From a very interesting Wall Street Journal piece on sleep, we learn some history about how humans used to get two sleeping chunks at night:
So why is sleep, which seems so simple, becoming so problematic? Much of the problem can be traced to the revolutionary device that’s probably hanging above your head right now: the light bulb. Before this electrically illuminated age, our ancestors slept in two distinct chunks each night. The so-called first sleep took place not long after the sun went down and lasted until a little after midnight. A person would then wake up for an hour or so before heading back to the so-called second sleep.
It was a fact of life that was once as common as breakfast—and one which might have remained forgotten had it not been for the research of a Virginia Tech history professor named A. Roger Ekirch, who spent nearly 20 years in the 1980s and ’90s investigating the history of the night. As Prof. Ekirch leafed through documents ranging from property records to primers on how to spot a ghost, he kept noticing strange references to sleep. In “The Canterbury Tales,” for instance, one of the characters in “The Squire’s Tale” wakes up in the early morning following her “first sleep” and then goes back to bed. A 15th-century medical book, meanwhile, advised readers to spend their “first sleep” on the right side and after that to lie on their left. A cleric in England wrote that the time between the first and second sleep was the best time for serious study.
The time between the two bouts of sleep was a natural and expected part of the night, and depending on your needs, was spent praying, reading, contemplating your dreams or having sex. The last one was perhaps the most popular. A noted 16th-century French physician named Laurent Joubert concluded that plowmen, artisans and others who worked with their hands were able to conceive more children because they waited until after their first sleep, when their energy was replenished, to make love.
The phrase is “segmented sleep” and it can be reproduced:
Studies show that this type of sleep is so ingrained in our nature that it will reappear if given a chance. Experimental subjects sequestered from artificial lights have tended to ease into this rhythm. What’s more, cultures without artificial light still sleep this way. In the 1960s, anthropologists studying the Tiv culture in central Nigeria found that group members not only practiced segmented sleep, but also used roughly the same terms to describe it.