On Biphasic Sleep

Sleep. It’s a third of all human lifespans, and, yet, we know relatively little about it compared to, say, our workaday lives. Besides, the practice itself evolves as our societies change. We try to “make up sleep” on weekends (something that scientists say we can’t do) and complain that we need more sleep than we’re getting. However, this lack of sleep may be our own doing in the modern world.

About half-past twelve o’clock, when Mr. Winkle had been revelling some twenty minutes in the full luxury of his first sleep, he was suddenly awakened by a loud knocking at his chamber-door. Charles Dickens, The Posthumous Papers of the Pickwick Club, 1836

Most of the western world attempts to get 7 to 8 hours of sleep per night these days. Many people would argue that they could “get by” on 6 hours and still function well. Those numbers (6,7, and 8) are fairly recent targets in human history for sleep duration. Understand that our pre-Industrial Revolution forebears slept in a vastly different manner.

Don Quixote followed nature, and being satisfied with his first sleep, did not solicit more. As for Sancho, he never wanted a second, for the first lasted him from night to morning, indicating a sound body and a mind free from care; but his master, being unable to sleep himself awakened him, saying, “I am amazed, Sancho, at the torpor of thy soul; it seems as if thou wert made of marble or brass, insensible of emotion or sentiment!” Miguel de Cervantes Saavedra (1547–1616), Don Quixote de la Mancha

Before the invention of electric lights, or even before the creation of a factory/mechanized society in the late 1700s/early 1800s in many parts of the western world, people slept in a 4-2-4 pattern. That is, many slept for four hours or so (from 7 or 8 until 11 or 12), then, they rose for an hour or two where they would write letters, journals, visit friends, prayed, or even simply sit and read or perform housework, etc. After this interlude (1 or 2 in the morning), they would then sleep another four hours–give or take–until sun up, thus sleeping in two phases. This made sense in a northern climate where the residents saw an absent sun for up to 14 hours per day. One will find references to “second sleep” in several books, letters, diaries, and even court cases of the pre-industrial age.

“He knew this, even in the horror with which he started from his first sleep, and threw up the window to dispel it by the presence of some object, beyond the room, which had not been, as it were, the witness of his dream.” Charles Dickens, Barnaby Rudge, 1840

The factory/industrial work day seems to have stopped this practice.  These changes included street and house lights that could burn all night at low cost and–interestingly–the increase in coffee consumption as a late-evening social ritual. Also, as leisure time became available to the middle class, the evening became a time for people to go out. Sleep times suffered as a result. Arriving home around 10:00 pm, the average person attempted to achieve the same amount of sleep (8 hours) in less time.

I arise from dreams of thee
In the first sweet sleep of night,
When the winds are breathing low,
And the stars are shining bright…
Percy Bysshe Shelley (1792–1822), “The Indian Serenade’

Along with the attempts to get a solid block of 8 hours of sleep came the 3-meal day (not common before) and the concept of eating meat more than on holidays or special occasions. These things became de rigueur for the urban middle class by the middle 1800s. Given that some scientists have demonstrated that we need neither 3 meals nor meat daily and that breaking up our sleep into segments is actually better for us, one could argue that the Industrial Age changed society for the worse rather than for the better.

In recent years, Wehr, et al, conducted experiments that showed, when subjected to 14 hours of darkness, subjects settled into a rhythm of four hours of sleep followed by two hours of wakefulness and then followed by four more hours of sleep. The subjects in the test awoke from the second sleep more refreshed, more productive, and happier throughout the day than did those who tried to get eight hours of uninterrupted sleep.

It was only in the morning, after awaking and happily falling off into a second sleep, that he enjoyed the peace and repose of both body and soul, which usually characterized his rest. When he again opened his eyes after this delightful morning’s nap, a joyous ray, cast by the rising sun through the bed curtains, danced on the counterpane like a streak of gold, and gave a marvellous brilliancy to its variegated embroideries. Alexandre Dumas, The Watchmaker, 1859

Consider, then, that humans in the northern hemisphere slept in two phases for millennia until the past two hundred years. Paris first lit its streets in the mid-17th century, then Amsterdam, and London followed two decades later. Having lights on the streets invited people to sleep less. And, so, they did.

We do.

Carry on.