Did cavemen get more sleep than we do?
If you're feeling sleep deprived, you might not be able to blame it on modern society.
A study of hunter-gatherer societies suggests that our prehistoric ancestors slept for about the same number of hours we do today. And, contrary to the claims of siesta aficionados who say that we are biologically wired to sleep in the middle of the day, our ancestors likely didn鈥檛 nap.
In a in the journal Current Biology, scientists from American, Mexican, and South African universities describe how they monitored the sleep habits of people from three remote hunter-gatherer societies in Africa and Latin America that scientists believe most closely resemble our prehistoric ancestors.
鈥淭he question is, do we sleep less than these people,鈥� the study's author, Jerome M. Siegel, who at the University of California in Los Angeles, told 海角大神.
After studying a total of 94 adults from the Hadza tribe of northern Tanzania, the San in Namibia, and the Tsimane in Bolivia, Dr. Siegel and his team had their answer. 鈥淚t is absolutely clear that we don鈥檛,鈥� he said.
The researchers also observed that ambient light levels, contrary to popular belief, didn鈥檛 seem to influence when study subjects went to sleep or woke.
鈥淒arkness alone doesn鈥檛 force sleep and probably never has in humans,鈥� Siegel said.
This insight challenges widespread beliefs about our own sleep, or lack thereof. A host of maladies have been tied to our declining hours of sleep, and TV, the Internet, and city lights have been vilified for turning our civilization into a horde of insomniacs.
And it鈥檚 not just us: Anxiety around sleep predates computer screens by centuries, as sleep neuroscientist Jim Horne pointed out in the Telegraph.
Back in 1894, he writes, an editorial in the British Medical Journal claimed, 鈥淭he ." It goes on, "The hurry and excitement of modern life is held to be responsible for much of the insomnia of which we hear."
Siegel鈥檚 recent findings, the first to measure sleep habits among hunter-gatherers, he says, may help allay some of the persistent anxiety surrounding the "right" amount of sleep people need.
鈥淚鈥檓 not saying people shouldn鈥檛 worry about getting enough sleep,鈥� Siegel told the Monitor. What his research is showing, he says, is that 鈥渁mount of sleep is not related to health, necessarily, and that people should not be worried about short sleep that鈥檚 unaccompanied by other problems.鈥�
In their paper, Siegel鈥檚 team describes fitting adult men and women of the three tribes each with that constantly measured their wrist movements and the levels of light around them.
Over the course of three years, ending early this year, researchers found that their study participants 鈥� regardless of culture or environment 鈥� slept each night an average of 聽6.5 hours.
They didn鈥檛 take naps during the day, and most had no trouble falling or staying asleep. 鈥淚nsomnia鈥� is not even a word in their languages, says Siegel.
What鈥檚 more, researchers found that sunset didn鈥檛 induce sleep, and that sunrise didn鈥檛 necessarily wake people up. All the study participants 鈥� experiencing nearly identical lengths of night and day 鈥� went to sleep several hours after sunset.
Participants' sleep may have been unconnected to the amount of light, but the researchers found another correlation: temperature.
Regardless of the season, participants consistently awoke just as ambient temperatures reached their lowest point. 聽For the Tsimane and Hadza, who live on different continents, that was about an hour-and-a-half before sunrise. For the San in Namibia it was about an hour after the sun rose in the summer.
These findings suggests that temperature, not light, is a regulator of sleep. In modern society, Siegel says, our insulated buildings and artificial temperature-controlled environments could be throwing off our sleep rhythm.
鈥淲e don鈥檛 experience this substantial drop in temperature that our ancestors experienced,鈥� he explained. 鈥淧erhaps for some people and absence of this cue is making a difference.
This research raises other questions about sleep patterns. For one, if our tribal neighbors are sleeping the same number of hours but not complaining about insomnia or other health problems, are they getting better quality sleep?
鈥淥ne thing we don鈥檛 know is what kind of sleep they鈥檙e getting,鈥� said Siegel. 鈥淭hat鈥檚 the next thing I want to look at.鈥�
