A few years ago, chronobiologists at the University of Colorado Boulder ran a now-famous study in which they plucked gung-ho volunteers from their gadget-ridden lives and stuck them in the woods without any technology. Within two weeks, the volunteers’ sleep-and-wake cycles shifted, and they naturally adopted a healthier schedule dictated by daily sunlight patterns. The takeaway: If we set aside our beeping, blinking electronics and sleep like our device-less ancestors, we’ll all be better for it.
A new study, however, suggests that we’ve over-romanticized the way in which our forefathers slept before artificial light came into play. For the study, published in the journal Cell, a team of researchers at UCLA studied three groups of modern hunter-gatherer peoples — the Hadza, San and Tsimane — found respectively in Namibia, Tanzania and Bolivia. Their question: How does sleep differ between those of us in modern society and those who live in a similar fashion to our pre-industrial ancestors.
In the current western world, most of us keep monophasic sleep schedules, bedding down each night for a single, eight-ish-hour block. But, there are those that subscribe to polyphasic or biphasic sleep schedules, in which they choose to divvy up their sleep into smaller, strategically spaced out chunks. The reasoning? Sleep was the norm until the industrial age, when the introduction of artificial light sent us down the path to spooning our iphones in bed.
As reported in The Atlantic, the study was made up of 94 participants who wore activity-monitoring devices that automatically recorded sleep stats as well as exposure to ambient light. Among other metrics, researchers examined the sleep schedule to which the tribes adhered.
So, did the members of these pre-industrial, hunter-gatherer peoples sleep like our ancestors did? No and, according to the researchers, led by Jerome Siegel, our ancestors didn’t necessarily either.
All participants, regardless of their cultural affiliation, slept for a continuous stretch of 6.9 to 8.5 hours, logging between 5.7 and 7.1 hours of deep sleep — figures that are comparable (or a a bit lower) to those of us in the modern, western world.
Based on the findings, Siegel doesn’t quite accept the widely-accepted narrative that early societies slept in two or more segmented chunks. And even if it was customary during the period preceding the industrial revolution to divvy up one’s sleep, Siegel posits that monophasic sleep was still the norm prior to that.
“The two-sleep pattern was probably due to humans migrating so far from the equator that they had long dark periods,” Siegel told The Atlantic. “The long nights caused this pathological sleep pattern and the advent of electric lights and heating restored the primal one.”
It's fair to argue we have no way to certify that some little-studied group of pre-industrial people living in a modern-day world are truly like our ancestors. Anticipating this, Siegel pointed out that he specifically chose three geographically and culturally diverse groups. Their shared sleep patterns therefore suggest our modern habit of sleeping in one block “is the basic human wiring, and reflects how humans sleep in the natural environment.”
Siegel’s work also suggests more diversity in our ancestral sleep patterns than perhaps staunch polyphasic adherents would like to think.
In addition to their sleep patterns, the Hadza, San and Tsimane shared something else in common that’s just as noteworthy: They have no word for insomnia. While culture and disease often go hand-in-hand, especially when it comes to conditions with a behavioral component, Siegel’s work, The Atlantic story said, offered three clues to explain the word’s absence: All three groups wake up before the sun rises, absorb the most natural light around 9 a.m., and then head indoors to escape the day’s heat; people with seasonal affective disorder, studies have shown, respond best to bright light therapy when it’s administered in the morning; and, lastly, participants kept consistent schedules. 7am is always 7am.
To be blunt, Siegel’s work will greatly influence how we think about sleep. It not only challenges a popular belief that had become dominant in the field, but also makes it clear that we’ve exaggerated the narrative about how our ancestors slept.