Why We No Longer Sleep in Two Shifts and How That Altered Our Conception of Time

Throughout most of human history, it wasn't common to sleep eight hours straight. Uninterrupted sleep is a contemporary behavior, not a natural consequence of our evolution. And that helps explain why many of us still wake up at 3 a.m. and wonder if something is wrong. It might be helpful to know that this is a very human experience. Throughout most of human history, it wasn't common to sleep eight hours straight. Instead, people typically slept in two shifts each night, often referred to as "first sleep" and "second sleep." Each of these periods lasted for several hours and was interrupted around midnight by a period of wakefulness that could last an hour or more. Historical records from Europe, Africa, Asia, and other areas indicate that families went to bed early and then woke up around midnight for a while before that.