Our sleep is much more efficient than that of our closest animal relatives, a new study has found, allowing us to spend less time in the light stages of sleep, so we can drift more quickly into the deeper states that work so well at restoring our bodies and minds.
By evolving a more efficient method of sleep, we can get by on less - about 7 hours, on average - than other primate species. The southern pig-tailed macaque and the grey mouse lemur, for example, snooze for as many as 14 to 17 hours a day. What's more, some lemurs and monkeys enter the Rapid Eye Movement (REM) mode of sleep - which is of better quality than light dozing - for just 5 percent of the total time they're asleep, compared to around 25 percent for humans.
For the purposes of the study, the researchers from Duke University looked at data collected on hundreds of mammals across 21 different species of primates. The data was then analysed to look for slumber patterns in each species.
It turns out human beings are top of the tree in terms of both the brevity and the efficiency of sleep - we've somehow evolved to get better quality shut-eye in a shorter span of time. Chimpanzees, meanwhile - our closest animal relatives - sleep for an average of 11.5 hours a night.
Study co-author David Samson previously logged nearly 2,000 hours watching orangutans in REM and non-REM sleep as part of his dissertation research. He suggests that the shift in humans could have been caused by a switch from building beds in the trees to sleeping on the ground, and then to the comfortable beds we know today.
A more relaxed and warm sleep by the campfire may have originally helped us get more sustenance from a shorter period of slumber, they suggest.
The researchers also hypothesise that, as a species, we gradually cut down our sleeping hours to spend more time on more interesting pursuits: specifically, learning new skills and forging social bonds. Today, of course, it's Netflix binges and the glare of smartphones that are cutting down on our time in bed - but the research indicates the shift started happening a long time ago.
They also looked at a separate study of three remote hunter-gatherer societies in Tanzania, Namibia, and Bolivia, and found that they sleep for slightly longer than the rest of us. This suggests that it's not just the spread of electricity, technology, and an 'always-on' lifestyle that's behind our sleeping patterns, they say.
The researche has been published in Evolutionary Anthropology.