A new study has found that humans can get by on significantly less sleep than other mammals because our sleep is more efficient.
Researchers from Duke University looked through the scientific literature and compiled a database of sleep patterns across hundreds of mammals, including 21 species of primates, including baboons, lemurs, orangutans, chimpanzees, and humans.
They found that humans are very short sleepers, getting by on an average of seven hours of sleep a night, while other primate species, such as southern pig-tailed macaques and gray mouse lemurs, need as much as 14 to 17 hours.
Our sleep also tends to be more efficient, according to the researchers.
We spend a smaller proportion of time in light stages of sleep, and more of our sleep time in deeper stages of sleep. For example, we spend 25 percent of our overall sleep in rapid eye movement sleep, or REM. But in primates such as mouse lemurs, mongoose lemurs, and African green monkeys, REM sleep barely climbs above five percent, the researchers noted.
“Humans are unique in having shorter, higher quality sleep,” said anthropologist and study co-author Dr. David Samson of Duke University, who logged nearly 2,000 hours watching orangutans in sleep as part of his dissertation research before coming to Duke.
The human sleep gap isn’t the result of around-the-clock access to artificial light and computer screens, the researchers add.
A separate study of the sleep habits of people living in three hunter-gatherer societies without electricity in Tanzania, Namibia, and Bolivia found they get slightly less sleep than those of us in modern societies rife with electronic gadgets.
If artificial light and other aspects of modern life were solely responsible for shortening our sleep, we’d expect hunter-gatherer societies without access to electricity to sleep more, Samson said.
The study by Samson and Duke anthropologist Dr. Charlie Nunn instead suggests that humans replaced sleep quantity with sleep quality long before modern technology changed our lives.
The researchers attribute the shift towards shorter, more efficient sleep in part to the transition from sleeping in trees, as our early human ancestors probably did, to sleeping on the ground.
Once on the ground, humans started sleeping near fire and in larger groups to keep warm and ward off predators, such as leopards and hyenas, habits that enabled our ancestors to get the most out of their sleep in the shortest time possible, Samson said.
Shorter sleep also freed up time that could be devoted to other things, like learning new skills and forging social bonds, he said. Deeper sleep helped cement those skills, sharpen memory, and boost brainpower, he added.
The study was published in the journal Evolutionary Anthropology.