Are you a night owl or a morning lark? Do you tend to stay up late and sleep late in the mornings, or do you go to bed early and get up at the crack of dawn in a chipper mood? It turns out your nocturnal routine could have a more deep-rooted cause.
Previously, lousy sleep patterns were liked to our late-night smart phone use. A link was found between teen’s consumption of late night social media and depression and poor sleep. But, a new study shows that our agitated sleep can be an evolutionary relic, back to our hunter-gatherer days.
A recent study followed the chronotype variation in the Hadza, a group of modern-day hunter-gatherers in rural Tanzania. The research, published in Proceedings B, found that “sentinel theory” is applicable to humans.
The sentinel theory suggests that group-dwelling animals, like meerkats, developed mechanisms like (REM and dreams) to ensure that members of the group remained awake, to act as sentinels, while the rest of the group was asleep. This would keep the group protected from nocturnal threats.
David Samson, an assistant professor of anthropology at the University of Toronto spearheaded the research team. The team chose the Hadza for the study because they live very similarly to how our ancestors lived thousands of years ago. The tribe “lives in the same savannah grasslands that our ancestors had to overcome to adapt,” Samson said. “It’s the best current window into our evolution.”
The research team found that out of 13,000 total minutes, there were only 18 minutes were everyone in the entire group was asleep. They also found that at least 40 percent of the group was awake at any given time. They also found that chronotype was driven by age.
The researchers found that chronotype correlated with age. They found that the older people in the group tended to be morning larks, and get up early. They found that the younger Hadza of reproductive age tended to display night owl behavior.
Previous research has suggested that the natural function of grandparents is to help rear the children in the family. “Researchers have theorized that one of the reasons grandparents live so long past reproductive years is that their function is to take care of grandchildren,” Samson said. But, Samson believes that their research added an extra dimension to that hypothesis.
The research team believes that elderly people’s propensity to sleep less and wake up early has an evolutionary purpose. "Our hypothesis is that their lark behavior and shorter sleep times serve a function: the elders serve as sentinels at the times of day when others are sleeping. Therefore, it’s important to have people of all ages in any population," Samson said.
The study also found that western societies were getting more sound sleep compared to the Hadza. “What we’re finding in these populations is that total sleep time is fairly low. In western society, we’re actually getting more secure, decent sleep than hunter-gatherers,” Samson said.
Samson said that while tribes like the Hadza are actually getting less sleep, they are not as “paranoid” about sleep issues like people, especially the elderly, are in developed countries. Maybe that is just something that comes with age and we shouldn’t be as concerned about it.
Samson was amazed with the results of his study, and believes that there is no set normal sleeping pattern. “That figure blew me away,” Samson said. “It normalizes this propensity for variation and flexibility in human sleep.”
So maybe there is nothing wrong with your morning lark grandma or grandpa. This research shows that this is simply a behavioral trait that has carried over from our ancestors.
“While we tend to look at every deviation from the normal sleep pattern as a problem, It may just be part of human variation,” Samson said. “We are seeking to fill in a piece of the evolutionary puzzle.”