Roger Ekirch, professor of History at Virginia Tech found that we didn’t always sleep in one eight hour chunk. We used to sleep in two shorter periods, over a longer range of night. This range was about 12 hours long, and began with a sleep of three to four hours, wakefulness of two to three hours, then sleep again until morning.

What is surprising is not that people slept in two sessions, but that the concept was so incredibly common. Two-piece sleeping was the standard, accepted way to sleep.

This is actually backed up by science; in the 1990s, psychiatrist Thomas Wehr of the National Institutes of Mental Health conducted an experiment where fifteen men spent four weeks with their exposure to light restricted to mimic the light pattern of mid-winter of northern climes.

At first, the participants would do as you and I do today, and slept in a single, long period of time. Once they’d caught up on their own sleep debt, however, they switched to the exact same sleep pattern talked about in the historical journals noted above.

Generally, the men would sleep about four or five hours, then awake, then a few hours later go back to sleep.

So, this may be more natural, but is it actually better? It’s possible it is simply an evolved biological mechanic to deal with vastly different light and dark cycles depending on seasonal variation.

Via Slumber Wise for the full article.