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Does Evolution Explain Why Our Sleep Habits Change With Age?

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Laugh all you want now about Grandma's 8 p.m. bedtime; after reading this, you might just want to thank her. One team of researchers report that older adults' earlier body clocks may have evolved to ensure that at least one person was always awake to watch over a family group. They published their findings in the Proceedings of the Royal Society B.

Scientists believe that many groups of social animals take turns sleeping and standing guard. This sentinel hypothesis, as it's known, is easiest to observe in a line of sleeping ducks; the last duck in a row literally sleeps with one eye open. But we didn't know whether this phenomenon extended to humans.

To find out, researchers collaborated with Hadza people of northwestern Tanzania. Many Hadza maintain a hunter-gatherer lifestyle, working and sleeping far from the noise and light pollution of the cities. The researchers recruited a group of 33 adults between the ages of 20 and 60 and gave each person an actigraphic (movement-tracking) wristband. For 20 nights, the actigraphs recorded participants' tossing and turning, their waking, and their stillness in sleep.

The big-picture results looked a lot like you might expect. Average bed- and wake-up times were around 10 p.m. and 7 a.m., respectively. But those were just the averages. Within even this small group, two familiar chronotypes emerged: the older early birds, who bedded down around 8 p.m. and woke by 6 a.m., and the younger night owls, who were up past 11 p.m. and slept until 8 a.m.

Most compellingly, the researchers say, nobody ever slept through the night. Each person woke several times per sleep period, whether to pee, go for a smoke, soothe a crying baby, or just roll over in bed. The resulting gaps in sleep time meant that someone in the group was awake at almost all times. Out of 20 nights, there were only 18 minutes in which the entire group was sound asleep.

Co-author Charlie Nunn is an evolutionary anthropologist at Duke University. He says the group's early bird/night owl split, combined with the frequent mid-sleep awakenings, may be our bodies' way of keeping our families safe.

"If you're in a lighter stage of sleep, you'd be more attuned to any kind of threat in the environment," he said in a statement.

Nunn and his colleagues suggest that the staggered sleeping shifts are not an accident but an adaptation.

"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.”

Maybe. Maybe not. It's quite possible that older adults' sleep issues are just that: issues, and signs of an aging body. We'll need a lot more research on the subject before we can say for sure. In the meantime, let's cut Grandma some slack. Evolutionary advantage or no, we all just want to sleep.

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Medicine
Charles Dickens Museum Highlights the Author's Contributions to Science and Medicine

Charles Dickens is celebrated for his verbose prose and memorable opening lines, but lesser known are his contributions to science—particularly the field of medicine.

A new exhibition at London’s Charles Dickens Museum—titled "Charles Dickens: Man of Science"—is showcasing the English author’s scientific side. In several instances, the writer's detailed descriptions of medical conditions predated and sometimes even inspired the discovery of several diseases, The Guardian reports.

In his novel Dombey and Son, the character of Mrs. Skewton was paralyzed on her right side and unable to speak. Dickens was the first person to document this inexplicable condition, and a scientist later discovered that one side of the brain was largely responsible for speech production. "Fat boy" Joe, a character in The Pickwick Papers who snored loudly while sleeping, later lent his namesake to Pickwickian Syndrome, otherwise known as obesity hypoventilation syndrome.

A figurine of Fat Boy Joe
Courtesy of the Charles Dickens Museum

Dickens also wrote eloquently about the symptoms of tuberculosis and dyslexia, and some of his passages were used to teach diagnosis to students of medicine.

“Dickens is an unbelievably acute observer of human behaviors,” museum curator Frankie Kubicki told The Guardian. “He captures these behaviors so perfectly that his descriptions can be used to build relationships between symptoms and disease.”

Dickens was also chummy with some of the leading scientists of his day, including Michael Faraday, Charles Darwin, and chemist Jane Marcet, and the exhibition showcases some of the writer's correspondence with these notable figures. Beyond medicine, Dickens also contributed to the fields of chemistry, geology, and environmental science.

Less scientifically sound was the author’s affinity for mesmerism, a form of hypnotism introduced in the 1770s as a method of controlling “animal magnetism,” a magnetic fluid which proponents of the practice believed flowed through all people. Dickens studied the methods of mesmerism and was so convinced by his powers that he later wrote, “I have the perfect conviction that I could magnetize a frying-pan.” A playbill of Animal Magnetism, an 1857 production that Dickens starred in, is also part of the exhibit.

A play script from Animal Magnetism
Courtesy of the Charles Dickens Museum

Located at 48-49 Doughty Street in London, the exhibition will be on display until November 11, 2018.

[h/t The Guardian]

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Health
Feeling Down? Lifting Weights Can Lift Your Mood, Too
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There’s plenty of research that suggests that exercise can be an effective treatment for depression. In some cases of depression, in fact—particularly less-severe ones—scientists have found that exercise can be as effective as antidepressants, which don’t work for everyone and can come with some annoying side effects. Previous studies have largely concentrated on aerobic exercise, like running, but new research shows that weight lifting can be a useful depression treatment, too.

The study in JAMA Psychiatry, led by sports scientists at the University of Limerick in Ireland, examined the results of 33 previous clinical trials that analyzed a total of 1877 participants. It found that resistance training—lifting weights, using resistance bands, doing push ups, and any other exercises targeted at strengthening muscles rather than increasing heart rate—significantly reduced symptoms of depression.

This held true regardless of how healthy people were overall, how much of the exercises they were assigned to do, or how much stronger they got as a result. While the effect wasn’t as strong in blinded trials—where the assessors don’t know who is in the control group and who isn’t, as is the case in higher-quality studies—it was still notable. According to first author Brett Gordon, these trials showed a medium effect, while others showed a large effect, but both were statistically significant.

The studies in the paper all looked at the effects of these training regimes on people with mild to moderate depression, and the results might not translate to people with severe depression. Unfortunately, many of the studies analyzed didn’t include information on whether or not the patients were taking antidepressants, so the researchers weren’t able to determine what role medications might play in this. However, Gordon tells Mental Floss in an email that “the available evidence supports that [resistance training] may be an effective alternative and/or adjuvant therapy for depressive symptoms that could be prescribed on its own and/or in conjunction with other depression treatments,” like therapy or medication.

There haven’t been a lot of studies yet comparing whether aerobic exercise or resistance training might be better at alleviating depressive symptoms, and future research might tackle that question. Even if one does turn out to be better than the other, though, it seems that just getting to the gym can make a big difference.

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