Darwin’s idea of an evolutionary tree of life sprouted from this and other tree-sketches of his early notebooks (Notebook B, 1837), illustrating the way in which all species are connected by common descent. In On the Origin of the Species (1859), there is one “indispensable [illustration] to show the nature of the very complex affinities of past & present animals.” This illustration is a rather abstract shrub-like diagram that played a pivotal part in explaining his principle of “descent with modification by means of natural selection.”
Darwin’s tree of life grew out into the single most important plant-metaphor in the natural sciences. Although tree-diagrams were not new to the natural sciences, Darwin’s evolutionary tree challenged an important doctrine of natural philosophy. When Darwin published the Origin, the Aristotelian order of nature still held sway over Western thinking. The natural order was still depicted as a linear ladder (scala naturae) or “chain of beings”, ranging from the “lower” life forms (plants) to the “highest” life forms (humans). Darwin too found it difficult to distance himself from a ladder-like conception of nature. To this day evolution is still often depicted as a linear progressive process from lower to higher life forms. During this talk we will look at the development of “tree-thinking” in Darwin’s work and how it supplanted his “ladder-thinking”.
