A cautionary note for claims about the microbiome's impact on the "self"

In their essay, “How the microbiome challenges our concept of self,” Rees and colleagues [1] argue that recent discoveries about the microbiome have far-reaching effects on our understanding of self and what it means to be human. They claim these effects are so profound that they require a new mode of operation for the arts and humanities: “a breakdown of the anachronistic barriers between the natural and the human sciences”. While we strongly support interdisciplinary collaboration between the arts and sciences, the authors overinflate the microbiome’s influence in ways that are conceptually and empirically problematic.

The empirical problems come from statements about the microbiome’s causal power as a unitary entity, which we think need to be more carefully phrased. The conceptual problems turn upon the unsystematic way the authors talk about the “self”. Throughout the article, the meaning of “self” oscillates between three specific biological understandings defined by the authors and far less precise usage (e.g., in claims like “interactions with microorganisms define the individual human self,” “profound implications…for our philosophical comprehension of the human self,” or in the essay’s title, “How the microbiome challenges our concept of self”). The context in which these looser attributions of “self” are deployed suggests at least three additional understandings that are more commonly the subject of humanistic or psychological inquiry. By conflating these various interpretations of self, Rees and colleagues create the impression that the microbiome’s impact on one specific biological notion automatically entails a similar impact on all notions of self (or perhaps on some unified notion). But these entailments are neither obvious nor argued for.