As they age, some people find it harder to stay asleep all night. A new study suggests that might be less of a modern affliction of aging and more a once-important benefit for the human family.
A study, published July 11 in Proceedings of the Royal Society of London B: Biology, suggests that the way sleep patterns change with age helped our ancestors survive by ensuring someone in a community was awake at all times.
Researchers analyzed the sleep patterns of a society of hunter-gatherers in Tanzania called the Hadza. Thirty-three members of the Hadza community wore small watchlike tracking devices for 20 days.
The Hadza sleeping environment resembles that of earlier humans, researchers said. They sleep outdoors or in grass huts in groups of 20 to 30 people without artificially regulating temperature or light.
Out of more than 220 total hours of sleep observation, researchers found only 18 minutes when all adults were sound asleep simultaneously. Typically, participants in their 50s and 60s went to bed earlier and woke up earlier than those in their 20s and 30s.
On average, more than a third of the group was alert, or lightly dozing, at any given time.
The researchers called this phenomenon the "poorly sleeping grandparent hypothesis," suggesting that an older member of a community who woke before dawn could have been crucial to spotting the threat of a hungry predator while younger people were asleep. It may explain why people slept in mixed-age groups through much of human history.
"We may be looking at just another reason why grandparents were critical in human evolution," said Alyssa Crittenden, an author of the study and an associate professor of anthropology at the University of Nevada, Las Vegas.
ActiveStyle on 08/21/2017