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.
“Any time you have a mixed-age group population, some go to bed early, some later,” Nunn said. “If you’re older you’re more of a morning lark. If you’re younger you’re more of a night owl.”
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,” 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,” said Nunn, who also directs Triangle Center for Evolutionary Medicine, or TriCEM.Paper. (paywall) – David R. Samson, Alyssa N. Crittenden, Ibrahim A. Mabulla, Audax Z. P. Mabulla, Charles L. Nunn. Chronotype variation drives night-time sentinel-like behaviour in hunter–gatherers. Proceedings of the Royal Society B: Biological Sciences, 2017; 284 (1858): 20170967 DOI: 10.1098/rspb.2017.0967 More.
So this is what evolutionary medicine amounts to. Wow.
First, what evidence do we have that very many people lived to be more than fifty years of age before the modern era? Modern humans who still follow a hunter-gatherer lifestyle (as described among the Hamza people) might in fact have access to vaccinations, antibiotics, emergency operations and high risk deliveries at remote hospitals. So in terms of longevity, they cannot be strictly compared with humans who lived before the dawn of these life lengtheners, in terms of what proportion of their group consists of seniors (people over sixty). If very few people lived that long, even if the claims made in the study were valid, the advantage would not be enjoyed by many groups. It is hard to see how it would become fixed in the genral human population.
Non-“evolutionary medicine” reasons that seniors (of whom there are many today) have trouble sleeping are suggested to be
– the aged body produces less melatonin
– needed medications may interfere with sleep
– lifestyle habits, including alcohol, caffeine, and nicotine can reduce sleep
No information is provided by telling a fanciful tale about the Old Stone Age.
Note: New Scientist story here:
Humans live longer than many other mammals. One theory is that there’s an evolutionary advantage to living beyond reproductive age because grandparents can help look after the children in a group – the grandmother hypothesis.
This study suggests there may be another advantage: “We’re calling it the ‘poorly sleeping grandparent’ hypothesis,” says Samson. “Having a mixed-age demographic increases the sentinel-like behaviour within a group.”
It would have been best to start by demonstrating that very many grandmothers existed into the over-60 age group where people begin to have trouble sleeping.
See also: The Grandmother Hypothesis, yet again
Menopause caused by guys staying home
The Science Fictions series at your fingertips: Human evolution