Communal sleep is more common in less developed societies than in the technologically advanced West, although it is not clear that this is a cultural preference, conscious choice, or consequence of less space per person in the living quarters.
Discover magazine profiled anthropologist Carol Worthman who studies primitive cultures and sleep practices in them. She thinks that the customs of surviving hunter-gatherer societies shed light on how all humans slept at one time. She described sleep for these people as a "very fluid state" happening whenever the individual feels sleepy. Nighttime sleep is a social activity, in contrast to the isolated environments most modern people spend the night in.
If this idea is true, and the natural way of sleeping is not an uninterrupted block of 7-8 hours, then you have to wonder if the sleep industry (doctors, pharmaceutical companies, mattress sellers, etc.) is attempting to divert us from our natural patterns. Rather than attempting to shoe-horn sleep into an idealized pattern, individuals should find the regimen that works best for their biology and lifestyle demands.
You might think tribal sleep means everyone sleeps and wakes at the same time, but that isn't how it plays out in big groups. Depending on the situation, some individuals might be designated look outs or protectors, and even if that is not the case different people will have different daytime experiences, maladies, and sleep patterns. It is a wrong to think that all sleep patterns in the camp are synchronized. But it's also true that social sleeping individuals influence each other. If a game breaks out, people might choose to get up and participate, waiting to sleep until later.
Nevertheless, sleep can be a social activity, and this is more obvious in primitive living arrangements. The modern pattern of individuals sleeping along or with one (sometimes sexual) partner is rare, historically. Throughout the ages, people have slept with or near their children, parents, siblings, neighbors, and other community members. Infants usually slept with their mothers. In primitive cultures, infants do not sleep alone, according to at least one anthropologist who speculates separation of mother and infant may contribute to the risk of sudden infant death syndrome. When babies started sleeping in separate rooms from their parents, incidence of sudden infant death syndrome rose. When the infant is cradled with the mother, the mother may sleep shallower, but can respond to subtle changes that may indicate breathing problems. Nighttime feedings are also easier this way as the parents do not have to get out of bed.
Sleep is tied up with mysticism, superstition, the divine, and the supernatural. Forced sleep deprivation (and the hallucinations that can result) are sometimes employed in religious ceremonies.
The ancient Egyptians with their death obsession spent a lot of religious energy on sleep, too. The elaborate hairstyles worn by the upper class prompted creation of a headrest for sleeping time to protect the hair and when a teen got a headrest it may have been a symbol of the transition from youth to adulthood. The headrests may have kept bugs off the head, too, as well as allowed cooling in the hot climate. The Egyptians also thought sleep was a time when they could communicate with the dead.
Historians Craig Koslofsky and Roger Ekirch point to a decline in bi-phasic sleep starting in Europe in the 1600s. Modern life is about uniphasic sleep (or at least an assumption of it) and much distress over nighttime awakenings may be due to the false notion that healthy sleep should be uninterrupted. Indeed, Ekirch identified hundreds of literary references from before 1900 to a first and second sleep periods An hour or two between the sleep periods was commonly reported, time that could be spent socializing, in prayer, or even in work.
Is sleep maintenance insomnia not a defect, but a description of normal sleep patterns? We are not willing to go that far. In healthy bi-phasic sleep the person does not experience multiple awakenings during the night, and more importantly, does not have daytime sleepiness. So we still say there is sleep maintenance insomnia even if we acknowledge that the ideal of a single block of uniphasic or monophasic sleep is probably a false ideal.
Electrification and the advent of lighting and electronic devices has been implicated in modern society's sleep problems. But the problem with this artificial light might not be that it mimics the Sun and screws with circadian rhythms as much as it encourages people to work and play over a greater period of the day - starting early and going late - and pushes time for sleep to a smaller window. The person may allow enough time for sleep, but attempt to get it all in one unbroken 8-hour period. Allowing 9 hours with time for nighttime awakenings may be more feasible.
Science abstract: Prolonged Sleep under Stone Age Conditions