healthHealth and Medicine

Scientists Find The Bizarre Reason You Sleep Less As You Get Older

The Hadza people of Tanzania still live the hunter-gatherer lifestyle many think our ancient ancestors practiced. Gabor Kovacs Photography/Shutterstock

The ubiquity of smartphones and technology often gets the blame for the apparent lack of sleep we get nowadays. However, new research suggests that perhaps we should be holding our ancestors a little more accountable for those sleepless nights.

It is thought that the differences in when some people go to bed and others wake up 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.


The latest study, published in the Proceedings of the Royals Society B, suggests that this variation in sleeping patterns ensures that there is always at least one person awake when some are at their most vulnerable (such as when 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 rests.

While most experiments on human sleeping patterns are conducted in tightly controlled laboratory settings, the researchers from the University of Toronto took their kit out into the field and monitored the sleep patterns of the Hadza people of Tanzania, who still live the hunter-gatherer lifestyle that many think we first started living thousands of years ago. The team gave 33 members of one tribe sleep monitors and tracked their 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.

The team 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 co-author David Samson in a statement. “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.”

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.


healthHealth and Medicine
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  • evolution,

  • sleep,

  • humans,

  • predators,

  • Hadza,

  • ancient ancestors