For many people, a good night’s sleep has become almost synonymous with eight uninterrupted hours: going to bed at the right time, staying asleep until morning and waking up feeling completely rested. Anthropologist Alyssa Crittenden argues that this ideal is more rigid than human sleep patterns have been throughout history.
Crittenden, an anthropologist at the University of Nevada, Las Vegas, has spent two decades making repeated field trips to Tanzania to work with the Hadza, a hunter-gatherer community whose daily routines offer researchers a different perspective on sleep and wakefulness.
In an interview with HuffPost España, Crittenden described the expectation of resting eight hours without interruption as “physiologically, a fantasy.” Her point is not that sleep is unimportant or that six hours is enough for everyone. Rather, her observations challenge the assumption that healthy human sleep must always occur in one continuous block.
For adults, current public health guidance recommends at least seven hours of sleep per 24-hour period. The amount needed varies by age and individual circumstances, and sleep quality matters alongside duration.
What do the Hadza reveal about sleep?
To examine real-world sleep patterns, a 2017 study led in part by Crittenden equipped 33 Hadza volunteers with activity monitors for a combined 393 days. The participants slept an average of 6.25 hours per day, with 68.9% sleep efficiency. Their sleep patterns were strongly aligned with natural changes in light, temperature and daily activity.
The researchers found another important feature: naps were common. A nap occurred on about 54% of observed days, and the average nap lasted about 47.5 minutes. The authors described the overall pattern as flexible, with a consistent early-morning sleep period and opportunistic daytime napping.
That pattern complicates the idea that nighttime sleep must carry the entire burden of daily rest. It also shows why the Hadza findings should not be reduced to the claim that humans “only need six hours.” The study examined one population living in a particular ecological and social environment; it did not establish a universal sleep requirement for adults.
Did people always sleep in one block?
Sleep has not always followed a single eight-hour block. Historian Roger Ekirch’s analysis of preindustrial sources, including court records, diaries and literature, identified references to a “first” and “second” sleep separated by a period of quiet nighttime activity.
That interpretation is not uncontested. A 2023 critique urged caution, arguing that historical sources point to diverse and flexible sleep habits rather than a uniform two-phase routine. Regardless of which pattern was more common, the historical record illustrates that human sleep schedules have adapted to cultural and environmental conditions.
What does the nap tell us about modern sleep?
The Hadza research is particularly interesting because napping appears as part of an ordinary sleep-wake pattern rather than simply as compensation for a poor night’s sleep.
In the 2017 study, the researchers linked Hadza sleep duration to environmental factors and described their sleep as strongly entrained to their surroundings. Their daytime naps were generally opportunistic, suggesting that sleep could be distributed across different parts of the 24-hour cycle rather than concentrated entirely at night.
Modern sleep advice, by contrast, usually focuses on getting enough total sleep while maintaining regular schedules. The CDC recommends at least seven hours for adults ages 18 to 60, while noting that sleep needs change with age.
That leaves room for an important distinction: eight hours is not the same thing as eight uninterrupted hours. A person can wake briefly during the night without necessarily having a sleep disorder, while persistent difficulty falling or staying asleep can require medical attention. The Hadza findings cannot be used to diagnose or dismiss sleep problems in other populations.
Colombia offers a different sleep pattern
Colombia provides a contemporary example of how social routines can shape the timing of sleep. An OECD dataset cited by EL PAÍS found that Colombians reported an average wake-up time of 6:31 a.m., earlier than the countries compared in the report. The newspaper attributed Colombia’s early schedules to several factors, including cultural and religious customs, work and school routines, and the country’s geographic location.
The Colombian example is different from the Hadza case: it does not show a different biological requirement for sleep. Instead, it illustrates how social expectations can influence when people get out of bed, regardless of how much sleep their bodies require.
Taken together, these examples point to a broader picture. Human sleep has appeared in different forms, including consolidated nighttime sleep, segmented nighttime sleep and sleep supplemented by daytime naps. The Hadza research adds evidence that sleep can remain flexible in response to environmental conditions.
For Crittenden, that flexibility is central to understanding why the modern expectation of a perfect, uninterrupted eight-hour night can create unnecessary anxiety. The scientific question is less about finding one universally “natural” sleep schedule than about understanding how biology interacts with environment, culture and individual needs.