Human sleep differs in a lot of ways from the way our animal relatives rest. For one thing, it typically involves feathery pillows and not tree branches. But it’s also comparatively efficient, according to a new study in the journal Evolutionary Anthropology. Two researchers from Duke University examined the sleep patterns of hundreds of animals, including 21 primate species, to see how our sleep is different.
They found that we make do with a lot less sleep than some other species. Chimpanzees, for instance, sleep 11.5 hours a night, and gray mouse lemurs sleep up to 17. On the other hand, humans sleep for seven hours on average (and early hunter gatherer societies probably slept six to seven, as a different study found).
And humans make the most out of their sleep time. Much of that rest time involves rapid eye movement sleep (REM), the stage in the sleep cycle when people experience vivid dreams. REM makes up 25 percent of human sleep (and half of babies’ sleep, according to the National Institute of Neurological Disorders and Stroke), but for some primates like monkeys and lemurs, REM is only 5 percent of the total sleep cycle.
The researchers point out that many primates sleep in trees, rather than near the ground, as humans do. Great apes, for instance, make sleeping platforms in the trees, while smaller primates find holes or clusters of leaves to snooze in. They hypothesize that humans’ shorter, more intense pattern of sleep could be related to early hominins’ ability to sleep in groups near fires, protecting them from predators. Because they had this protection, they could spend more time in the useful but vulnerable stages of sleep like REM, while other animals might need to be in lighter sleep stages in order to be ready to defend themselves during the night.
But before you go touting how efficient your sleep is—and how you can function on just a few hours a night—remember that those seven plus hours are pretty important to your health, cognition, and more.