Inter-species differences in wound-healing rate: A comparative study involving primates and rodents

Injuries, which affect survival and biological functioning, are common in the animal kingdom. This study systematically investigated whether the slow wound healing observed in humans is a unique characteristic within the primate order. First, we found no significant difference in wound-healing rates between baboons under experimental conditions and those in their natural environment (0.613 mm/day). Second, comparisons among four non-human primates (velvet monkeys, Sykes' monkeys, baboons, and chimpanzees) revealed no significant differences in wound-healing rates. Furthermore, these rates showed no significant differences compared to those observed in rodents, suggesting a potential commonality in wound-healing rates across diverse animal species. In contrast, human wound-healing rates were found to be markedly slower (0.25 mm/day), approximately three times slower than those observed in non-human primates. 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. Understanding these interspecies differences in wound-healing rates may provide valuable insights into the evolutionary implications of wound healing. This study also underscores the need for further research into the biological processes underlying wound healing in various species.

Methods
Subjects:

Cercopithecines: Three non-human primates in captivity were used: anubis baboons (n = 6), Sykes' monkeys (n = 5), and vervet monkeys (n = 6). All animals were anaesthetized, and full-thickness skin wounds (40 mm diameter) were created. The wounds were treated with gentamicin and covered for 1 day. Wound healing was monitored by photographing the wounds every 2–3 days. For wild baboons, data from Taniguchi and Matsumoto-Oda [16] were used for analysis.

Chimpanzees: Five captive adult chimpanzees (one female, four males) were used. Natural wounds were photographed at intervals of 2–7 days, and wound dimensions were measured using a ruler.

Humans: A total of 24 patients (14 females, 10 males, aged 25–99) were included. Wounds were photographed following skin tumor removal.

Rodents: Mice (BALB/c and Jcl:SD) and rats were anaesthetized, and their backs were shaved before creating wounds. Wounds were monitored at 1–2 day intervals.

Healing Rate: Wound healing distances were measured at multiple time points and analyzed using linear regression to determine healing rates. Measurements were taken using ImageJ software.

Statistical Analysis: Linear mixed models were used to analyze the data, accounting for random effects in repeated measurements. For humans, age-related effects on healing were also modeled. All analyses were performed using R software version 4.1.2.