Our capacity to command fire separates humankind from apes, fueling both our cultural and biological advancement, and rapidly propelling us into the space age. Nevertheless, playing with fire carries the risk of getting burned, and researchers now posit that the fiery missteps and resulting injuries sustained by our ancestors may have played a role in shaping our immune systems. The findings of this study are featured in the journal BioEssays.
“The mastery of fire is deeply embedded in the human experience—from our preference for cooked food and boiled drinks to the technologies that define the modern world,” stated study author Joshua Cuddy. “Consequently, unlike any other species, most humans will incur burns repeatedly throughout their lives, a pattern likely dating back over a million years to the earliest uses of fire.”
To illustrate this point, the researchers mention that even while composing their paper, one of the authors unfortunately experienced a burn to the lower lip—painful, silly, but not fatal—from biting into a piece of chicken Kiev still dripping with melted butter. Intriguedly, they go on to explain that the human immune system responds to thermal injuries in a distinctly different manner compared to other trauma, such as cuts.
For instance, they observe that burns trigger an “intensified inflammatory phase,” mediated by the release of pro-inflammatory signaling molecules known as cytokines. This heightened response is crucial because fire inflicts more extensive tissue damage than incisions, leading to a higher vulnerability to infection. Without such a robust immune mobilization, even minor burns could potentially become life-threatening.
Thus, the researchers hypothesize that trauma resulting from fire exposure might have driven the evolution of these specific immune responses, as the survival of our species depended on our ability to effectively mend persistent burn wounds. To investigate this, they commenced by contrasting the gene expression profiles (transcriptomes) of burned versus unburned skin, pinpointing 94 different genes that become activated as part of the response to heat-induced injury.
Subsequently, when these genes were compared against those identified in chimpanzees, gorillas, orangutans, and macaques, the study authors discovered that at least nine and potentially as many as 19 of these genes exhibit evidence of accelerated evolution in humans. These include genes that increase the skin’s propensity for scarring, as well as others that cause heightened pain sensitivity in recently burned skin, thereby encouraging us to protect the wounds and prevent further damage.
“Our research suggests that natural selection favored traits that improved survival following small and frequent burns,” asserts Cuddy. “However, these same adaptations may have come with evolutionary trade-offs, helping to explain why humans remain uniquely susceptible to complications from severe burns.”
For example, the increased proclivity for inflammation and scarring after a burn can escalate into systemic inflammatory response syndrome or, in severe instances, organ failure.
Commenting on the significance of these findings, study co-author Professor Armand Leroi explained that the concept of “burn selection” theory “represents a novel mechanism of natural selection—one that is, moreover, dependent on culture. It is woven into the fabric of what makes us human, an aspect we previously overlooked.”
Furthermore, given that the genes responsible for enhanced burn healing were not detected in orangutans, perhaps King Louis should indeed stick to cooler meals.
About the Author
