At one time, people expected interrupted sleep, reports Men’s Health.

What changed? As with everything, it was technology. When artificial lighting became widely available, people began realizing that tasks they had previously been unable to do in the dark were suddenly doable. Consequently, they began shifting their bedtimes later and later. As they did that, the space between the two sleep shifts shrank. Soon enough, it was just easier to sleep in one long shift through the night.