Sleeping Troubles May Have Evolutionary Cause

New research reveals that sleeping difficulties in older patients may have their root in evolutionary selection pressures. Studying a tribe of modern hunter-gatherers in Tanzania, a group of researchers found that varying sleep patterns aid survival of the group.

Many people encounter trouble sleeping as they get older. Insomnia is a frequent problem facing the elderly, and many people report being unable to sleep until later and later into the night. These difficulties are often taken to be a sign that something is wrong. However, new research conducted by academics from UNLV, Duke University, and the University of Toronto, Mississauga suggests that trouble sleeping, especially among the elderly, may be a remnant of our evolutionary past. Having some members of a group awake during the night conferred significant survival advantages to our ancestors.

Sleep Study

The study, published in the anthropological journal Proceedings of the Royal Society B, studied the Hazda people, a group of modern hunter-gatherers from Tanzania. Research indicates that varying sleep cycles in its population, usually associated with age, allow at least some members of the community to remain awake and attentive to danger throughout the night. Similar studies have previously drawn such conclusions about animals like birds and mice, but this is the first study to identify this behavior in humans.

The Hazda are organized into small groups of 20 to 30 people, and they spend their days searching for food before reconvening to sleep near each other around a fire or in huts made of grass and branches. Essentially, they live today like our early ancestors did, making them a useful population to study. Learning about how they live can give us insight into earlier humans. The study involved 33 men and women between the ages of 20 and 60 who agreed to wear watch-like devices on their wrists for 20 days. These devices recorded their movements during the nighttime.

The Findings

Sleep patterns varied widely among the group, researchers found. The average sleep cycle began at 10 p.m. and ended at 7 a.m., but other versions of the cycle existed, some beginning hours earlier and others beginning hours later. All of them were roused at some point during the night, sometimes to relieve themselves and sometimes to perform activities like tending to infants or smoking.

Between the varying cycles and activity during the night, researchers found only 18 minutes out of all 220 hours of the study during which every member of the group was soundly asleep at the same time. Later bedtimes were correlated with older participants in the study, but none of the participants complained of sleep problems, suggesting that these were natural sleep routines for them.

The research suggests that many sleep ailments might not indicate a problem. They just might be a natural result of our evolutionary past.

As Charlie Nunn, professor of evolutionary anthropology at Duke puts it, “A lot of older people go to doctors complaining that they wake up early and can’t get back to sleep, but maybe there’s nothing wrong with them.” Their apparent problems, he continued, may be a “relic of an evolutionary past in which they were beneficial.”