If you’ve ever had an injury, especially one that impacts the way that you live your life, you’ll know how painfully long it seems to take to heal.

Whether it’s a burn or a broken bone, a wound or an incision, these things cause us pain that reminds us of the injury for quite some time, with the severity of the injury usually correlating with the length of time that healing takes.

For example, while a papercut takes on average of two to three days to heal, a torn anterior cruciate ligament (ACL – the bane of a soccer player’s injury list) takes between six and twelve months to heal fully. A broken nose takes around three or four weeks, but the internal healing from a caesarean section can take months.

However, if you’ve ever had a pet that has had surgery, you’ll have marvelled at how they’re up and about by the end of the day, while we are confined to our hospital beds for days after equivalent procedures.

And according to new research from Japanese scientist Professor Akiko Matsumoto-Oda, this is something quite unique to humans, with a much longer healing period a result of our unique evolution.

Recently published in the academic journal Proceedings of the Royal Society B, the team led by Matsumoto-Oda explored the healing processes of Kenyan baboons after noticing that the monkeys’ wounds healed much faster than injuries sustained by humans.

Matsumoto-Oda’s work ruled out the long-held suspicion that our slower healing rate was common amongst primates. She and her team compared the healing rate of 24 human patients after the removal of skin tumors with the healing rates of various mammals and primates, including chimpanzees, rats, mice, and baboons.

Though some of the wounds on the chimpanzees occurred from their natural behaviors (including fighting), most of the wounds were inflicted upon the animals whilst under anaesthetic.

Incredibly, whilst human wounds healed at an average rate of 0.25 millimeters per day, those on animals healed at an average of 0.61 millimeters per day.

Ordinarily in the animal kingdom, a slow rate of healing would be detrimental to survival since it would impact an individual’s ability to outrun predators and catch prey.

According to the researchers, our slow rate of wound healing is evidence of evolutionary changes that happened to humans at some point in our lineage. As they explain in their paper, this evolutionary disadvantage would not always have been the case, and is likely a result of many societal factors that we have gradually put in place:

“This finding indicates that the slow wound healing observed in humans is not a common characteristic among primate order and highlights the possibility of evolutionary adaptations in humans.

Additionally, even though controversial, it is possible that the development of social support for older and disabled individuals in the human lineage, as well as the use of medicinal plants, mitigated the evolutionary disadvantage of delayed wound healing.”

Even more incredibly, they suggest that it could have been changes to our skin that is at the root of this change. That’s because we have thicker skin, thanks to our lack of fur and evolutionarily-acquired sweat glands. Though these factors have been an important part of our adaptations, they take longer to heal.

And thanks to our place at the top of most food pyramids, humans are able to rest up and heal over time, a luxury that our primate cousins are not allowed.

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