Sleep evolution and history

Human sleep patterns have changed over the centuries, even if our need for sleep has not. At various periods throughout history people have gone to great lengths to make sleep more comfortable and safer, or to incorporate sleep into their lives to a greater or lesser extent. Many of our ideas about sleep vary from culture to culture as well as in response to the growth of scientific understanding.

Insomnia has been there for some time. An article published in the British Medical Journal in 1894 reads: ‘The subject of sleeplessness is once more under public discussion. The hurry and excitement of modern life is quite correctly held to be responsible for much of the insomnia of which we hear: and most of the articles and letters are full of good advice to live more quietly and of platitudes concerning the harmfulness of rush and worry.’

This timeline from Harvard Medical School interestingly traces the path of our sleep evolution and approach to and understanding of sleep throughout human history.

Sleep just recently

The current norm for staying awake all hours is very recent in historical terms. It really took root following the invention of the electric light bulb by Thomas Edison in 1879. Of course people did stay up after dark in the days before cheap electric lightning – just much less.

When humans depended on expensive candles or oil they went to bed earlier and stayed there longer, unless they were in the wealthy minority. Unlike our ancestors, we no longer have to sleep, doze or stay in bed just because it is dark. Cold weather was another good reason for staying longer in bed. But even in warm, sunny climates, our ancestors spent more of their time in bed, especially in civilisations that practised the siesta.

In modern industrialised societies we are exposed to an artificial day that is extended by electric lighting and typically lasts for at least 16 hours, regardless of the season. We now pack all of our sleep into a single block of time during the remaining seven or eight nights of darkness. This pattern of sleeping is biologically unusual: in most other species, sleep is split into two or more separate episodes in each 24-hour period. There are also reasons and mounting evidence for supposing that humans have not always slept in a single block either.

Historian Roger Ekirch of Virginia Tech published a seminal paper 2001 revealing a wealth of historical evidence that humans used to sleep in two distinct chunks.

Ekirch’s book At Day’s Close: Night in Times Past, published four years later, unearths more than 500 references to a segmented sleeping pattern – in diaries, court records, medical books and literature, from Homer’s Odyssey to an anthropological account of modern tribes in Nigeria.

segmented sleepSegmented sleep

Roger Ekirch argues that before the Industrial Revolution, segmented sleep was the dominant form of human slumber in Western civilization. He draws evidence using documents from the ancient, medieval, and modern world, which he discovered over the course of fifteen years of research. Other historians, such as Craig Koslofsky, have endorsed Ekirch’s discovery and analysis. According to Koslofsky, associations with ‘night’ before the 17th Century were not good. The night was a place populated by people of disrepute – criminals, prostitutes and drunks. Eventually cheap electricity changed everything – as did the norm of sleep.According to Ekirch’s argument, typically individuals slept in two distinct phases, bridged by an intervening period of wakefulness of up to an hour or more. A first sleep began about two hours after dusk, followed by waking period of one or two hours and then a second sleep.

During this waking period people were suprisingly active. They often got up, went to the toilet or smoked tobacco and some even visited neighbours. Most people stayed in bed, read, wrote and often prayed. Countless prayer manuals from the late 15th Century offered special prayers for the hours in between sleeps.

Peasant couples, who were often too tired after field labor to do much more than eat and go to sleep, awakened later to have sex. People also used this time to think and reflect, and to interpret dreams, which were more vivid at that hour than upon waking in the morning. This was also a favorite time for scholars and poets to write uninterrupted, whereas still others visited neighbors, or engaged in petty crime.

The human circadian rhythm regulates the sleep-wake cycle of wakefulness during the day and sleep at night. Ekirch suggests that it is due to the modern use of electric lighting that most modern humans do not practice segmented sleep, which is a concern for some scientists. Superimposed on this basic rhythm is a secondary one of light sleep in the early afternoon and quiet wakefulness in the early morning.

The modern assumption that consolidated sleep with no awakenings is the normal and correct way for human adults to sleep may lead many people to approach their doctors with complaints of maintenance insomnia or other sleep disorders. If Ekirch’s theory is correct, their concerns might best be addressed by assurance that their sleep conforms to historically natural sleep patterns.

By the 1920s the idea of a first and second sleep had receded entirely from our social consciousness. Night became fashionable and spending hours lying in bed was considered a waste of time. Sleep evolution was rewritten.

Sleep-sick society

Until recently in history people relied on the sun for their timekeeping. Moreover, they did not work in offices, factories or shops and they were not available 24/7 and required to be present at all times every day. Sleep has become increasingly devalued in the 24-hour sleep-sick society. Many of us regard sleep as wasted time and would prefer to sacrifice less of our busy lives. We live in a world where there are many sleep-deprived people and we pay a high price for neglecting sleep.

The scientific evidence tells us that far too many people in industrialized societies are chronically sleep-deprived with damaging consequences for their mental and physical health, performance at work, quality of life and personal relationships. William Dement, one of the pioneering scientists in the field, believes that we now live in a ‘sleep-sick society’.

Sleep and its disorders barely feature in the teaching of medicine, and few physicians are fully equipped to deal with the sleep problems. When researchers from Oxford University investigated British medical education in the late 1990′s, they discovered that the average amount of time devoted to sleep and sleep disorders in undergraduate teaching was five minutes, rising to 15 minutes in pre-clinical training. Your doctor is therefore unlikely to be an expert on the subject.

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