Humans heal from wounds at one-third the rate of other mammals, a surprising evolutionary trade-off that scientists believe may be linked to our unique sweaty, hairless skin and advanced cognitive development.

At a Glance

  • Human wounds heal at approximately 0.25 millimeters per day, compared to 0.61 millimeters in other mammals including our closest relatives, chimpanzees
  • The slower healing is likely an evolutionary trade-off that developed after humans diverged from our common ancestor with chimpanzees
  • Scientists believe this adaptation may be related to our naked, sweaty skin that evolved to cool our large brains
  • Social support mechanisms like food sharing and medicine may have compensated for humans' slower physical recovery
  • Further research is needed to understand the genetic and cellular causes behind humans' delayed wound healing

The Surprising Healing Gap

A groundbreaking study published in Proceedings of the Royal Society B has revealed that human wounds heal at less than one-third the rate of other mammals, including our closest relatives. Researchers found that while chimpanzees, baboons, monkeys, mice, and rats all heal at a similar rate of about 0.61 millimeters per day, human wounds from similar injuries heal at just 0.25 millimeters daily. This stark difference suggests that slower healing in humans likely evolved after we diverged from our common ancestor with chimpanzees, indicating a relatively recent evolutionary adaptation.

The study involved 24 human patients with skin tumors and several animal species, including captive chimpanzees and wild baboons. Researchers created controlled wounds or observed natural injuries and measured healing rates across species. Remarkably, they found no significant difference in healing rates among the non-human primates, rats, and mice studied—only humans showed dramatically slower recovery times. This consistent healing rate across diverse mammals suggests an evolutionarily optimal recovery speed that humans no longer share.

Sweaty Skin and Slower Healing

The most compelling explanation for humans' slower healing involves our distinctive skin characteristics. Unlike our furry relatives, human skin has smaller hair follicles but significantly more sweat glands. This adaptation allows us to cool through perspiration, a crucial development that supported our species' endurance running capabilities and, more importantly, helped maintain optimal temperature for our large, energy-intensive brains. The trade-off for this cooling mechanism appears to be compromised wound healing.

The evolutionary biology behind this trade-off makes logical sense. Our ancestors developed social structures, clothing, and eventually medicine that compensated for slower physical recovery. Meanwhile, the advantages of advanced cognitive function and temperature regulation through sweating provided significant survival benefits that outweighed the disadvantages of slower healing in increasingly complex social environments.

Social Support and Survival

Researchers suggest that humans' slower healing may have become viable thanks to developing social support systems. Archaeological evidence indicates that even our ancient ancestors like Homo erectus and Neanderthals cared for injured group members. Food sharing, nursing of the injured, and eventually the use of medicinal plants likely mitigated the evolutionary disadvantage of delayed wound healing, allowing the trait to persist despite potential survival drawbacks.

The research team also points to other potential factors that might explain humans' slower healing, including the possibility that we developed thicker skin for protection. However, they emphasize that a comprehensive understanding requires further investigation. "A more comprehensive understanding of the underlying causes of delayed wound healing in humans requires a comprehensive approach that integrates genetic, cellular, morphological, fossil human skeletal and extant non-human primate data," the authors conclude.