We often worry about lying awake in the middle of the night - but it could be good for you. A growing body of evidence from both science and history suggest that the eight-hour sleep may be unnatural.

In the early 1990s. psychiatrist 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 had settled into a very distinct sleeping pattern. They slept first for four hours, then woke for one or two hourss before "falling into a second four-hour sleep. Though sleep scientists were impressed by the study, among the general pub he the idea that we must sleep for eight consecutive hours persists.

In 2001, historian Roger Ekirch of Virginia Tech published a seminal paper, drawn from 16 years of research, revealing a wealth of historical evidence that humans used to sleep in two distinct chunks. Roger Ekirch says a 1595 engraving by Jan Saenredam is evidence of activity at night. His book "At Day's Close: Night in Times Past." published four years later unearths more than 500 reference to a segmented sleep pattern in diaries court records, medical boob and literature, from Homer's Odyssey to an anthropological account of modern tribes in Nigeria.

Ekirch found that references to the first and second sleep started to disappear during the late $$17^{th}$$ century. This started among the urban upper classes in northern Europe and over the course of the next 200 years filtered down to the rest of western society. By the 1920s the idea of a first and second sleep had receded entirely from our social consciousness. He attributes the initial shift to improvements in street lighting, domestic lighting and a surge in coffee houses - which were sometimes open all night. As the night became a place for legitimate activity and as that activity increased the length of time people could dedicate to rest dwindled.