Have People Always Slept Through the Night?
Artificial light changed sleeping habits. People used to sleep in two phases, “first sleep” and “second sleep”, with two hours of time spent awake between. This practice of “segmented sleep” phased out between the late 17th century and early 20th century with the advent of new lighting technologies.
A video discussing sleep patterns before electricity.
How Artificial Light Changed the Sleeping Habits of Humans
To understand segmented sleep, we have to understand how artificial light has changed the way humans live. Below you will find a quick history of artificial light and how it has affected sleeping patterns:
- Artificial light is as old as humans creating the first fire. As early as 400,000 BCE we have evidence that suggest the use of fire by Prehistoric man.
- Bringing that light indoors via candles and lamps may have started as early as 500 BC when the Romans began using olive oil lamps.
- From about 220BC until about the 1800’s candles were commonly made from tallow (fat from cows or sheep). Tallow candles create an unpleasant smell when burned due to the glycerine they contain. Tallow candles were the most common and affordable type of candle (with the non-gross beeswax candles being a much more expensive alternative). People would typically make their own tallow candles, the process of which would create it’s own very unpleasant smell. Due to the costs and limitations of the tallow candle people tended to follow the natural light and dark cycle, despite their new lighting technology.
- Lighting and sleep patterns started to change more dramatically in the 18th century with the discovery spermaceti, an oil that comes from a cavity in the head of the sperm whale. It can burn longer than tallow and doesn’t have a foul smell.
- Around the same time people started using spermaceti a number of other new lighting technologies also took root. New lighting technologies included gas lighting that lit city streets and kerosene.
- By the early 20th century electricity could power not only cities, but electricity powered incandescent light bulbs could bring a proper light source in people’s homes for the first time. As electric light became more common, segmented sleeping patterns all but disappeared.
- Today artificial light from mobile phones, tablets, computers, and televisions continues to move sleeping patterns further away from the rhythms of the natural light / dark cycle.
What is Segmented Sleep?
Segmented sleep is two phases of sleep broken up by a two-hour period of being awake. It worked like this:
- First sleep accounts for the first 4 or so hours of sleep starting around the time the sun went down. This is like a nap to get your brain relaxed so you can enjoy the lost treasure of humanity “the period of wake-fullness” in between first and second sleep.
- The period of time awake in between the two sleeps usually started at midnight and lasted about two hours.
- Second sleep is simply the period after the period of being awake where one sleeps again until morning light (sometimes called morning sleep).
Why Did People Sleep in Two Phases?
In the simplest terms, people slept in two phases due to a lack of artificial lighting.
One could get very little done outside or inside the home at night without artificial lighting, therefore it was both common and natural to go to bed when the sun set and awake when the sun rose. The problem with this is that people would have had a very long sleep on long winter nights. So people naturally broke up sleep into two phases awaking in between to reflect on their day, pray, and do other things humans like to do at night such as drinking and fornicating.
The saying used to be something to the effect of “never conceive a child before first sleep”. Simply put, people got a nice rest in so they could enjoy their favorite nighttime activities with a fresh brain.
On an interesting side note, In Dreamland: Adventures in the Strange Science of Sleep, David K. Randall discusses how during the nocturnal waking period of a segmented sleep the hormone prolactin is released, along with other physiological changes. Prolactin is released with the relaxation that accompanies orgasm.
Why Did People Stop Sleeping in Two Phases?
It is likely that people stopped sleeping in two phases due to advent of new lighting technologies leading up to the industrial revolution. That is, we no longer had our lives dictated by the sun due to artificial light. This meant people could work later and get out of the house earlier, eliminating the need for an extra long “segmented sleep”.
Could This Be Wrong?
We have written history that tell us that people used to sleep in two phases, but there is always a chance we are simply misinterpreting “first sleep”, “beauty sleep”, and “early slumber” as two phases of sleep rather than just napping. Still there is considerable evidence that suggests our ancestors slept in two phases, including a study which showed humans would revert back to sleeping in phases if confined in a room that was dark for 14 hours out of the day (mirroring society before lighting techniques leading up to the industrial revolution).
The Consequences of Changing the Way we Sleep
In modern western society it is common to get less than the recommended amount of sleep. We used to follow the day night cycle, which can in some regions can mean a long time spent in segmented sleep. Today the average time slept is around 6 1/2 hours (according to some studies, see sleep debt), a far cry from 4 hours of sleep, 2 hours of relaxation, and then a whole other morning sleep. Studies have shown sleep debt to have health risks including decreased brain function.