In today’s world where our homes are lit up in the evenings thanks to electricity, most of us would think we’d get less sleep than our ancestors. A new study says this is not true – it seems they probably used to sleep about 35 minutes less each night than we do today.
Team leader, Jerome Siegel, professor of psychiatry at UCLA’s Semel Institute of Neuroscience and Human Behavior, and colleagues from Yale University, UC Santa Barbara, and the University of New Mexico, followed the sleeping patterns of 98 individuals from traditional societies in South America and Africa.
According to the scientists, those societies had lifestyles closely resembling those of ancient hunter gatherers. It is the only study on the sleeping habits of people who maintain foraging and traditional hunting lifestyles in the present day.
Prof. Siegel with San people in the Kalahari Desert. (Image: UCLA)
Prof. Siegel said:
“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.”
The researchers wrote in the academic journal Current Biology (citation below) that the average American gets about 7 hours sleep each night, compared to the subjects they monitored for 1,165 nights, who only got 6 hours and 25 minutes.
The volunteers slept slightly longer in the winter compared to the summer.
Prof. Siegel said:
“The issue is: what is the data on how sleep has changed? And it occurred to me that these groups, which are rapidly disappearing, give the last opportunity to really know what human sleep was like before we all created our various civilizations. What is absolutely clear is that they don’t sleep more than we do.”
Bolivians, Tanzanians and Namibians monitored
The scientists fitted their volunteers – the Tsimane of Bolivia, San of Namibia, and Hadza of Tanzania – with wearable devices (wristwatches) that monitored how much they slept.
Prof. Sieger said:
“All three groups have pretty much the same sleep duration and pretty much the same timing of sleep. This gives me reasonable confidence that they reflect the common human biology and they are not a function of their particular situations, which are different.”
Sleep patterns of hunter gatherer communities in South America and Africa were monitored in this study. (Image: Cell Biology)
Not only did the volunteers sleep less at night, they hardly ever took naps.
Prof. Siegel said:
“There’s this myth that humans used to take daily naps, but that now — because we’re so busy and we can’t get back to our homes — we suppress the naps. In fact, napping, is relatively rare in these groups.”
Previously, anthropologists had suggested our ancestors, specifically hunter gatherers, used to get up during the night and sleep in ‘nocturnal shifts’. According to this latest study, this is not the case – they slept through the night.
Natural light not such a determining factor
People today talk about how artificial lighting, late night television, round-the-clock internet connection, and easy-to-use in bed smartphones rob us of our sleeping environment.
The researchers were surprised to find that natural light was not such an important factor in driving sleeping patterns. The majority of their volunteers fell asleep about 3.3 hours after the sun went down.
Temperature was found to have a much greater impact.
Prof. Siegel said:
“What we saw was quite striking – that sleep is occurring during this period of falling temperature and when the temperature hits bottom, they wake up. This is quite surprising.”
Lead author Gandhi Yetish, a Ph.D. candidate at the University of New Mexico, said:
“I feel a lot less insecure about my own sleep habits after having found the trends we see here.”
Their findings validate some current ideas about health and sleep, including the benefits of morning light, a cool bedroom temperature, and waking up at the same time each day.
Prof. Siegel, who is also chief of neurobiology research at the Veteran Affairs of Greater Los Angeles Health Care System, said:
“The fact that we all stay up hours after sunset is absolutely normal and does not appear to be a new development, although electric lights may have further extended this natural waking period.”
Less sleep and health
There was no evidence that their relatively short sleeping hours took a toll on their health. In fact, most studies have found that these groups have lower levels of blood pressure, atherosclerosis, and obesity, and higher levels of physical fitness than their American counterparts who sleep longer.
The researchers also found that insomnia is extremely rare among the people they monitored. In fact, there is no word for the sleeping disorder among the San and Tsimane communities.
Citation: “Natural Sleep and Its Seasonal Variations in Three Pre-industrial Societies,” Gandhi Yetish, Hillard Kaplan, Michael Gurven, Brian Wood, Herman Pontzer, Paul R. Manger, Charles Wilson, Ronald McGregor, Jerome M. Siegel. Current Biology. October 2015. 10.1016/j.cub.2015.09.046.