#63 Human Sleep Paradox!
Saturday, May 07, 2022
Chimps sleep 9 hours a night. How is it possible that we are sleeping least out of any primates?
Research has shown that people in nonindustrial societies, the closest thing to the kind of setting our species evolved in, average less than seven hours a night. That’s a surprising number when you consider our closest animal relatives. Humans sleep less than any ape, monkey, or lemur that scientists have studied. Chimps sleep about nine and a half hours out of every 24. Cotton-top tamarins sleep about 13. Three-striped night monkeys are technically nocturnal, though, really, they’re hardly ever awake—they sleep for 17 hours a day, says David Samson, an evolutionary anthropologist at the University of Toronto, Mississauga.
Sleep is known to be important for our memory, immune function, and other aspects of health. A predictive model of primate sleep based on factors such as body mass, brain size, and diet concluded that humans ought to sleep about nine and a half hours out of every 24, not seven. Humans 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. 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.
Millions of years ago, our ancestors lived, and probably slept, in trees. Today’s chimpanzees and other great apes still sleep in temporary tree beds or platforms. 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 such as safety from predators such as lions. Brief, flexibly timed REM-dense sleep likely evolved because of the threat of predation when humans began sleeping on the ground.
It makes sense that the threat of predators may have led humans to sleep less than tree-living primates. In a 2008 study, Isabella Capellini and her colleagues found that mammals at greater risk of predation sleep less, on average. Although the evolution aspect of human sleep is interesting, we still are not sure if that’s the case because of the availability of data of other primates. It depends a lot on whether we have measured sleep in other primates accurately. Hence the paradox!
“Every time there is a claim that humans are special about something, once we start having more data, we realize they’re not that special”
~ Isabella Capellini
It is also possible that when our ancestors started living in communities, they traded a few hours of sleep fo sharing knowledge. 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. Our ancestors may have compressed their sleep into a shorter period because they had more important things to do in the evenings than rest.
Sometimes I wonder how will we describe our ‘sleep’ to an extraterrestrial specie if we ever encounter one? I mean obviously it isn’t necessary that they would require sleep to function properly, maybe it’s just something only limited to Earth and the way evolution happened here.
“Hey Alien! I need to lie unconscious for the next seven hours. During that time I will be thinking of some weird scenarios which might never happen in the real world, we call this process as dreaming. I might also snore but there’s nothing to worry about.”
See you next Saturday, until then have a great weekend :)
Cheers!
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