That scratch on your arm, that scrape on your knee — they’re taking their sweet time to heal, and it’s likely the fault of your fur, or, really, your lack thereof. Testing the speed of skin healing in an assortment of animals, a team of researchers has found that skin takes a lot longer to heal in humans than it does in other primates and mammals.
Publishing their results in a study in the Proceedings of the Royal Society B: Biological Sciences, the researchers say that the reason may be because of the loss of fur in humans around 2 million years ago.
“Human wound-healing rates were found to be markedly slower,” the researchers report in their study. In fact, the rates were “approximately three times slower than those observed in non-human primates.”
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A Slower Speed of Skin Healing
Researchers have long suggested that humans take more time to heal than other mammals. But, thus far, the research hasn’t had all that much to say about whether the slow healing of skin in humans is unique to humans or shared with other primates, too.
“Human wound healing occurs slowly, and it remains unclear whether this characteristic is unique to humans,” the researchers write. “To address this issue, it is necessary to first clarify whether slow wound healing is … a common characteristic of primates.”
Attempting to find that out, a team of researchers conducted a series of experiments involving healing in humans, other primates, and other mammals. Comparing skin wounds in humans with skin wounds in other primates (including chimpanzees, baboons, and two types of monkeys), as well as with skin wounds in other mammals (such as mice and rats), the researchers found that humans had a significantly slower rate of healing. While they healed at a rate of around 0.25 millimeters of skin a day, the other primates and mammals healed at a rate around three times that.
“This finding indicates that the slow wound healing observed in humans is not a common characteristic … and highlights the possibility of evolutionary adaptations in humans,” the researchers write.
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Shedding Fur for Sweat and Slow Healing
Indeed, the fact that the slow healing seen in humans is not seen in other primates indicates that the trait is a relatively recent adaptation, acquired after the emergence of the last common ancestor of humans and other primates.
“This observation implies that the slower wound-healing rate in humans may have evolved at a certain point within the human lineage,” the researchers write.
Intriguingly, it is possible that humans have slower skin healing than other primates because humans traded their fur for sweat glands around 2 million years ago, resulting in fewer hair follicles and thicker skin. Since hair follicles contain stem cells that support skin healing, fewer hair follicles could translate into fewer stem cells and a slower mending of scrapes and scratches in humans. Moreover, since fewer hair follicles means more exposure of the skin to the environment, humanity’s move from furry to smooth could’ve also meant a transition towards thicker (and thus slower-healing) skin, as more skin may take more time to heal.
The researchers write that the human skin is three to four times thicker than the skin of other primates, a factor that could “contribute to the slower wound-healing rate observed in humans.”
Swapping fur for sweat glands may seem silly, as it substituted a faster system of healing for a slower system. But the study stresses that humanity’s sweat glands brought their own benefits, too, providing humans with a better strategy for cooling off their brains and bodies. So, the next time you have a scratch or a scrape that won’t heal, consider the trade-off. Would it be better to be a whole lot furrier and a whole lot hotter, too?
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Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Proceedings of the Royal Society B: Biological Sciences. Inter-Species Differences in Wound-Healing Rate: A Comparative Study Involving Primates and Rodents
Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.
