> “It is worth mentioning that anthropological studies conducted in tribes active at night show that human sleep can be highly polyphasic in certain cultures. Although they have different cultures and ways of life, both the Temiars of Indonesia and the Ibans of Sarawak have similar polyphasic sleep-wake behaviors (Petre-Quadens, 1983). Their average nocturnal sleep episode duration ranges between 4 and 6 hr, and nighttime activities (fishing, cooking, watching over the fire, rituals) at any one time involve approximately 25% of the adult members. Daytime napping is very common in both tribes: at almost any time of day, about 10% of the adult members are asleep. Whatever the cause of these polyphasic sleep patterns,whether the expression of an inborn ultradian rest-activity tendency or other factors, such populations exhibit extremely flexible and fragmentary sleep-wake cycles. The minimal contact with modern civilization could be one of the reasons for the preservation of this possibly ancestral sleep pattern.”
There's http://scienceblogs.com/clock/2006/10/what_is_a_natural_slee...
And then, for all the European examples, see http://www.historycooperative.org/journals/ahr/106.2/ah00034... The author apparently has a book on the same topic which I really ought to read, but the preceding is the article mentioned on his profile-page:
> _At Day’s Close: Night in Times Past_ (W.W. Norton, 2005), a sweeping study of nocturnal culture before the Industrial Revolution, which garnered four prizes, including an award given by the history honor society Phi Alpha Theta for the “best subsequent book” in all fields of history. His article in 2001, “Sleep We Have Lost: Pre-Industrial Slumber in the British Isles,” in the American Historical Review, earned two awards, including the James L. Clifford Prize given by the American Society for Eighteenth-Century Studies.