Science · Mar 22, 2018
The History of Sleep and How it Has Changed Over History
The way we sleep seems natural. Depending on your age and your region, you may sleep anywhere from seven to ten hours per night, all in a single sitting.
For most of us, we have been sleeping this way since we were children and the habit has affected the way we perceive sleep. However, is it really the natural way our bodies nod off? The truth is so much more than just closing your eyes and giving in to your need to slumber. Our contemporary culture has shaped the way we recognize sleep; for a large part of human history, we didn't sleep the way we do now.
First Sleep and Second Sleep
If you go to bed at nine or ten in the evening, you may wake up anywhere from five to seven in the morning and start your day. Occasionally you'll find yourself waking up in the middle of the night to go to the bathroom or get a glass of water, but mostly, you will get through the night in one long session of sleep.
But over the last few decades, histories have been putting together pieces of how the past cultures have slept—it turns out, all of them slept differently from us. Instead of sleeping in one long stretch, people used to have two sleeping sessions—this was so common across cultures and regions around the world that this information was negligible, considering how ordinary it was.
Apparently, the average adult used to sleep around ten to twelve hours per day. The first sleeping session would begin at the start of the night, just after sunset and supper. This cycle would last anywhere from three to four hours, and then they would naturally wake up and stay awake for the next two hours. In these two hours, they would read, study, lie in bed, make love to their partner, or even visit the neighbors. Some would spend this time praying; religious manuals from the 14th and 15th centuries included certain prayers that were written for this two-hour period.
After two hours, people would find themselves sleepy once again and would sleep until morning, in a period that could last six to eight hours. Finally, those in warmer climates commonly slept a few hours in the afternoon to avoid the heat (a tradition which continues now in some countries).
So what was the purpose of this two hour period of wakefulness? A 15th century English doctor noted that the period between the first sleep and the second sleep was the ideal time for reflection and study; the brain was most awake and active after the first round of sleep. Another physician from 16th century France wrote that laborers found it easier to have children than those of higher birth because they more commonly made love to their wives after the first sleep, rather than before.
And as we know from modern culture, no one aside from the odd individual here and there practices this kind of sleeping routine. Which leads to the question: what happened to culture that changed the natural way that we sleep?
Electricity: The Development of Artificial Lighting
There are a few theories as to why we shifted from the two-sleep style of sleeping to the current one-sleep habit. All of these theories revolve around the invention of the lightbulb. The advent of streetlights and indoor electric lighting allowed people to continue with their days more easily even after the sun had gone. Whereas before electricity one was required to light a flame to read, write, or do any work around the house, the invention of the lightbulb enabled people to light up whenever they needed.
By the 1920s, our sleeping pattern had evolved entirely: instead of the two-sleep cycle with a gap in between, people slept later, spending their time socializing, working, and doing various activities longer into the night. Eventually, we stayed up later until there was no more time for two separate periods of rest.
Natural Sleeping: Physiological or Cultural?
In the 90s, top psychiatrist Thomas Wehr of the National Institutes of Mental Health held a study to understand the natural sleeping patterns of the human body. He had learned about the two-sleep pattern of pre-Industrial cultures, and decided to investigate on whether or not people would naturally fall back into a similar pattern or resort to the one they knew when taken off the clock of the modern world. Essentially, the study was an investigation on our exposure to light (photoperiodicity), and how this affects our sleeping patterns.
In Wehr's study, the psychiatrist took fifteen men and restricted their light intake in a controlled environment for four weeks. Instead of abiding by the usual sixteen hours of activity followed by eight hours of sleep, the participants stayed awake only ten hours per day, with the other fourteen hours spent in a dark room, where they would sleep or rest for the majority of the time. Wehr theorized that they were making up for their natural sleep debt, which is common amongst people who follow modern sleeping patterns.
After the first week of catching up on their sleep, they began to resort to two sleep sessions over a single night. In a twelve-hour period, they slept four to five hours for the first session, stay awake for a few hours, then sleep again until morning. Overall, they didn't sleep any longer than eight hours. Instead of tossing and turning and struggling to fall back asleep during this two-to-three-hour gap, they instead spent the time to relax, read, and not stress about their time or schedule.
Should We Sleep Like Our Ancestors Did?
While it's been proven that a two-sleep pattern is our natural tendency, science has yet to prove it is actually better. While you may feel more rested after two periods of sleep, this is only because you spent a longer period resting; though you only sleep for eight hours, another three to four hours were spent resting in that gap.
It would also be difficult to adjust to the two-sleep pattern in the modern world. With an average 9-5 job and the lights all around us—not to mention certain responsibilities to socialize and do other things at night—forcing your body to accommodate the two-sleep pattern may end up stressing you out more than it relaxes you.
But remember: sleep deprivation is a growing concern. Hundreds of millions of adults around the world sleep fewer than six hours per night, directly and indirectly leading to a rise in certain health conditions. It is crucial to prioritize securing a minimum of eight hours per night; whether you do this through the standard modern pattern or the two-sleep pattern of the past is up to you.
How much sleep do you really need? Read this blog post to learn about the best amount of Zzzs your body requires.
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