If you ever wish you could live in a simpler time when the pressures of modern life didn't make you feel sleep-deprived, scientists have two words for you: Dream on.
A new study of three preindustrial societies reveals that our early human ancestors probably got about the same amount of sleep as we do. Members of the Hazda, San and Tsimane societies slumber for an average of only 5.7 hours to 7.1 hours at night — and for the most part, they don't take naps.
"They do not sleep more than most individuals in industrial societies," the study authors wrote Thursday in the journal Current Biology.
The notion that humans would get more sleep in a world devoid of artificial light, Starbucks and the Internet is as widespread as it is persistent. The authors of the study — which was spearheaded by Jerome Siegel, director of UCLA's Center for Sleep Research — noted that "complaints about reduced sleep time in the 'modern world' were made at least as far back as the 1880s."
Direct observation of our ancestors' sleep habits would require a time machine. So Siegel and his colleagues opted for the next best thing, observing three groups of people who still live as if the industrial revolution never happened.
Two of these groups are in Africa. The Hazda people live just south of the equator in northern Tanzania, where their food supply depends on hunting and gathering. The San live further south, in Namibia, and are also hunter-gatherers. The third group, the Tsimane, are hunter-horticulturalists in the rainforests of Bolivia.
Despite their lack of modern medicine, these people often live well past the age of 60 and sometimes into their 80s. That's a clear sign that their sleep habits certainly aren't detrimental to their health.
To learn more about their sleep patterns, the researchers outfitted volunteers with small activity monitors that are worn on the wrist like a watch. Those monitors showed that for members of all three groups, a typical night's sleep was a little more than six hours.
None of the study volunteers headed for bed when night fell. Instead, they stayed up for 2.5 to 4.4 hours after sunset, often lighting small, dim fires after dusk. Members of all three groups typically woke up about an hour before sunrise. The one exception was that during the summer, the San volunteers woke up about an hour after the sun rose.
The Hazda people live so close to the equator that day length and temperatures hardly vary throughout the year. But the San and Tsimane do experience seasons, which appears to influence their sleep. The San volunteers slept 53 minutes longer in the winter than they did in the summer, on average, and the Tsimane averaged an additional 56 minutes of shut-eye.
In another seasonal difference, the researchers found that napping was rare year-round, though more likely during the summer than the winter.
The consistency of sleep patterns across all three cultures was "striking," the researchers wrote. The implication is that staying up a few hours past sunset, sleeping for an average of 6.4 hours and then waking before sunrise is "central to the physiology of humans," not a recent adaptation to the modern age.
"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," they wrote.