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Tree-like visualizations have played a central role in taxonomic and evolutionary biology for centuries, and the idea of a “tree of life” has been a pervasive notion not only in biology but also in religion, philosophy, and literature for much longer. The tree of life is a central figure in Darwin’s Origin of Species in both verbal and visual forms. As one of the most powerful and pervasive images in biological thought, what conceptual and communicative work has it enabled? How have the visual qualities and elements of the tree form interacted with biological thinking over time? This paper examines the pre-Darwinian history of tree images, the significance of Darwin’s use of such images, and the development of tree diagrams after Darwin. This history shows evidence of four separate traditions of visualization: cosmological, logical-philosophical, genealogical, and materialist. Visual traditions serve as rhetorical contexts that provide enthymematic backing, or what Perelman calls “objects of agreement,” for interpretation of tree diagrams. They produce polysemic warrants for arguments in different fields. The combination of the genealogical tradition with the cosmological and the logical changed the framework for thinking about the natural world and made Darwin’s theory of evolution possible; the later materialist tradition represents the “modernization” of biology as a science.


visual rhetoric, tree diagram, evolutionary biology, enthymeme

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.


The authors would like to thank Jeanne Fahnestock, Will Kimler, Fred Gould, and one anonymous reviewer for their beneficial comments on previous iterations of this paper. Brian Wiegmann provided expert guidance on interpreting contemporary phylogenies. We are also grateful for financial support from the Department of English and Foreign Languages, Frostburg State University, Maryland, and the SAS Institute Distinguished Professorship at North Carolina State University for paying the permission fees required to reproduce four images.