Modern sleep pattern of an 8 hour chunk at night didn't materialize until around the industrial revolution when time management and efficiency became more of an issue. 8 hours at night is not what humans naturally took to. For most of human history we had split sleep - or biphasic sleep - commonly referred to as First Sleep and Second Sleep, with a break in between where we caught up on reading or had sex. You can read accounts of first sleep and second sleep all throughout history from classical Greece and Rome to about the 19th century.