On dry nights, the San hunter-gatherers of Namibia often sleep under the stars. They have no electric lights or new Netflix releases keeping them awake. Yet when they rise in the morning, they haven’t gotten any more hours of sleep than a typical Western city dweller who stayed up doomscrolling on their smartphone.

Finally, review the form thoroughly for any other questions or sections that need to be completed. Fill them out as required or leave them blank if not applicable. To tie together the story of how human sleep evolved, Samson laid out what he calls his social-sleep hypothesis in the 2021 Annual Review of Anthropology. He thinks the evolution of human sleep is a story about safety—specifically, safety in numbers. Brief, flexibly timed REM-dense sleep likely evolved because of the threat of predation when humans began sleeping on the ground, Samson says. And he thinks that another key to sleeping safely on land was snoozing in a group.

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It’s an amazing honor and opportunity to work with these communities,” says Samson, who has worked with the Hadza hunter-gatherers of Tanzania, as well as with various groups in Madagascar, Guatemala, and elsewhere. Study participants generally wear a device called an Actiwatch, which is similar to a Fitbit with an added light sensor, to record their sleep patterns. Our ancestors transitioned out of the trees to live on the ground, and at some point started sleeping there too. This meant giving up all the perks of arboreal sleep, including relative safety from predators such as lions. A lot of people in the global North and the West like to problematize their sleep,” he says. But maybe insomnia, for example, is really hypervigilance — an evolutionary superpower. “Likely that was really adaptive when our ancestors were sleeping in the savannah.”

Fossils of our ancestors don’t reveal how well-rested they were. So to learn about how ancient humans slept, anthropologists study the best proxy they have: contemporary non-industrial societies. And there’s reason to suspect we haven’t. In a 2008 study, Rattenborg and colleagues attached EEG devices to three wild sloths and found that the animals slept about 9.5 hours per day. An earlier study of captive sloths, on the other hand, had recorded nearly 16 daily hours of sleep. We’re not objective about our own sleep.Even if you feel like you sleep great, you can’t judge the quality of your own sleep because you’re unconscious while you’re sleeping. People with sleep apnea stop breathing several times per houreach night and wake up with zero recollection of everything they went through during the night. The amnesiac effect of sleep prevents usfrom knowinganything at all about what is going on in our bodies while we sleep. Not even your sleeping partner can answer this question — because they’re asleep too. Jen’s StoryWhen patients are referred to my office, it’s usually by their orthodontist. However, I also work with Ear, Nose, and Throat doctors (ENTs), pediatric dentists, general dentists, chiropractors, speech pathologists, allergists, and many other specialists. No matter who refers a patient or why, the first thing I screen for in every patient is an open mouth. Yetish says that studying sleep in small-scale societies has “completely” changed his own perspective.

Gandhi Yetish, a human evolutionary ecologist and anthropologist at UCLA, has also spent time with the Hadza, as well as the Tsimane in Bolivia and the San in Namibia. In a 2015 paper, he and other researchers assessed sleep across all three groups and found that it averaged between only 5.7 and 7.1 hours. And so Yetish suggests that ancient humans may have traded some hours of sleep for sharing information and culture around a dwindling fire. “You’ve suddenly made these darkness hours quite productive,” he says. Our ancestors may have compressed their sleep into a shorter period because they had more important things to do in the evenings than rest. Deep stage sleep is different from all the other stages of sleep and is key to reversing the aging process and preventing disease. How much we sleep is a different question, of course, from how much we wish we slept. Samson and others asked Hadza study participants how they felt about their own sleep. Out of 37 people, 35 said they slept “just enough,” the team reported in 2017. The average amount participants slept in that study was about 6.25 hours a night. But they awoke frequently, needing more than nine hours in bed to get those 6.25 hours of shut-eye.Humans, then, seem to have evolved to need less sleep than our primate relatives. Samson showed in a 2018 analysis that we did this by lopping off non-REM time. REM is the sleep phase most associated with vivid dreaming. That means we may spend a larger proportion of our night dreaming than primates do. We’re also flexible about when we get those hours of shut-eye.

Yetish describes a typical evening with the Tsimane: After spending the day working on various tasks, a group comes together around a fire while food is cooked. They share a meal, then linger by the fire in the dark. Children and mothers gradually move away to sleep, while others stay awake, talking and telling stories. Most people don’t realize that mouth breathing is a complex health concern. As a myofunctional therapist, I hear stories like this all the time. Yetish, who studies sleep in small-scale societies, has collaborated with Samson on research. “I do think that social sleep, as he describes it, is a solution to the problem of maintaining safety at night,” Yetish says. However, he adds, “I don’t think it’s the only solution.” Some forms may include spaces to indicate the actual time you went to bed and woke up. Enter the corresponding times in these sections. For example, if you went to bed at 10 PM and woke up at 6 AM, write these times accordingly. Humans, then, seem to have evolved to need less sleep than our primate relatives. Samson showed in a 2018 analysis that we did this by lopping off non-REM time. REM is the sleep phase most associated with vivid dreaming. That means, assuming other primates dream similarly, we may spend a larger proportion of our night dreaming than they do. We’re also flexible about when we get those hours of shut-eye.Now that you are aware of these symptoms, you can look for them in yourself or your child. You can get started by doing the following: Chances are, if you’ve done any reading on the importance of sleep, you know about the proverbial eight hours.