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In the early 1990s, psychiatrist Thomas Wehr conducted an experiment in which a group of people were plunged into darkness for 14 hours every day for a month. It took some time for their sleep to regulate but by the fourth week the subjects settled into a very distinct sleeping pattern. They slept first for four hours, then woke for one or two hours before falling into a second four-hour sleep. Though sleep scientists were impressed by the study, among the general public the idea that we must sleep for eight consecutive hours persists. More recently, the theory that humans slept in two distinct chunks has resurfaced, but in the rather less likely field of history.

Over the course of 20 years, historian Roger Ekirch at Virginia Tech undertook an intensive study into the human relationship with night for his book At Day's Close: Night in Times Past.

In diaries, court records, medical books and literature - from Homer's Odyssey to the anthropological account of modern tribes in Nigeria - he has found more than 500 references to a segmented sleeping pattern.

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Much like the experience of Wehr's subjects, these references describe a first sleep which began about two hours after dusk, followed by waking period of one or two hours and then a second sleep. "It's not just the number of references - it is the way they refer to it, as if it was common knowledge," Ekirch says. During this waking period people were quite active. They often got up, went to the toilet or smoked tobacco and some even visited neighbours. Most people stayed in bed, read, wrote and often prayed. Countless prayer manuals from the late 15th Century offered special prayers for the hours in between sleeps. And these hours weren't entirely solitary - people often chatted to bed-fellows or had sex. A doctor's manual from 16th Century France even advised couples that the best time to conceive was not at the end of a long day's labour but "after the first sleep", when "they have more enjoyment" and "do it better".

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Originally posted by Omega Vision
http://www.bbc.co.uk/news/magazine-16964783

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Originally posted by Symmetric Chaos
I completely fail to see how you can try to generalize the patterns of sleep that occur when people are exposed 14 hours of complete darkness to an actual day/night cycle. What was Wehr actually studying?

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Originally posted by Shakyamunison
How much do people sleep when there is no darkness?