We might not experience life-or-death situations when our families go to sleep at night, but researchers think age-related insomnia is a holdover from our hunter-gatherer roots.
Researchers from Duke University in Durham, North Carolina, and the University of Nevada, Las Vegas, call their theory the “poorly sleeping grandparent hypothesis,” according to a news release.
Earlier in human history, mixed-age groups of people slept in close proximity and different sleep habits ensured that someone was always alert to be aware of any danger to the group.
The researchers studied the Hadza, a group of modern hunter-gatherers in Tanzania, who wore a small, watchlike device on their wrists for 20 days that tracked their nighttime movements.
They found that the Hadza sleep patterns varied. The majority went to bed around 10 p.m. and woke around 7 a.m. But some fell asleep as early as 8 p.m. and woke by 6 a.m., while the night owls stayed up past 11 p.m. and didn’t rise until after 8 a.m. In between, they woke several times during the night. Out of 220 hours, they found only 18 minutes when all adults were sound asleep.
“A lot of older people go to doctors complaining that they wake up early and can’t get back to sleep,” says Charlie Nunn, professor of evolutionary anthropology at Duke and co-author of the study. “But maybe there’s nothing wrong with them. Maybe some of the medical issues we have today could be a relic of an evolutionary past in which they were beneficial.”