Conceptual Parallels: Microbiome Research and Ancient Medicine

The concepts currently operating in much medical microbiome research bear a curious resemblance to an ancient tradition of Western medicine. This tradition, humoral medicine, is concerned with the four humors: yellow and black bile, phlegm, blood. Both humoral medicine and medical microbiome research use notions of imbalance and balance for broad explanations of disease and health. Both traditions also hold that the composition of humors or microbiomes determines bodily as well as mental states. Causality in each system is often conceived teleologically, meaning that humors or microbiomes "function for" the maintenance of the whole. And ultimately, each framework situates the humors or microbiomes in a multilevel interactionist theory that conceptualizes individual health within a broader environmental context. As well as critically assessing the parallels between these systems, this article sketches some explanations of how they may have arisen. The authors also evaluate the implications of these similarities for the future of medical microbiome research and suggest ways in which the field might move forward.