Does Evolution Explain Why Our Sleep Habits Change With Age?

iStock
iStock

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.

Wayfair’s Fourth of July Clearance Sale Takes Up to 60 Percent Off Grills and Outdoor Furniture

Wayfair/Weber
Wayfair/Weber

This Fourth of July, Wayfair is making sure you can turn your backyard into an oasis while keeping your bank account intact with a clearance sale that features savings of up to 60 percent on essentials like chairs, hammocks, games, and grills. Take a look at some of the highlights below.

Outdoor Furniture

Brisbane bench from Wayfair
Brisbane/Wayfair

- Jericho 9-Foot Market Umbrella $92 (Save 15 percent)
- Woodstock Patio Chairs (Set of Two) $310 (Save 54 percent)
- Brisbane Wooden Storage Bench $243 (Save 62 percent)
- Kordell Nine-Piece Rattan Sectional Seating Group with Cushions $1800 (Save 27 percent)
- Nelsonville 12-Piece Multiple Chairs Seating Group $1860 (Save 56 percent)
- Collingswood Three-Piece Seating Group with Cushions $410 (Save 33 percent)

Grills and Accessories

Dyna-Glo electric smoker.
Dyna-Glo/Wayfair

- Spirit® II E-310 Gas Grill $479 (Save 17 percent)
- Portable Three-Burner Propane Gas Grill $104 (Save 20 percent)
- Digital Bluetooth Electric Smoker $224 (Save 25 percent)
- Cuisinart Grilling Tool Set $38 (Save 5 percent)

Outdoor games

American flag cornhole game.
GoSports

- American Flag Cornhole Board $57 (Save 19 percent)
- Giant Four in a Row Game $30 (Save 6 percent)
- Giant Jenga Game $119 (Save 30 percent)

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Map Shows How Everyone Blamed Syphilis on Everyone Else

Portrait of Gerard de Lairesse by Rembrandt van Rijn. De Lairesse, a painter and art theorist, had congenital syphilis that deformed his face and eventually blinded him.
Portrait of Gerard de Lairesse by Rembrandt van Rijn. De Lairesse, a painter and art theorist, had congenital syphilis that deformed his face and eventually blinded him.
Gerard de Lairesse, Wikimedia Commons // Public Domain

The origins of syphilis may be one of the greatest (and grossest) health mysteries of our time. Some historians claim that Christopher Columbus and his sailors contracted the sexually transmitted disease in the New World and brought it back to Europe. Other experts believe that the disease, which is caused by the bacterium Treponema pallidum, existed in various forms around the globe but was simply misclassified as other conditions. (European writers, including Italian historian Niccolo Squillaci, first described syphilis in the late 15th century.) And in 2015, researchers announced that they had identified signs of congenital syphilis in 14th-century skeletons from St. Polten, Austria, adding new evidence to an ages-old debate.

One thing's for sure: As the map below illustrates, nobody wanted to take credit for originating the virulent condition. Created by Redditor masiakasaurus (and spotted by The A.V. Club), the map illustrates the various nicknames Europeans gave the disease before the name syphilis caught on. (Italian physician and poet Hieronymus Fracastorius coined the word in 1530 with his poem "Syphilis Sive Morbus Gallicus" ("Syphilis or the French Disease"). Not surprisingly, nearly every single moniker used for the disease places blame on another group for giving birth to what by then had become a continental scourge.

“Most physicians felt that this was a new disease, that it hadn’t been seen before in Europe, and that view tended to prevail for quite some time,” medical historian John Parascandola told The Atlantic in 2016. “There were certain tempting reasons for people to accept that—blame it on the others, blame it on the outsiders. Before that, the French were blaming it on the Italians, the Italians were blaming it on the French, et cetera.”

Masiakasaurus sourced the syphilis nicknames from nine scholarly books/journals, including The Early History of Syphilis: A Reappraisal,The rise and fall of sexually transmitted diseases in Sweden, and A Medical History of Persia and the Eastern Caliphate: From the Earliest Times Until the Year A.D. 1932. You can view the full list on Reddit—after giving silent thanks to Alexander Fleming for discovering penicillin, found to be an effective cure for syphilis in 1943.

[h/t The A.V. Club]