![]() He thinks the evolution of human sleep is a story about safety - specifically, safety in numbers. 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. We’re also flexible about when we get those hours of shut-eye. That means, assuming other primates dream similarly, we may spend a larger proportion of our night dreaming than they do. REM is the sleep phase most associated with vivid dreaming. Samson showed in a 2018 analysis that we did this by lopping off non-REM time. Humans, then, seem to have evolved to need less sleep than our primate relatives. In a 2015 paper, he assessed sleep across all three groups and found that they averaged between only 5.7 and 7.1 hours. Gandhi Yetish, a human evolutionary ecologist and anthropologist at the University of California, Los Angeles, has also spent time with the Hadza, as well as the Tsimane in Bolivia and the San in Namibia. 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. “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. So to learn about how ancient humans slept, anthropologists study the best proxy they have: contemporary non-industrial societies. ![]() This meant giving up all the perks of arboreal sleep, including relative safety from predators like lions.įossils of our ancestors don’t reveal how well-rested they were. Our ancestors transitioned out of the trees to live on the ground, and at some point started sleeping there too. (Apes such as gorillas sometimes also build beds on the ground.) They bend or break branches to create a bowl shape, which they may line with leafy twigs. Today’s chimpanzees and other great apes still sleep in temporary tree beds or platforms. ![]() Millions of years ago, our ancestors lived, and probably slept, in trees. Samson / American Journal of Physical Anthropology 2018 / Knowable Magazine From canopy bed to snail’s shell However, research on captive primates may not give an accurate picture of their sleep habits in the wild.Ĭ.L. In a 24-hour period, people spend the least time sleeping of any primate that’s been studied. The reasons for our strange sleep habits are still up for debate but can likely be found in the story of how we became human. We spend fewer hours asleep than our nearest relatives, and more of our night in the phase of sleep known as rapid eye movement, or REM. Research by Samson and others in primates and non-industrial human populations has revealed the various ways that human sleep is unusual. “Something weird is going on,” Samson says. A predictive model of primate sleep based on factors such as body mass, brain size and diet concluded that humans ought to sleep about 9.5 hours out of every 24, not seven. Sleep is known to be important for our memory, immune function and other aspects of health. “How is this possible, that we’re sleeping the least out of any primate?” he says. Samson calls this discrepancy the human sleep paradox. ![]() Three-striped night monkeys are technically nocturnal, though really, they’re hardly ever awake - they sleep for 17 hours a day. Chimps sleep around 9.5 hours out of every 24. Humans sleep less than any ape, monkey or lemur that scientists have studied. That’s a surprising number when you consider our closest animal relatives. Research has shown that people in non-industrial societies - the closest thing to the kind of setting our species evolved in - average less than seven hours a night, says evolutionary anthropologist David Samson at the University of Toronto Mississauga. 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 doom-scrolling on their smartphone. They have no electric lights or new Netflix releases keeping them awake. On dry nights, the San hunter-gatherers of Namibia often sleep under the stars. ![]()
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