Consider the modern concept of “normal” sleep. Thanks to artificial illumination, I can stay active in the evening and delay my bedtime until about 11 p.m. I lock the door (to ensure security), turn down the thermostat (for optimal sleeping temperature), and turn off the lights (to eliminate extraneous stimulation). I join my wife (the cats and the rest of the family are elsewhere) in a room dedicated to sleeping (well, maybe a few other activities) where a soft mattress, covered with cotton sheets and a comforter, rests on a wooden platform. My expectation is that I will enjoy 7.5 hours (the U.S. adult average) of uninterrupted (one can always hope) sleep and awaken to the sound of an alarm clock.
This nightly routine of modern life seems so natural. Remarkably, it rarely applies to people living outside the Western world, or to our ancestors of 200 years ago. If you want an idea of how the human sleep cycle evolved, consider the sleep patterns of hunter-gatherers and traditional people, as described by the anthropologist Carol Worthman of Emory University.
Beds: Foragers like to keep it simple. The !Kung (northwest Botswana) sleep on a skin or sometimes just on the sandy ground. The Efe (Zaire) people sleep on thinly strewn leaves or perched between two logs. The Hiwi (Venezuela) use hammocks. None of these nomads use pillows or coverings. The more settled people such as the Gebusi (Paupau New Guinea) sleep on platforms made of wood strips and throw a barkcloth cape over their torso at night.
Bugs: Stinging and biting insects are a challenge to sleep and potentially cause disease. For settled people who live in shelters, an all-night smoky fire fumigates the thatch and keeps the mosquitoes at bay. The terrible air quality may actually have some health benefits. In one study the incidence of malaria was inversely correlated with nocturnal smoke levels.
Perhaps a reason that traditional people do without bedding is to avoid exposure to fleas and lice. The introduction of blankets in highland Papua New Guinea was associated with a dramatic increase in asthma among adults, probably due to infestations of house mites in the blankets.
Cultural beliefs, however superstitious, that reduce exposure to insects may also be health-promoting. For example, the fears of the Lese (Zaire) people that nightfall brings witches and spirit activity keeps them in their houses, with doors and windows tightly closed, thereby reducing the risk of mosquito bites and malaria.
Fires: People who live in the open often sleep around a robust fire that may be a matter of protection as much as heat and light. Modern people easily forget that large predators were once a major threat to humans, and continue to be so for some people. However, sleeping close to an open fire can be dangerous; virtually every member of one fire-tending group had scars from burns, sometime severe.
Bedmates: For most traditional people, solitary sleeping, or just with one’s spouse, is uncommon. Infants and small children virtually never sleep in a room alone. A typical configuration for the Efe is two adults, a baby, another child, a grandparent, a dog and perhaps a visitor, sleeping together in a 6 by 6 foot hut. One can only imagine the cries, sniffs, snores and movements as well as traffic from staggered bedtimes. The Gebusi women sleep with infants and children, packed like sardines, at the outer side of the longhouse. The men and boys in this highly male-superior society are segregated on an adjacent, roomier, sleeping platform.
Bedtimes: Among traditional people, the timing of sleep and wake is very fluid. For example, the !Kung stay up as long as there is something interesting going on—conversation, dance, music, story-telling. If a !Kung wakes up at night, he is likely to get up to play the thumb piano or join an almost perpetual conversation around the fire. No one is told to be quiet. There is no need for an assigned sentry — someone is always awake. For people living in the tropics, an afternoon nap during the heat of the day, is almost mandatory, and the nighttime sleep bout is concomitantly shortened. Modern sleep research has shown that the human circadian system is wired for daytime naps, with a biologically determined “post-lunch” dip, and peaks of alertness at dawn and dusk.
Rituals and altered states: For many traditional people, sleep is considered akin to a reversible death in which the soul temporarily leaves the body. A corollary of this belief is that the soul may wander too far and fail to return, resulting in an irreversible death. Frequent awakenings during the night are therefore reassuring and not to be avoided. Complete sleep deprivation is sometimes used to facilitate trance and altered states. For example, the Gebusi men hold all-night seances every 11th night, singing, chanting, and phasing in and out of sleep. Needless to say, visitations by the spirits are commonly reported.
Bringing anthropology into the laboratory
The observation that infants in traditional cultures never sleep alone led anthropologist James McKenna to speculate that sudden infant death syndrome (SIDS) could be related to the modern practice of relegating an infant to a crib in a separate room. He recorded the brain waves of mothers and infants who slept together and compared the patterns to mothers who slept apart. In both mothers and infants, co-sleep was lighter, more frequently interrupted but possibly safer for the infant.
Because the duration of the night in the natural environment exceeds the usual duration of human sleep, pre-modern people spent many hours awake but pinned-down by darkness. In a study conducted by Thomas Wehr at the National Institute of Mental Health (NIMH), volunteer subjects were confined to their completely darkened rooms for 14 hours per day (mimicking the duration of darkness in the winter). In adapting to total darkness, most subjects slept in two major bouts, separated by an interlude of drowsy wakefulness. During this time awake, the subjects often reported “meditating.” Wehr speculates that prehistoric people may have spent much of the night reflecting on their dreams, imparting an enhanced spiritual dimension to their lives.
What is normal sleep? It may not be “normal” to sleep in a single consolidated block of time, separated from the rest of the family, on a “heavily cushioned substrate” (as the anthropologists call a modern bed). Camping out reminds us of what sleep was like for our ancestors. Maybe it is more “normal” to sleep on the ground, together with one’s tribe, listening to the crackling sounds of a fire, without concern for bedtimes or alarm clocks, telling jokes and stories to pass the time, but perhaps a little worried about the bears who might be watching.
Robert Sack, M.D. is professor emeritus in the Department of Psychiatry at the Oregon Health and Science University. He is a specialist in sleep disorders.
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