Natural sleep and its seasonal variations in three pre-industrial societies.

TitleNatural sleep and its seasonal variations in three pre-industrial societies.
Publication TypeJournal Article
Year of Publication2015
AuthorsYetish G, Kaplan H, Gurven M, Wood B, Pontzer H, Manger PR, Wilson C, McGregor R, Siegel JM
JournalCurrent Biology
Date Published2015 Nov 2

How did humans sleep before the modern era? Because the tools to measure sleep under natural conditions were developed long after the invention of the electric devices suspected of delaying and reducing sleep, we investigated sleep in three preindustrial societies [1-3]. We find that all three show similar sleep organization, suggesting that they express core human sleep patterns, most likely characteristic of pre-modern era Homo sapiens. Sleep periods, the times from onset to offset, averaged 6.9-8.5 hr, with sleep durations of 5.7-7.1 hr, amounts near the low end of those industrial societies [4-7]. There was a difference of nearly 1 hr between summer and winter sleep. Daily variation in sleep duration was strongly linked to time of onset, rather than offset. None of these groups began sleep near sunset, onset occurring, on average, 3.3 hr after sunset. Awakening was usually before sunrise. The sleep period consistently occurred during the nighttime period of falling environmental temperature, was not interrupted by extended periods of waking, and terminated, with vasoconstriction, near the nadir of daily ambient temperature. The daily cycle of temperature change, largely eliminated from modern sleep environments, may be a potent natural regulator of sleep. Light exposure was maximal in the morning and greatly decreased at noon, indicating that all three groups seek shade at midday and that light activation of the suprachiasmatic nucleus is maximal in the morning. Napping occurred on <7% of days in winter and <22% of days in summer. Mimicking aspects of the natural environment might be effective in treating certain modern sleep disorders.

Alternate JournalCurr. Biol.
PubMed ID26480842
PubMed Central IDPMC4720388
Grant ListDA034748 / DA / NIDA NIH HHS / United States
I01 BX001753 / BX / BLRD VA / United States
MH064109 / MH / NIMH NIH HHS / United States
R01 DA034748 / DA / NIDA NIH HHS / United States
R01 MH064109 / MH / NIMH NIH HHS / United States
R01AG024119 / AG / NIA NIH HHS / United States