Never heard this one before..............

Consider what life would have been like for a farmer in New England in 1700.  In the winter months the sun goes down at five, followed by fifteen hours of darkness before it gets light again.  And when that sun goes down, it's pitch black:  there are no streetlights, flashlights, light bulbs, fluorescents—even kerosene lamps haven't been invented yet.  There's just a flickering glow of a fireplace, and the smoky burn of the tallow candle.
     Those nights were so oppressive that scientists now believe our sleep patterns were radically different in the ages before ubiquitous night lighting.  In 2001, the historian Roger Ekirch published a remarkable study that drew upon hundreds of diaries and instructional manuals to convincingly argue that humans had historically divided their long nights into two distinct sleep periods.  When darkness fell, they would drift into "first sleep," waking after four hours to snack, relieve themselves, have sex, or chat by the fire, before heading back for another four hours of "second sleep."  The lighting of the nineteenth century disrupted this ancient rhythm, by opening up a whole array of modern activities that could be performed after sunset:  everything from theaters and restaurants to factory labor.  Ekrich documented the way the ideal of a single, eight-hour block of sleep was constructed by nineteenth century customs, an adaptation to a dramatic change int he lighting environment of human settlements.  Like all adaptations, its benefits carried inevitable costs: the middle-of-the-night insomnia that plagues millions of people around the world is not, technically speaking, a disorder, but rather the body's natural sleep rhythms asserting themselves over prescriptions of nineteenth century convention.  Those waking moments at three a. m. are a kind of jet lag caused by artificial light instead of air travel.

-Steven Johnson,  How We Got to Now:  Six Innovations That Made the Modern World