How the microbiome challenges our concept of self

Today, the three classical biological explanations of the individual self--the immune system, the brain, the genome--are being challenged by the new field of microbiome research.Evidence shows that our resident microbes orchestrate the adaptive immune system, influence the brain, and contribute more gene functions than our own genome.The realization that humans are not individual, discrete entities but rather the outcome of ever-changing interactions with microorganisms has consequences beyond the biological disciplines.In particular, it calls into question the assumption that distinctive human traits set us apart from all other animals--and therefore also the traditional disciplinary divisions between the arts and the sciences. Challenges to the classical biological explanations of the individual selfAre we humans really the individual, bounded selves we take ourselves to be? Until recently, little seemed more obvious to both the natural and the human sciences.The former found the material basis of the individual human self in the adaptive immune system, the brain, and the genome sequence, and the latter catalogued the many different ways in which humans-across time and space-have learned to make sense of what it means to be an individual self.The discrete self was a philosophical certainty in both the natural and the human sciences.Today, this philosophical certainty--and therefore our sense of self--faces major challenges [1][2][3][4].The source of this challenge is at first sight improbable: the study of microorganisms.It has been known from the inception of microbiology as a discipline in the 19th century (and arguably back to the invention of the microscope by van Leeuwenhoek in the 17th century) that animals, including humans, bear many microorganisms.Until recently, however, these microorganisms were generally treated as either pathogens or as insignificant: the absence of microbes was equated with health.This classical understanding of microbes has been called into question with the recent emergence of low-cost, high-throughput gene