Home » Health »

Live-in grandparents helped our ancestors sleep safely

 

A sound night’s sleep grows more elusive as people get older.

But what some call insomnia may actually be an age-old survival mechanism, researchers report.

A study of modern hunter-gatherers in Tanzania, eastern Africa, found that, for people who live in groups, differences in age-related sleep patterns ensure that at least one person is awake at all times.

Scroll down for video 

A study of modern hunter-gatherers in Tanzania finds that, for people who live in groups, differences in age-related sleep patterns ensure that at least one person is awake at all times. Pictured is a Hadza man sleeping on the ground in northern Tanzania, Africa

A study of modern hunter-gatherers in Tanzania finds that, for people who live in groups, differences in age-related sleep patterns ensure that at least one person is awake at all times. Pictured is a Hadza man sleeping on the ground in northern Tanzania, Africa

A study of modern hunter-gatherers in Tanzania finds that, for people who live in groups, differences in age-related sleep patterns ensure that at least one person is awake at all times. Pictured is a Hadza man sleeping on the ground in northern Tanzania, Africa

IS INSOMNIA A BYPRODUCT OF EVOLUTION? 

The researchers found that the misaligned sleep schedules were a byproduct of changing sleep patterns common with age.

Older participants in their 50s and 60s generally went to bed earlier, and woke up earlier than those in their 20s and 30s.

They call their theory the ‘poorly sleeping grandparent hypothesis.’

The basic idea is that, for much of human history, living and sleeping in mixed-age groups of people with different sleep habits helped our ancestors keep a watchful eye and make it through the night. 

The team hope the findings will shift our understanding of age-related sleep disorders.

The researchers suggest that mismatched sleep schedules and restless nights are an evolutionary leftover from millennia ago when a lion lurking in the shadows may have attacked you at 2 am.

‘The idea that there’s a benefit to living with grandparents has been around for a while, but this study extends that idea to vigilance during nighttime sleep,’ said study co-author Dr David Samson of the Duke University in Durham, South Carolina.

The Hadza people of northern Tanzania live by hunting and gathering their food, following the rhythms of day and night just as humans did for hundreds of thousands of years before people started growing crops and herding livestock.

The Hadza live and sleep in groups of 20 to 30 people.

During the day, men and women go their separate ways to forage for tubers, berries, honey and meat in the savanna woodlands around Tanzania’s Lake Eyasi.

Each night they reunite in the same place, where young and old both sleep outside next to a makeshift fireplace, or together in huts made of woven grass and branches.

‘They are as modern as you and me, but they do tell an important part of the human evolutionary story because they live a lifestyle that is the most similar to our hunting and gathering past,’ said co-author Dr Alyssa Crittenden, of the University of Nevada, Las Vegas.

‘They sleep on the ground, and have no synthetic lighting or controlled climate – traits that characterised the ancestral sleeping environment for early humans,’ Dr Crittenden said.

As part of the study, 33 healthy men and women aged 20 to 60 wore a small watch-like device on their wrists for 20 days that recorded their nighttime movements.

The researchers suggest that mismatched sleep schedules and restless nights are an evolutionary leftover from millennia ago when a lion lurking in the shadows may have attacked you at 2 am (stock image)

The researchers suggest that mismatched sleep schedules and restless nights are an evolutionary leftover from millennia ago when a lion lurking in the shadows may have attacked you at 2 am (stock image)

The researchers suggest that mismatched sleep schedules and restless nights are an evolutionary leftover from millennia ago when a lion lurking in the shadows may have attacked you at 2 am (stock image)

Hadza sleep patterns were rarely in sync, the researchers found.

On average, the participants went to bed shortly after 10 pm and woke up around 7 am.

But some tended to retire as early as 8 pm and wake up by 6 am, while others stayed up past 11 pm and snoozed until after 8 am.

In between, they roused from slumber several times during the night, tossing and turning or getting up to smoke, tend to a crying baby, or relieve themselves before nodding off again.

As a result, moments when everyone was out cold at once were rare.

Out of more than 220 total hours of observation, the researchers were surprised to find only 18 minutes when all adults were sound asleep simultaneously.

On average, more than a third of the group was alert, or dozing very lightly, at any given time. 

The findings may help explain why Hadza generally don’t post sentinels to keep watch throughout the night – they don’t need to, the researchers said.

Their natural variation in sleep patterns, coupled with light or restless sleep in older adults, is enough to ensure that at least one person is on guard at all times.

THE STUDY 

As part of the study, 33 healthy men and women aged 20 to 60 wore a small watch-like device on their wrists for 20 days that recorded their nighttime movements.

Hadza sleep patterns were rarely in sync, the researchers found.

On average, the participants went to bed shortly after 10 pm and woke up around 7 am.

But some tended to retire as early as 8 pm and wake up by 6 am, while others stayed up past 11 pm and snoozed until after 8 am.

In between, they roused from slumber several times during the night, tossing and turning or getting up to smoke, tend to a crying baby, or relieve themselves before nodding off again.

As a result, moments when everyone was out cold at once were rare.

Out of more than 220 total hours of observation, the researchers were surprised to find only 18 minutes when all adults were sound asleep simultaneously. 

‘If you’re in a lighter stage of sleep you’d be more attuned to any kind of threat in the environment,’ said co-author Professor Charlie Nunn, an evolutionary anthropologist at Duke University. 

The researchers found that the misaligned sleep schedules were a byproduct of changing sleep patterns common with age.

Older participants in their 50s and 60s generally went to bed earlier, and woke up earlier than those in their 20s and 30s.

They call their theory the ‘poorly sleeping grandparent hypothesis.’

The basic idea is that, for much of human history, living and sleeping in mixed-age groups of people with different sleep habits helped our ancestors keep a watchful eye and make it through the night. 

The researchers hope the findings will shift our understanding of age-related sleep disorders.

‘A lot of older people go to doctors complaining that they wake up early and can’t get back to sleep,’ Professor Nunn said.

‘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.’

 

Related Posts

  • No Related Posts