Most of us have been taught that a good night’s sleep means one long, uninterrupted stretch of seven to nine hours. Wake up in the middle of the night? That’s a problem. Feel drowsy after lunch? Fight through it. But what if that model of sleep isn’t actually how humans are wired to rest? A growing body of historical evidence and modern research suggests that sleeping in two separate periods, a pattern known as biphasic sleep, may be more natural.
What is biphasic sleep?
Biphasic sleep describes any sleep pattern in which a person sleeps in two distinct segments within a 24-hour period, rather than one continuous block. According to the Sleep Foundation, it is also sometimes called segmented or bimodal sleep. Those two sleep periods can be arranged in different ways: a longer nighttime sleep paired with a short afternoon nap, or nighttime sleep divided into two segments separated by an hour or so of wakefulness. Either way, the defining characteristic is that sleep is split rather than consolidated.
Biphasic sleep is not a fare-fetched idea or trend. In fact, The Sleep Foundation notes that many animals practice it, including birds, insects, and various mammals. And for much of human history, it was simply how people slept.
History of Sleep
Before the industrial era transformed daily life, sleeping in two phases appears to have been the dominant pattern across much of the Western world. According to historian A. Roger Ekirch of Virginia Tech, who has spent decades researching preindustrial sleep, references to a “first sleep” and a “second sleep” appear in thousands of historical sources spanning centuries.
The pattern was remarkably consistent. Most preindustrial households would retire around 9 or 10 p.m., sleep for roughly three to three and a half hours, and then wake around midnight. During that waking hour, people would do a wide range of things: pray, reflect on their dreams, tend to children, eat a small meal, or visit neighbors. Then they would drift back to sleep for a second phase, waking near dawn. As Ekirch’s research documents, the earliest literary references to this pattern stretch back to Homer’s Odyssey and Virgil’s Aeneid, suggesting biphasic sleep was recognized long before the word existed.
As noted in research published by National Geographic, Russell Foster, a professor of circadian neuroscience at the University of Oxford, has confirmed that historical records of biphasic sleep in humans date back hundreds of years. Evidence of biphasic sleeping has been found on virtually every continent, not just in northern latitudes where long winter nights might force the pattern, but also in cultures near the equator where season-driven light changes are minimal.
The shift away from biphasic sleep began gradually in the 19th century, driven by industrialization and the widespread adoption of artificial lighting. When people could stay active well past sunset, the rhythm of first and second sleep slowly gave way to a single consolidated block.
Comparing Sleeps
Understanding biphasic sleep is easier when you see how it fits alongside other sleep patterns.
- Monophasic sleep: the current Western standard where all sleep happens in one uninterrupted block, typically at night. This became the dominant model during the industrial era when artificial lighting gave people the ability to extend their waking hours well past sunset.
- Polyphasic sleep: involves three or more sleep periods per day. Newborns are natural polyphasic sleepers, cycling in and out of sleep around the clock. In adults, unintentional polyphasic sleep can sometimes be a sign of a disrupted circadian rhythm or a condition like irregular sleep wake rhythm disorder.
- Biphasic sleep: sits between these two approaches while still allowing for a substantial nighttime rest while incorporating a structured second sleep period that many people find natural and restorative.
There is no single biphasic sleep schedule; the pattern can take several forms. The Sleep Foundation outlines three common variations:
The Siesta Schedule is practiced widely in parts of southern Europe, Latin America, and beyond. In this model, nighttime sleep is shortened to roughly five or six hours, and the gap is filled with a 60- to 90-minute midday nap. The afternoon timing is key: napping too late in the day can interfere with the ability to fall asleep at night.
The Midday Nap Schedule follows a similar structure, but with a shorter daytime sleep. Instead of a long siesta, the person takes a brief 20-30 minute nap and sleeps for a longer stretch at night, typically six to seven hours. This is perhaps the easiest version for people with conventional work schedules to incorporate.
The First/Second Sleep Schedule is the original historical pattern. Under this model, nighttime sleep is divided into two segments separated by roughly an hour of wakefulness around midnight. This mirrors what preindustrial populations across the world appear to have done naturally for centuries.
Regardless of which version you choose, the guiding principle remains the same: total sleep across the 24-hour period should still reach at least seven hours, per recommendations from the American Academy of Sleep Medicine and the Sleep Research Society.
Either way, the Alaska Sleep Clinic has you covered in your pursuit of healthy sleep. Connect with our staff today for a free consultation.
