How do humans manage get a lot less shuteye than its closest animal kin? The secret may lie in evolution, which had made our sleep more efficient.

Duke University researchers, writing in the journal Evolutionary Anthropology, collected data on sleep patterns among mammals that include 21 primate species, from people to orangutans.

Through statistical tools, humans emerged as outstandingly short sleepers in the bunch, getting by on seven hours of sleep on average. In contrast, other primates including gray mouse lemurs and southern pig-tailed macaques require as much as 17 hours of sleep.

“Humans are unique in having shorter, higher quality sleep,” said study author and anthropologist David Samson, who spent almost 2,000 hours observing orangutans in their rapid eye movement (REM) and non-REM sleep.

Humans also have a marked efficiency in their sleep, allotting a small period of time in light stages and more in the deeper stages. REM sleep makes up almost a quarter of overall human sleep, compared to barely above 5 percent in some primate counterparts.

Samson and co-author Duke anthropologist Charlie Nunn suggested that humans traded sleep quantity for quality way before the advent of smartphones and modern technology, contrary to the human sleep gap being potentially attributed to 24/7 access to computers and artificial light.

In fact, separate research on the sleep habits of hunter-gatherer, non-electricity powered cultures in Bolivia, Namibia, and Tanzania indicated that they got slightly less sleep than wired societies.

So what could have made shorter, more efficient slumber in humans possible? The researchers thought it’s partly because of the shift of early ancestors from sleeping in “tree beds” to sleeping on the ground.

On the ground, ancient people probably began to sleep near fire and in bigger groups to stay warm and repel huge predators. These, said the authors, are habits that could have made human ancestors get the most quality out of their sleep with the most time efficiency.

Shorter sleep, too, allowed them the time and energy for other pursuits, such as social bonding and learning new skills. At the same time, deeper sleep cemented those skills and enhanced memory and brain power, Samson added.

While scientists are yet to arrive at a consensus when it comes to the optimum amount of sleep every night, a recent study showed that getting at least eight hours a night can improve memory, such as in one’s ability to recall new names and faces.

Photo: Timothy Krause | Flickr

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