our ancestors got nine, 10, or 11 hours of sleep—that we slept throughout the dark period. This is clearly incorrect,” lead study author Jerome Siegel, professor of psychiatry at UCLA’s Semel Institute of Neuroscience and Human Behavior, tells Yahoo Health. “The argument has always been that modern life has reduced our sleep time below the amount our ancestors got, but our data indicates that this is a myth.”

Another interesting discovery: Insomnia was rare for those in the study group. Meanwhile, nearly 30 percent of Americans suffer from this sleep disorder, according to the American Academy of Sleep Medicine. So were stress levels — which is linked to insomnia — taken into consideration?

“The problem is that we think that only modern humans are stressed and that our ancestors lived in a kind of Garden of Eden,” says Siegel. “Stress is normal and healthy — up to a point. In fact, the adults we studied were in better overall health than the average adult in contemporary society. They have lower levels of blood pressure, little atherosclerosis, and are not obese.”

Siegel emphasizes that those constantly deprived of shut-eye could be damaging their health. “But people who naturally sleep less than seven hours and have no daytime sleepiness or related problems should not think that they need to meet some arbitrary number of hours of sleep because it is the ‘natural" pattern,’” he says. “It is not.”

For the rest of us who do need more than six hours of shut-eye a night, though, check out what happens in the body when sleep-deprived:

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