Microbiome: How the microbes living in your body challenge the idea of what it means to be human

YOU may, quite reasonably, think you are an individual of the species Homo sapiens. Once you have finished reading what follows, you will hopefully have been convinced that there is far more to us than that. Trillions of other organisms live on (and, more notably, in) your body. As you will see in the reports that follow, their impact on you is such that you will probably never think about yourself in the same way again. Your microbes change who you are and what it means to be you. With knowledge of this facet of ourselves growing rapidly, exploring it has never been more relevant.

Until recently, scientists believed that there were three discrete parts of our nature that reflected solid aspects of an individual self: the immune system, the genome and the brain. “None of these pillars of the traditional definitions of the self – immunity, genome integrity, the central nervous system – are free of microbial impact,” says Thomas Bosch at Kiel University in Germany.

The microbes that colonise us, collectively known as the microbiome, challenge the concept of a discrete self. These include bacteria, viruses and fungi, although the bacteria are the best-studied. Together, these microbes orchestrate the immune system, influence how the brain works and grows, and affect our personality and feelings. Over a third of the genes in the human genome have a bacterial origin, and the action of trillions of microbial genes in the gut has direct impacts on our nutrition and …