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It is believed that in the modern world people are chronically sleep deprived. Sleep is disturbed by bright night lighting, glowing computer and TV screens, phone calls, coffee in unlimited quantities … At the same time, it is widely believed that our ancestors led a more natural and healthy lifestyle – in particular, they slept longer than us and often napped during the day.
Anthropologists from several American universities decided to test this assumption. To do this, they studied how people sleep in traditional hunter-gatherer tribes. The scientists observed in three traditional societies: the Hadza people in Tanzania, the Bushmen in Namibia, and the Chimane tribes in Bolivia. As a result, data were collected on the behavior of 94 people who were observed (in total) for 1165 days.
Sleep patterns were surprisingly similar across all three societies. “Despite differences in genetics and environment, in all observed groups, sleep was organized in almost the same way, which probably indicates that this sleep pattern is the most natural for Homo Sapiens as a biological species,” says one of the authors of the study. Jerome M. Siegel from the University of California at Los Angeles (USA).
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People in traditional societies observed by anthropologists slept between 5,7 and 7,1 hours per night (6,9 hours on average) – most people in developed countries sleep longer. They did not take a regular nap (it was previously believed that under “natural” conditions people tend to have a short daytime sleep), did not break their night sleep into two periods with an intermediate period of wakefulness (it is believed that such a sleep pattern was characteristic of the inhabitants of medieval Europe) and did not go to sleep after dark, despite the lack of modern means of lighting – they usually went to bed about three hours after sunset, and got up before dawn. Their organization of sleep was not so different from ours. It is noteworthy that most of the natives slept about an hour longer in winter. In developed countries, the average sleep time is usually almost independent of the seasons.
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Sleep in natural hunter-gatherer societies is mainly regulated by temperature and natural light levels. These mechanisms of sleep regulation in most cases do not work in modern society due to the abundance of sources of artificial light, heating and air conditioning.
An important difference between hunter-gatherers and residents of modern developed countries was that they are practically unfamiliar with insomnia (and, for example, in the United States, up to 20% of the population suffer from it). In the languages of the Chimane people and the Bushmen, there is no such word at all. The authors suggest that insomniacs in developed countries could benefit from a lifestyle somewhat similar to that of these tribes. First of all, this concerns limiting the impact of artificial lighting at night – it can disrupt the natural rhythms that regulate periods of sleep and wakefulness.
Подробнее см. G. Yetish et al. «Natural sleep and its seasonal variations in three pre-industrial societies», Current Biology, October 2015.