A growing body of evidence from both science and history suggests that the eight-hour sleep may be unnatural. A psychiatrist conducted an experiment where a group of people were put in total darkness for 14 hours a day for a whole month. It took a while for them to regulate their pattern, but by the 4th week, they had settled for a very distinct sleeping pattern: they slept 4 hours, woke up for 2 and then slept for another 4.
Looking at historical data, it seems like that sleep pattern was not just widely accepted, it was also common knowledge. In fact, people used the time in between sleeps to talk or have sex. Doctors even recommended that time as the best time to conceive. It wasn't until the late 17th century that references to 1st and 2nd sleep started to disappear: it started in the upper classes and then it disappeared entirely by the 1920s.