T. M. Luhrmann in the NYTimes:
This obsession with eight hours of continuous sleep is largely a creation of the electrified age. Back when night fell for, on average, half of each 24 hours, people slept in phases. In “At Day’s Close,” a remarkable history of night in the early modern West, Roger Ekirch writes that people fell asleep not long after dark for the “first sleep.” Then they awoke, somnolent but not asleep, often around midnight, when for a few hours they talked, read, prayed, had sex, brewed beer or burgled. Then they went back to sleep for a shorter period. Mr. Ekirch concludes, “There is every reason to believe that segmented sleep, such as many wild animals exhibit, had long been the natural pattern of our slumber before the modern age, with a provenance as old as humankind.”
A different regime, for example:
What have we lost with our dismissal of what the writer George Sturt called the “quiet depths of darkness”? In traditional non-Western societies like the Toraja, what happens at night really matters. People pay close attention to their dreams, and because they are awakened more often, they have more opportunity to remember them. When the anthropologist Eduardo Kohn arrived in a small village deep in the Amazon, people slept largely outdoors in an open thatch house, surrounded by other people. They would wake at night to drink tea, because it was cold, or because of the calls of animals. “Thanks to these continuous disruptions,” he writes, “dreams spill into wakefulness and wakefulness into dreams in a way that entangles them both.”