Human evolution: among primtes we sleep less (Introduction)

by David Turell , Saturday, May 07, 2022, 00:44 (721 days ago) @ David Turell

Why the cause guesswork:

https://www.smithsonianmag.com/science-nature/why-humans-sleep-less-than-their-primate-...

"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. 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 around 9.5 hours out of every 24. Cotton-top tamarins sleep around 13. Three-striped night monkeys are technically nocturnal, though really, they’re hardly ever awake — they sleep for 17 hours a day.

"Samson calls this discrepancy the human sleep paradox. “How is this possible, that we’re sleeping the least out of any primate?” he says. 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 9.5 hours out of every 24, not seven. “Something weird is going on,” Samson says.

"Research by Samson and others in primates and non-industrial human populations has revealed the various ways that human sleep is unusual. 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. 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.

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"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. In a 2015 paper, he assessed sleep across all three groups and found that they averaged between only 5.7 and 7.1 hours.

"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.

"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 another key to sleeping safely on land was snoozing in a group.

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"A better understanding of how human sleep evolved could help people rest better, Samson says, or help them feel better about the rest they already get.

“'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.”

"Yetish says that studying sleep in small-scale societies has “completely” changed his own perspective.

“'There’s a lot of conscious effort and attention put on sleep in the West that is not the same in these environments,” he says. “People are not trying to sleep a certain amount. They just sleep.'”

Comment: I skipped through a lot of guesswork. No one knows why we sleep in shorter times. What is wrong with considering our very advanced different brain just works that way.?