For most of human history, continuous eight-hour sleep has not been the standard. Instead, humans used to sleep in two distinct phases at night, often called a “first sleep” and “second sleep,” separated by a period of wakefulness lasting an hour or more. Historical records from Europe, Africa, and Asia describe families going to bed early after nightfall, waking around midnight for quiet activities, and then returning to sleep until dawn.
This biphasic sleep pattern shaped how people experienced time during the long night, turning the hours into manageable segments. The intervals were not idle time but moments of productivity or reflection — people tended fires, prayed, contemplated dreams, read, wrote, or even socialized softly. Many couples took advantage of this night waking period for intimacy.
References to the two-sleep system can be found in ancient literature, such as the works of Homer and Virgil, indicating its prevalence. However, the practice began disappearing over the last two centuries, primarily due to societal changes driven by the Industrial Revolution and the widespread adoption of artificial lighting. Gradually, people stayed up later under lamplight and electric light, shifting the sleep schedule to a single consolidated block.
Extreme environmental conditions like polar winters and long cave confinements studied in sleep laboratories reveal how natural light cues influence sleep duration and perception of time. In conditions lacking clear light transitions, people’s circadian rhythms and time perceptions can become distorted.
Modern clinical observations recognize sporadic nighttime awakenings as normal. Cognitive behavioral therapy for insomnia advises calmly accepting intermittent wakefulness, avoiding clock-watching, and engaging in quiet, low-light activities to ease back into sleep.
This deep history and understanding of human sleep patterns provide a fresh perspective on insomnia and modern sleep challenges, suggesting our continuous sleep habit is a relatively recent cultural adaptation rather than an evolutionary constant.
