Anthropologist Suggests Eight-Hour Uninterrupted Sleep is Not the Historical Norm

Anthropologist Alyssa Crittenden argues that the commonly held belief that a restorative night’s sleep consists of eight uninterrupted hours is a modern construct, not reflective of historical human sleep patterns. Crittenden, based at the University of Nevada, Las Vegas, has studied the Hadza people of Tanzania—hunter-gatherers whose daily practices offer insights into human rest.

In a recent interview with HuffPost España, Crittenden described the notion of eight continuous hours of sleep as “physiologically, a fantasy.” She emphasizes that while sleep is essential, it does not always need to occur in one extended block. Public health guidelines currently recommend at least seven hours of sleep for adults within a 24-hour period, but individual needs vary widely based on age and personal circumstances.

In a 2017 study involving 33 Hadza participants, Crittenden's research uncovered unique sleep patterns. Over 393 days, the Hadza averaged 6.25 hours of sleep per day with 68.9% efficiency, closely linked to natural environmental changes like light and temperature. The study found that naps were prevalent, occurring on approximately 54% of observed days, with an average duration of about 47.5 minutes. This pattern demonstrates a flexible approach to sleep rather than relying on a singular nighttime period.

Historical analysis further complicates the perception of sleep. Historian Roger Ekirch has noted references to segmented sleep phases—“first” and “second” sleep—interrupted by periods of nighttime activity. However, a 2023 critique suggests caution in assuming a uniform two-phase sleep pattern across history, indicating a diversity in sleep habits shaped by cultural and environmental conditions.

Crittenden's research highlights that the Hadza's sleep behavior reflects a natural adaptation to their surroundings, where naps are integrated into their daily routine rather than compensatory measures for sleep deprivation. In contrast, modern sleep guidelines generally emphasize total sleep duration within a consistent schedule. The CDC advises adults aged 18 to 60 to aim for at least seven hours, acknowledging varying sleep needs over a lifetime.

The situation in Colombia illustrates how social practices can dictate sleep timing. An OECD report indicated that Colombians wake up at an average of 6:31 a.m., influenced by cultural, religious, and work-related factors. Unlike the Hadza, the Colombian example does not imply a differing biological sleep requirement but rather showcases the impact of societal expectations on sleep patterns.

Overall, these findings present a nuanced picture of human sleep, recognizing several viable forms, including consolidated nighttime sleep, segmented patterns, and daytime napping. Crittenden argues that understanding this flexibility is crucial in alleviating the anxiety surrounding the expectation of a perfect eight-hour sleep cycle, emphasizing the interplay of biology with cultural and environmental influences.