Does Evolution Explain Why Our Sleep Habits Change With Age?

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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.

Human Body Temperatures Are Dropping, and Science Might Know Why

dcdp/iStock via Getty Images
dcdp/iStock via Getty Images

In 1868, German physician Carl Reinhold August Wunderlich started to popularize what’s become the most recognizable number in all of medicine: 98.6°F or 37°C, which is thought to be the normal average human body temperature. Though his methods later came under scrutiny—Wunderlich stuck an enormous thermometer under the armpits of patients for 20 minutes, a less-than-accurate technique—this baseline has helped physicians identify fevers as well as abnormally low body temperatures, along with corresponding illnesses or diseases.

More than 150 years later, 98.6° may no longer be the standard. Humans seem to be getting cooler. Researchers at Stanford University School of Medicine, in a paper published in the journal eLife, compared three large datasets from different time periods: American Civil War records, a national health survey from the 1970s, and a Stanford database from 2007-2017. By comparing recorded body temperatures, the researchers founds that men are now averaging a temperature .58°C less than what's long been considered normal, while women are .32°C lower. On average, each has decreased roughly .03°C every decade since the 1860s.

What drove us to chill out? Scientists have a few theories. A number of advances in human comfort have been ushered in since the 1800s, including better hygiene and readily available food, which may have slowed our metabolic rate (temperature is an indication of that rate). Chronic inflammation, which also raises body temperature, has decreased with the advent of vaccines, antibiotics, and better healthcare. The researchers propose that, on average, our bodies are healthier and slightly less warm.

After all, the average life expectancy in Wunderlich’s era was just 38 years.

[h/t The Independent]

Last Wild Grove of Wollemi Pines, the Endangered ‘Dinosaur Trees,’ Saved From Australia's Wildfires

Marina Denisenko, iStock via Getty Images
Marina Denisenko, iStock via Getty Images

Almost three decades after they were rediscovered, the ancient "dinosaur trees" of Australia's Wollemi National Park were nearly wiped out for good. Wildlife officials in New South Wales feared that the last natural stand of Wollemi pines would be counted among the billions of plants and animals destroyed by Australia's recent wave of wildfires. But thanks to quick action from firefighters, the ancient grove has been saved, The Guardian reports.

The first Wollemi pines date as far back as 200 million years, and the trees reached peak numbers 65 million to 34 million years ago. Since then, populations have shrunk so drastically that the species was thought to be extinct until it was rediscovered 26 years ago. Fewer than 200 wild specimens exist today, and they're all concentrated in a protected sandstone grove in Wollemi National Park, about 125 miles northwest of Sydney, Australia.

The Wollemi pines' fragile status means that one bad forest fire could spell its end. With this in mind, the New South Wales National Parks and Wildlife Service and NSW Rural Fire Service prioritized their protection this bushfire season. Before the Gospers Mountain fire spread to the canyons where the trees grow, a team of firefighters was sent there by helicopter to install an irrigation system. This kept the trees hydrated and made them less vulnerable to flames. Helicopters also dumped fire retardant around the grove to weaken the fire when it arrived.

The efforts weren't able be able to save every Wollemi pine from damage and destruction—a few trees survived with charring and two more died—but they were enough ensure the continuation of the species. With a population this small, protecting it is a never-ending battle. In addition to fire, visitors stepping on seedlings and introducing diseases also pose a threat. For that reason, the Australian government has chosen to hide the exact location of the grove from the public.

[h/t The Guardian]

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