04. Staphylococcus epidermidis and the Myth of Neutrality
Artwork by Galit Shachaf
In microbiology, we categorize symbiotic relationships into neat boxes: mutualism (both benefit), parasitism (one benefits at the other's expense), and commensalism (one benefits while the other remains unaffected).
But is true neutrality possible in any relationship? Or does this classification reveal more about our limited understanding than about reality?
After all, we tend to disregard things that we do not understand.
Throughout scientific history, we've repeatedly labeled phenomena we don't understand as "nothing" or "junk"—from non-coding DNA (once called "junk DNA") to the microbiome (once considered merely "commensal"). This pattern reveals a scientific hubris: assuming that what we can't measure or don't yet understand must be inconsequential.
The "Neutral" Microbes on Our Skin
Illustration of Staphylococcus epidermidis. source: www.scientificanimations.com
Our skin hosts approximately 10,000 bacteria per square centimeter, with Staphylococcus epidermidis being among the most abundant. Traditionally labeled a "commensal," S. epidermidis was thought to benefit from our body's warm environment and nutrients without affecting us in return.
But is this truly a one-sided relationship?
Recent research reveal that S. epidermidis actively shapes our immune system, protects against pathogens by producing antimicrobial peptides, and influences skin barrier function. In certain contexts, these same bacteria can become opportunistic pathogens and cause infections.
This spectrum of interactions—from beneficial to harmful—suggests that the "commensal" label oversimplifies a complex, dynamic relationship that shifts based on context, environment, and timing.
The Philosophical Problem with Neutrality
Alfred North Whitehead, a process philosopher, would call commensalism a "conceptual phantom"—an abstraction that fails to capture biological reality. Whitehead argued that reality consists not of static substances but of processes and relationships. In his framework, every entity continuously responds to and incorporates others, making true neutrality impossible.
When we label S. epidermidis as "commensal," we're creating an artificial snapshot of a constantly evolving relationship. The microbe and host are continuously influencing each other's states, even when these influences aren't immediately apparent to us.
Beyond Microbiology: The No Neutrality Rule
This principle extends beyond microbes to human relationships. Dynamic Systems Theory (DST) conceptualizes relationships as complex, self-organizing systems where individuals continuously adapt to each other. Even when we believe we're maintaining independence, the ongoing interaction reshapes our preferences and behaviors.
As Kyselo and Tschacher note: "The stability of such patterns of the self are constantly maintained and calibrated by external and system-inherent gradients, such that changes of gradients will generally change the self's whole landscape."
Pure Altruism – No One Likes a Martyr
Perhaps the most persistent myth in human relationships is the notion of pure altruism—the idea that we can give without receiving anything in return. We've all encountered (or been) the self-proclaimed martyr who insists they expect nothing for their sacrifices, yet subtly collects benefits like social capital, moral superiority, or identity reinforcement; or alternatively, accumulates a grudge.
This isn't cynicism—it's recognizing the complex, multi-layered nature of human interactions where no action exists in isolation from its effects on both parties.
Like our misunderstanding of "commensal" microbes, the martyr's claim of neutrality (giving without receiving) represents another conceptual phantom—an artificial construct that doesn't reflect the reciprocal reality of human connection.
Just as S. epidermidis inevitably influences its host environment, even the most selfless-seeming human actions create ripples of effect that return to the giver in some form.
Even pop culture recognizes this truth. In Friends episode "The One Where Phoebe Hates PBS," Joey challenges Phoebe to find a truly selfless good deed—one that provides absolutely no benefit to the doer. Like true commensalism, such actions prove elusive because every interaction leaves its mark, however subtle. Phoebe's struggle to perform a purely selfless act mirrors science's struggle to identify truly neutral biological relationships—both may be fundamentally impossible.
Conclusion
In both microbiology and human relationships, perhaps we should approach the concept of neutrality with humility, recognizing that absence of evidence is not evidence of absence. The microbial world teaches us that relationships are rarely static and never truly neutral—they're dynamic processes of continuous influence and adaptation.
What other "conceptual phantoms" might be limiting our understanding of the microbial world—and ourselves?