The ubiquity of smartphones and technology often gets the blame for the apparent lack of sleep we seem to be getting nowadays. But new research suggests that perhaps we should really be holding our ancestors accountable for those sleepless nights, and not that latest spat on Twitter.
It is thought that the differences in when some people go to bed and others wake up, as well as restless nights experienced by many, could be a throwback to when our ancestors were sleeping in the bush, exposed to predators and other rival groups of humans as soon as the Sun went down.
This latest study, published in the Proceedings of the Royals Society B, suggests that this variation in sleeping patterns may be to make sure that there is always at least one person awake at any one time while some are at their most vulnerable (such as asleep). Known as the “sentinel hypothesis”, it is based on how other social animals, such as meerkats, always have someone on the lookout for predators while the rest of the group is resting.
While most experiments looking into human sleeping pattern conduct them on people in tightly controlled laboratory settings, the researchers from the University of Toronto took their kit out into the field and monitored sleep in the Hadza people of Tanzania, who still live in the hunter-gatherer lifestyle that many think we first started living thousands of years ago. Giving the 33 members of one tribe sleep monitors, the tracked the Hadza’s sleep patterns over 20 days and nights.
They found that during a period of over 200 hours, all members of the tribe were only asleep at the same time for an impressively short 18 minutes. The median was for eight individuals to be alert at any one time, accounting for 40 percent of all people living within the group.
But they also found a fascinating difference between the sleeping patterns of young Hadza and older Hadza people. It turned out that the younger people were more likely to be “night owls” while the grandparents were often “larks”.
“Researchers have theorized that one of the reasons grandparents live so long past their reproductive years is that their function is to take care of grandchildren,” explains coauthor David Samson, in a statement. “Our hypothesis is that their lark behaviour 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.”
So when the older members of your family shout at you for staying in bed late, just remind them that you’re doing it to protect them from lions in the middle of the night.