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A team of evolutionary scientists, dermatologists and wildlife specialists affiliated with several institutions in Japan, Kenya and France has found that human skin wounds take nearly three times as long to heal as they do in other primates. In their study, in the journal Proceedings of the Royal Society B: Biological Sciences, the group conducted experiments involving skin healing speed in humans and several other primates.

Prior research and anecdotal evidence suggest that other animals recover from skin wounds faster than humans. In this new effort, the research team sought to measure such differences.

The experiments involved comparing skin wounds in humans—courtesy of volunteers at a hospital undergoing skin tumor removal—and several primates. Wound healing pace in chimpanzees was measured by studying chimps housed at a sanctuary who endured skin wounds periodically due to fighting between males.

The team also measured the rate of wound healing in monkeys housed at a research institute in Kenya—there, olive baboons, Sykes' monkeys and vervet monkeys were given skin wounds while anesthetized.

In looking at the data, the researchers found that all the test subjects healed at nearly the same rate—0.62 millimeters of new skin growth a day—except for humans, who healed at an average of 0.25 millimeters per day. The researchers also tested mice and rats and found their healing rates were similar to those of non-human primates.

The research team suggests the reason for the difference lies in humans having lost their fur. They note that hair follicle stem cells can grow skin cells when needed. Humans have replaced most of their hair follicles with sweat glands, which also have stem cells that can grow into skin cells, but do so far less efficiently.

As humans lost their fur, the researchers note, they replaced them with sweat glands to prevent overheating. The trade-off was obviously worth it, or humans would be covered in fur today. They also note that the expanding brain may have helped along the way, providing humans with the ability to treat skin wounds in ways other animals cannot.

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