This commentary [attached] is enjoyable to mull over. In just this past decade, the “gut-brain-microbiome” has been exploding in significance and challlenging many concepts that clinical medicine has held for decades. Previously, we humans have always considered ourselves to be individuals, based on our own DNA and chromosomes. And our genomes contained, or 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, which would have seemed so improbable a decade ago. This change has to do with the enormous amounts of bacterial colonies that live in our intestines. It has been known, since invention of the microscope by van Leeuwenhoek in the 17th century, that animals, including humans, are hosts to many microorganisms. However, until recently these microorganisms were generally treated as either pathogens or as insignificant; in fact, the absence of microbes was equated with better health.
This classical understanding of microbes has been called into question, due to low-cost high-throughput gene-sequencing techniques, that has enabled us to study microbial communities without the need to grow them in a Petri dish. There is now overwhelming evidence that normal development, as well as the maintenance of any animal having a gut, depends upon our microbiome. Humans are not a unitary entity, but rather a dynamic and interactive community of human cells and microbial cells. By current estimates, approximately half of the cells in our body are microbial. Studies of the microbiome are leading to a major reassessment of biological processes –– as varied as the physiological function of specific organs, composition of metabolites in body fluids, and management of transmissible diseases.
Evidence now shows that our resident microbes orchestrate the adaptive immune system, influence the brain, and contribute more gene functions than our own genome. 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, these conseuences call 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.”
PLoS Biol Feb 2o18; 16: e2005358