You may have heard your grandparents moaning about not being able to sleep.
No one has ever worked out why. Until now.
Researchers studied the hunter-gatherer community of Hazda people in northern Tanzania to see how people sleep in large groups.
The Hazdas sleep in groups of 20 to 30 people; either in grass huts or outside.
The study – which surveyed the sleep patterns of 33 healthy men and women between the ages of 20 to 60 – found that the reason for restless sleep with age is evolutionary.
Thousands of years ago, at least one member of a community would have to be awake at all times in order to ward off predators.
Results of the study found that this survival tactic may have stayed with us until this day, showing that sleep patterns were rarely in sync with over a third of the Hazdas either awake or lightly sleeping at any one time.
Out of more than 220 hours of observation, there were only 18 minutes when every single adult was asleep at the same time.
People in their 50s and 60s also went to sleep at a much earlier time compared to those in their 20s and 30s, suggesting further evidence of an evolutionary trait.
“A lot of older people go to doctors complaining that they wake up early and can’t get back to sleep,” commented author Charlie Nunn, professor of evolutionary anthropology at Duke University, North Carolina.
“But maybe there’s nothing wrong with them. Maybe some of the medical issues we have today could be explained not as disorders, but as a relic of an evolutionary past in which they were beneficial.”
“Any time you have a mixed-age group population, some go to bed early, some later. If you’re older you’re more of a morning lark. If you’re younger you’re more of a night owl,” he added.
“If you’re in a lighter stage of sleep, you’d be more attuned to any kind of threat in the environment.”