Health
Humans’ Wounds Heal Much More Slowly Than Other Mammals’
Watching wild baboons in Kenya, Akiko Matsumoto-Oda, an evolutionary biologist and primatologist at the University of the Ryukyus in Japan, had a front-row seat to the violence between these monkeys, especially the males.
“I was struck by how frequently they sustained injuries,” she said, “and, even more, by how rapidly they recovered — even from seemingly severe wounds.”
Compared with her own experiences with nicks and cuts, the baboons’ ability to heal seemed like a superpower.
In a study published on Wednesday in Proceedings of the Royal Society B, Dr. Matsumoto-Oda and her colleagues compared the healing rates of humans, chimpanzees, monkeys and mice. They found that human wounds took more than twice as long to heal as wounds of any of the other mammals. Our slow healing may be a result of an evolutionary trade-off we made long ago, when we shed fur in favor of naked, sweaty skin that keeps us cool.
When possible, the researchers wanted to study healing in a way that was less violent and more controlled than watching wild baboons.
To measure human healing, they recruited 24 patients who were having skin tumors removed at the University of the Ryukyus Hospital. To gather data on chimpanzees, which are some of our closest animal relatives, researchers observed five captive chimps at the Kumamoto Sanctuary of the Kyoto University Wildlife Research Center, which houses animals formerly used in pharmaceutical research. The chimps’ wounds, like those of wild baboons, mostly came from tiffs between the animals.
The study’s other primate subjects, all kept at the Kenya Institute of Primate Research, included olive baboons, Sykes’ monkeys and vervet monkeys. Researchers anesthetized the monkeys, surgically wounded them and then monitored their recovery. “As a field researcher, I personally believe that invasive studies should be minimized as much as possible,” said Dr. Matsumoto-Oda, who noted that bite wounds on wild baboons are often similar in size to the surgical wounds in the study, but deeper.
Finally, to compare humans and primates with more distantly related mammals, researchers anesthetized and surgically wounded mice and rats.
Based on her field observations, Dr. Matsumoto-Oda was prepared to see humans healing more slowly than the other animals. The 24 people regrew skin at about a quarter of a millimeter per day, on average.
What surprised Dr. Matsumoto-Oda more was the consistency between the healing rates of the animal subjects, including chimpanzees. There was no significant difference in the speedy skin regrowth among different primates, which grew about 0.62 millimeters of new skin per day, or between primates and rodents. Humans were the clear outliers.
Elaine Fuchs, a stem cell biologist at the Rockefeller University who studies skin growth and repair and was not involved in the new research, said the results were what she would have expected. That’s because skin healing depends on hair.
Each hair grows from a hair follicle, which also houses stem cells. Normally, those stem cells just make more hair. But when called upon, they can grow new skin instead. “When the epidermis is wounded, as in most kinds of scratches and scrapes, it’s really the hair-follicle stem cells that do the repair,” Dr. Fuchs said.
Furry animals are covered in follicles, which help quickly close up wounds in mice or monkeys. By comparison, “human skin has very puny hair follicles,” Dr. Fuchs said. And our ancestors lost many of those follicles, packing their skin with sweat glands instead. Sweat glands also have stem cells, but they’re much less efficient at repairing wounds, Dr. Fuchs said.
Why did we make that trade during evolution, giving up so much of our hair and its protective properties? The glands that make the watery, salty sweat that dampens our shirts on a hot day are called eccrine glands. Most furry mammals have them only in certain places, mainly the soles of their paws. But human ancestors went all-in on sweat — modern humans have millions of sweat glands all over our bodies, and they’re about 10 times denser than those of chimpanzees.
“We evolved to cool by sweating profusely,” said Daniel Lieberman, an evolutionary biologist at Harvard University. Our abundant sweat glands and lack of fur let our ancestors engage in physical activity in hot environments, Dr. Lieberman said, and cooled the machinery of our big brains.
The benefits of trading hair for sweat must have outweighed the costs. Dr. Matsumoto-Oda and her co-authors speculate that social support among prehistoric humans might have helped wounded people stay alive, despite our slower healing. (Or maybe they had ways to treat wounds, like orangutans and chimps seem to.)
“The evolutionary disadvantage is that wound healing is slowed,” Dr. Fuchs said, but humans also gained evolutionary advantages by losing hair.
“They can put on a coat if they need to,” she added.
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Feeling lonely may take a toll on older adults’ memory — but it may not speed up cognitive decline, according to a new study.
Researchers from Colombia, Spain and Sweden analyzed data from more than 10,000 adults ages 65 to 94 across 12 European countries and found those who reported higher levels of loneliness did worse on memory tests at the start of the study, according to research published this month in the journal Aging & Mental Health.
Over a seven-year period, however, memory decline occurred at a similar rate regardless of how lonely participants felt.
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“The finding that loneliness significantly impacted memory, but not the speed of decline in memory over time was a surprising outcome,” lead author Dr. Luis Carlos Venegas-Sanabria of the School of Medicine and Health Sciences at the Universidad del Rosario said in a statement.
Loneliness may be linked to memory performance in older adults, a new study suggests. (iStock)
“It suggests that loneliness may play a more prominent role in the initial state of memory than in its progressive decline,” Venegas-Sanabria said, adding that the findings highlight the importance of addressing loneliness as a factor in cognitive performance.
The findings add to debate about whether loneliness contributes to dementia risk. While loneliness and social isolation are often considered risk factors for cognitive decline, research results have been mixed.
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The study looked at data from the long-running Survey of Health, Ageing and Retirement in Europe (SHARE), which tracked 10,217 older adults between 2012 and 2019. Participants were asked to recall words immediately and after a delay to measure memory performance.
Social isolation and loneliness could play a surprising role in cognitive health among seniors. (iStock)
Loneliness was assessed using three questions about how often participants felt isolated, left out or lacking companionship.
About 8% of participants reported high levels of loneliness at the outset. That group tended to be older, more likely to be female and more likely to have conditions such as depression.
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Researchers found that those with higher loneliness had lower scores on both immediate and delayed memory tests at baseline. Still, all groups — regardless of loneliness level — experienced similar declines in memory over time.
The results suggest loneliness may not directly accelerate the progression of memory loss, though it remains linked to poorer cognitive performance overall.
Researchers look at a brain scan at the National Institutes of Health in Bethesda, Maryland. (Saul Loeb/AFP/Getty Images)
Experts warn, however, that the findings should not be interpreted to mean loneliness is harmless.
“The finding that lonely older adults start with worse memory but don’t decline faster is actually the most interesting part of the paper, and I think it’s easy to misread,” said Jordan Weiss, Ph.D., a scientific advisor and aging expert at Assisted Living Magazine and a professor at NYU Grossman School of Medicine.
“It likely means loneliness does its damage earlier in life, well before people show up in a study like this at 65-plus,” Weiss told Fox News Digital.
By older age, long-term social patterns may already be established, making it harder to detect when the effects of loneliness first took hold, an aging expert says. (iStock)
He suggested that by older age, long-term social patterns may already be established, making it harder to detect when the effects of loneliness first took hold.
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“By the time you’re measuring someone in their late 60s, decades of social connection patterns are already baked in,” he said.
Weiss, who was not involved in the research, added that loneliness may coincide with other health conditions, and noted that participants who felt more isolated also had higher rates of depression, high-blood pressure and diabetes. The link, he said, may reflect a cluster of health risks rather than a direct cause.
“While they can go hand-in-hand, it’s not clear that loneliness contributes to dementia,” a psychotherapist says. (iStock)
Amy Morin, a Florida-based psychotherapist and author, said the findings reflect a broader pattern in research on loneliness and brain health, and that the relationship may be more complex than it appears.
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“The evidence shows there’s a link between loneliness and cognitive decline but there’s no direct evidence of a cause and effect relationship,” she said. “So while they can go hand-in-hand, it’s not clear that loneliness contributes to dementia.”
Morin added that loneliness, which can fluctuate, may not be the root of the problem, but rather a symptom of other underlying mental or physical health issues.
Researchers suggested screening for loneliness be incorporated into routine cognitive assessments as one way to support healthy aging. (iStock)
She said staying socially and mentally engaged is crucial for overall brain health.
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“It’s important to be proactive about social activities,” Morin said. “Joining a book club, having coffee with a friend, or attending faith-based services can be a powerful way to maintain connections in older age.”
The researchers also suggested screening for loneliness be incorporated into routine cognitive assessments as one way to support healthy aging.
Fox News Digital reached out to the researchers for comment.
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Research continues to uncover new details on how fasting may help extend life.
A new study published in the journal Nature Communications investigated how intermittent fasting can boost longevity in small worms often used in aging research.
Researchers from the University of Texas Southwestern Medical Center in Dallas compared worms that were fed normally to those that underwent a 24-hour fast in early adulthood and were then fed again, according to a press release.
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The scientists measured a variety of factors, including stored fat, gene activity related to fat metabolism and lifespan.
The results showed that the life-boosting benefit did not depend on the fasting itself but on the body’s behavior after eating again.
Experts say sustainability is key when choosing a long-term weight-loss strategy. (iStock)
Study lead Peter Douglas, associate professor of molecular biology and a member of the Hamon Center for Regenerative Science and Medicine at UT Southwestern, suggested that these discoveries “shift the focus toward a neglected side of the metabolic coin – the re-feeding phase.”
“Our data suggest that the health-promoting effects of intermittent fasting are not merely a product of the fast itself, but are dependent on how the metabolic machinery recalibrates during the subsequent transition back to a fed state,” he said.
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“Our findings bridge a gap between lipid metabolism and aging research,” he added. “By targeting aging, the single greatest risk factor for human disease, we move beyond treating isolated conditions toward a preventive model of medicine that enhances quality of life for all individuals.”
Lauri Wright, director of nutrition programs at the University of South Florida’s College of Public Health, called this a “high-quality” study that adds an “important nuance to how we think about fasting and longevity.”
Intermittent fasting typically involves limiting meals to an eight-hour daily window or fasting every other day. (iStock)
The benefits of the refeeding phase after fasting were “especially interesting,” Wright, who was not involved in the study, told Fox News Digital.
“The researchers showed that longevity was linked to the body’s ability to turn off fat breakdown after fasting, allowing cells to restore energy balance,” she reiterated.
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“From a scientific standpoint, that’s a meaningful shift because it suggests fasting is not just about burning fat, but about metabolic flexibility.”
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Fasting may support longevity through triggering metabolic switching, enhancing cellular repair and stress resistance and improving markers like insulin sensitivity, research shows.
Limitations and cautions
Although this study provides “important insight” on the power of refeeding, Wright noted that the findings should be approached with caution, as the study was done on worms and cannot always be translated to humans.
“Additionally, it explains how a process might work in a controlled lab condition rather than real-world eating behaviors,” she added as a limitation. “Finally, the study is short-term and doesn’t give us the long-term translation on lifespan outcomes.”
The review found intermittent fasting was barely more effective than doing nothing, according to the study authors. (iStock)
Wright cautioned that fasting is “not a magic solution for longevity, and how you eat overall matters more than when you eat.”
“I advise, first and foremost, to focus on diet quality, including a variety of fruits and vegetables, healthy fats and minimally processed foods,” she said.
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For those who are considering fasting, it’s better to stick with a moderate plan — like a 12- to 14-hour overnight fast — rather than going to extremes, Wright said. After fasting, she recommends focusing on well-balanced meals.
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Several groups of people should be cautioned against fasting, according to Wright, including those with diabetes who are on insulin or hypoglycemic medications, those who are pregnant or breastfeeding, anyone with a history of eating disorders and older adults at risk of malnutrition.
Anyone considering intermittent fasting should consult with a doctor before starting.
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