Organizing Microbial Diversity and Interspecies Relations through Diagrams: Trees, Maps, and the Visual Semiotics of the Living

This paper aims to understand how and why tree diagrams are of central importance to microbiome scientists in their practices of meaning making. The interfaces that scientists use are, in fact, topological structures that organize the genetic data generated by sequencing technology. They establish relationships among microbes and also between microbes and the conditions of the ecological niche they help construct. The tree structure is a powerful topos of knowledge organization in Western culture. However, biomolecular research has revealed the existence of horizontal gene exchange among microbes and other merging forms; these cast doubt on the tree as a valid representational metaphor for the tangle of the microbial world and help to overcome neo-Darwinism. This essay analyzes the software and interfaces used by microbiome scientists as tools for organizing knowledge that shape how we see human-microbe relationships, while escaping a representational function. While trees have long been considered representative forms of visualization of an evolutionary paradigm, we emphasize the non-illustrative and heuristic power of these interfaces, which, although steeped in centuries of reflection and debate on evolutionary theories, respond more to a diagrammatic logic: tools for discovering the new from genetic “black matter” and for exploring new forms of relationships between microbes and humans.