Enigmatic Biphasic Sleep Deciphered!

• In the Middle Ages, communal sleeping was entirely normal
• casual references to the system of twice-sleeping in every conceivable form
• To minimise any awkwardness, sleep involved a number of strict social conventions
• One major side-effect of much of humanity’s shift in sleeping habits has been a change in attitudes

For millennia, people slept in two shifts – once in the evening, and once in the morning, reports BBC.

The book 

Originally, Ekirch had been researching a book about the history of night-time, and at the time he had been looking through records that spanned the era between the early Middle Ages and the Industrial Revolution. He was dreading writing the chapter on sleep, thinking that it was not only a universal necessity – but a biological constant. 

Search for more references 

Over the coming months, Ekirch scoured the archives and found many more references to this mysterious phenomenon of double sleeping, or “biphasic sleep” as he later called it.

When Ekirch expanded his search to include online databases of other written records, it soon became clear the phenomenon was more widespread and normalised than he had ever imagined.

For a start, first sleeps are mentioned in one of the most famous works of medieval literature, Geoffrey Chaucer’s The Canterbury Tales (written between 1387 and 1400), which is presented as a storytelling contest between a group of pilgrims. 

They’re also included in the poet William Baldwin’s Beware the Cat (1561) – a satirical book considered by some to be the first ever novel, which centres around a man who learns to understand the language of a group of terrifying supernatural cats, one of whom, Mouse-slayer, is on trial for promiscuity.

But that’s just the tip of the iceberg. Ekirch found casual references to the system of twice-sleeping in every conceivable form, with hundreds in letters, diaries, medical textbooks, philosophical writings, newspaper articles and plays.

Ekirch began to suspect that the method had been the dominant way of sleeping for millennia – an ancient default that we inherited from our prehistoric ancestors. The first record Ekirch found was from the 8th Century BC, in the 12,109-line Greek epic The Odyssey, while the last hints of its existence dated to the early 20th Century, before it somehow slipped into oblivion.

How people slept in the 17th Century?

From as early as 21:00 to 23:00, those fortunate enough to afford them would begin flopping onto mattresses stuffed with straw or rags – alternatively it might have contained feathers, if they were wealthy – ready to sleep for a couple of hours. 

To minimise any awkwardness, sleep involved a number of strict social conventions, such as avoiding physical contact or too much fidgeting, and there were designated sleeping positions. 

A couple of hours later, people would begin rousing from this initial slumber. The night-time wakefulness usually lasted from around 11:00 to about 01:00, depending on what time they went to bed. 

The period of wakefulness that followed was known as “the watch” – and it was a surprisingly useful window in which to get things done. “[The records] describe how people did just about anything and everything after they awakened from their first sleep,” says Ekirch.

Once people had been awake for a couple of hours, they’d usually head back to bed. This next step was considered a “morning” sleep and might last until dawn, or later. Just as today, when people finally woke up for good depended on what time they went to bed.

An ancient adaptation

According to Ekirch, there are references to the system of sleeping twice peppered throughout the classical era, suggesting that it was already common then. It’s casually dropped into works by such illustrious figures as the Greek biographer Plutarch (from the First Century AD), the Greek traveller Pausanias (from the Second Century AD), the Roman historian Livy and the Roman poet Virgil.

Later, the practise was embraced by Christians, who immediately saw the watch’s potential as an opportunity for the recital of psalms and confessions. In the Sixth Century AD, Saint Benedict required that monks rise at midnight for these activities.     

But humans aren’t the only animals to discover the benefits of dividing up sleep – it’s widespread in the natural world, with many species resting in two or even several separate stretches. 

The sleep experiment 

Then back 1995, Ekirch was doing some online reading late one night when he found an article in the New York Times about a sleep experiment from a few years before.

The research was conducted by Thomas Wehr, a sleep scientist from the National Institute of Mental Health, and involved 15 men. After an initial week of observing their normal sleeping patterns, they were deprived of artificial illumination at night to shorten their hours of “daylight” – whether naturally or electrically generated – from the usual 16 hours to just 10. 

The rest of the time, they were confined to a bedroom with no lights or windows, and fully enveloped in its velvety blackness. They weren’t allowed to play music or exercise – and were nudged towards resting and sleeping instead.

At the start of the experiment, the men all had normal nocturnal habits – they slept in one continuous shift that lasted from the late evening until the morning. Then something incredible happened.

After four weeks of the 10-hour days, their sleeping patterns had been transformed – they no longer slept in one stretch, but in two halves roughly the same length. These were punctuated by a one-to-three-hour period in which they were awake. Measurements of the sleep hormone melatonin showed that their circadian rhythms had adjusted too, so their sleep was altered at a biological level.

Wehr had reinvented biphasic sleep. “It [reading about the experiment] was, apart from my wedding and the birth of my children, probably the most exciting moment in my life,” says Ekirch. When he emailed Wehr to explain the extraordinary match between his own historical research, and the scientific study, “I think I can tell you that he was every bit as exhilarated as I was,” he says.

As it turns out, biphasic sleep never vanished entirely – it lives on in pockets of the world today.

A new social pressure- industrial revolution 

Collectively, this research has also given Ekirch the explanation he had been craving for why much of humanity abandoned the two-sleep system, starting from the early 19th Century. As with other recent shifts in our behaviour, such as a move towards depending on clock-time, the answer was the Industrial Revolution.

“Artificial illumination became more prevalent, and more powerful – first there was gas [lighting], which was introduced for the first time ever in London,” says Ekirch, “and then, of course, electric lighting toward the end of the century. And in addition to altering people’s circadian rhythms. artificial illumination also naturally allowed people to stay up later.”

However, though people weren’t going to bed at 21:00 anymore, they still had to wake up at the same time in the morning – so their rest was truncated. Ekirch believes that this made their sleep deeper, because it was compressed.

As well as altering the population’s circadian rhythms, the artificial lighting lengthened the first sleep, and shortened the second. “And I was able to trace [this], almost decade by decade, over the course of the 19th Century,” says Ekirch.

Even if artificial lighting was not fully to blame, by the end of the 20th Century, the division between the two sleeps had completely disappeared – the Industrial Revolution hadn’t just changed our technology, but our biology, too.

A new anxiety

One major side-effect of much of humanity’s shift in sleeping habits has been a change in attitudes. For one thing, we quickly began shaming those who oversleep, and developed a preoccupation with the link between waking up early and being productive.

He explains that our sleeping patterns are now so altered, any wakefulness in the middle of the night can lead us to panic.

However, before Ekirch’s research spawns a spin off of the Paleo diet, and people start throwing away their lamps – or worse, artificially splitting their sleep in two with alarm clocks – he’s keen to stress that the abandonment of the two-sleep system does not mean the quality of our slumber today is worse.

A golden age for sleep 

Despite near-constant headlines about the prevalence of sleep problems, Ekirch has previously argued that, in some ways, the 21st Century is a golden age for sleep – a time when most of us no longer have to worry about being murdered in our beds, freezing to death, or flicking off lice, when we can slumber without pain, the threat of fire, or having strangers snuggled up next to us.

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Source: BBC

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