05. Sleep Myths and Realities: Lessons from hunter-gatherers

Jerry Siegel.
North Hills, USA


Sleep Myths and Realities: Lessons from hunter-gatherers


How did humans sleep before the modern era? Because the tools to measure sleep were developed long after the invention of the electric light, television, the Internet and related devices that are suspected of delaying and reducing sleep, there is no reliable data on how sleep has changed from levels more characteristic of our species’ evolutionary history.  To address this question, we have investigated sleep in three traditional human societies.  Despite their varying genetics, histories, and environments, we find that all three groups show similar sleep organization, suggesting that they express core human sleep patterns, probably characteristic of pre-modern era Homo sapiens.  Group sleep periods averaged between 6.9 and 8.5 h, amounts at the low end of durations reported for healthy subjects in industrial societies, with a difference of nearly one hour between summer and winter sleep durations.  Daily variation in sleep duration was strongly linked to the time of sleep onset, rather than the time of sleep offset. Although they lack electric lights, none of these groups began sleep near sunset, with sleep onset occurring, on average, 3.3 h after sunset.  Furthermore, awakening was usually before sunrise. The sleep period consistently occurred during the nighttime period of lowest environmental temperature, was not interrupted by extended periods of waking and terminated near the daily nadir of temperature.  Light exposure was maximal in the morning and greatly decreased at noon, indicating that all three groups seek shade at midday. Napping occurred on less than 7% of days in winter and 22% of days in summer.  Mimicking aspects of the natural environment experienced by these groups might be effective in treating certain modern sleep disorders.

My research is focused on the phylogeny of sleep and on brain mechanisms controlling sleep. This has included studies of the brainstem control of REM sleep and studies identifying the role of monoaminergic and reticular neurons in sleep and motor control.  In 2000 we, and others, reported that human narcolepsy was caused by a loss of hypocretin (orexin) cells in the hypothalamus, and we continue to investigate the function and role of this cell group. My current talk will be focused on sleep in human hunter-gatherers.

Recent publications can be viewed at: http://www.semel.ucla.edu/sleepresearch/

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