New research suggests that recovery is slower in humans than in our closest relatives, despite there being no clear reason. (Photo credit: Maria Borisova via Getty Images)
Scientists say humans heal wounds much more slowly than other mammals, including our closest primates.
In a study published Tuesday (April 29) in the journal Proceedings of the Royal Society B: Biological Sciences, the researchers found that human wounds heal about three times slower than similar injuries in non-human primates such as chimpanzees (Pan troglodytes), which, along with bonobos (Pan paniscus), are our closest living relatives.
This difference in healing speed between humans and chimpanzees has not been observed in other primates, nor in non-human primates or other mammals such as rodents. The discovery suggests that at some point in our evolution, humans evolved slower healing.
“This finding implies that delayed wound healing, characteristic of humans, is not a general feature among primates and highlights the possibility of evolutionary adaptation in humans,” the study authors write in their paper.
The healing process in humans goes through several stages, starting with blood clotting to prevent blood loss, then immune cells such as neutrophils and macrophages rushing to the wound area to destroy bacteria and remove dead tissue and debris. Next, the body repairs the damaged tissue: fibroblast cells produce collagen, a protein that gives structure and strength; new blood vessels form to deliver nutrients; and skin cells move across the wound to close it.
Other mammals heal in much the same way we do, with a few differences. Some species — like rats, mice, horses, and cats — use a method called wound contraction, in which the edges of a wound are pulled together, like sewing.
In a new study, researchers examined differences in healing rates between humans, non-human primates and other mammals.
The researchers studied wound healing in olive baboons (Papio anubis), Sykes' monkeys (Cercopithecus albogularis), and vervet monkeys (Chlorocebus pygerythrus) that were captured from the wild and then housed at the Kenya Primate Research Institute. The primates were anesthetized and given a 1.6-inch (40-millimeter) wound, and the wound area, length, and width were measured daily thereafter.
Meanwhile, to assess wound healing in chimpanzees, the researchers analyzed photographs of natural wounds on five chimpanzees at Kyoto University's Kumamoto Nature Reserve in Japan.
The wounds were on the upper and lower extremities, back, buttocks, abdomen, face, and back of the hand, and were photographed at intervals of two to seven days. The rate of healing was also measured in humans and rodents. Twenty-four volunteers undergoing skin tumor removal surgery had their wounds photographed daily at the University of the Ryukyus Hospital in Japan. Wounds in rats and mice were created and monitored in the laboratory.
The researchers found that there was no statistically significant difference in wound healing rates among the four nonhuman primate species, and no difference between wound healing rates in primates and rodents. They also found that wound healing rates in humans were about three times slower than in nonhuman primates.
“These results indicate a uniform healing rate among cercopithecines [a group of Old World monkeys], which make up a large part of the primate order, and chimpanzees, which are genetically and phylogenetically the closest relatives of humans. This observation suggests that non-human primates share a common healing rate,” the researchers note.
The discovery implies that humans may have evolved slower recovery relatively recently, after diverging from our last common ancestor with chimpanzees 6 million years ago, according to the paper.
Sourse: www.livescience.com
