Darwin and the Tree of Life: the roots of the evolutionary tree NILS PETTER HELLSTRO ¨ M Department for History of Science and Ideas, Uppsala University, Box 629, 75126 Uppsala, Sweden (e-mail: petter.hellstrom@idehist.uu.se). ABSTRACT: To speak of evolutionary trees and of the Tree of Life has become routine in evolution studies, despite recurrent objections. Because it is not immediately obvious why a tree is suited to represent evolutionary history – woodland trees do not have their buds in the present and their trunks in the past, for a start – the reason why trees make sense to us is historically and culturally, not scientifically, predicated. To account for the Tree of Life, simultaneously genealogical and cosmological, we must explore the particular context in which Darwin declared the natural order to be analogous to a pedigree, and in which he communicated this vision by recourse to a tree. The name he gave his tree reveals part of the story, as before Darwin’s appropriation of it, the Tree of Life grew in Paradise at the heart of God’s creation. KEY WORDS: evolutionary theory – tree imagery – science and culture – science and religion – science and society. INTRODUCTION In On the origin of species, Charles Darwin (1859: 129–130) evoked an arresting image of a tree struggling with itself. The image was vivid and violent, orderly and chaotic: twigs and branches killed each other for space and survival, but simultaneously yielded beauty and “the classification of all extinct and living species in groups subordinate to groups”. Darwin’s tree, in effect, was a family tree of all life, in which the buds were individuals and the branches their ancestral lineages. “As buds give rise by growth to fresh buds”, Darwin wrote, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications. This peculiar tree had matured in Darwin’s mind for more than 20 years. In his notebooks on transmutation from the late 1830s, written before he developed his theory of descent by natural selection, he had invoked the Tree of Life to visualize the interconnected history and classification of living beings. From this first appearance, there existed a curious, if unstated, relationship between text and diagram; three ramifying sketches of evolutionary development followed the first mentions of the “tree of life” in the 1837 notebook (Barrett et al. 1987: 177, 180), and a branching diagram appeared shortly before the Tree of Life passage in Origin (Darwin 1859: between 116 and 117). Darwin, however, was not first to speak of the Tree of Life. Originally native to biblical Paradise, it was one of many trees that for centuries had been part of religious imagery. Archives of natural history 39.2 (2012): 234–252 Edinburgh University Press DOI: 10.3366/anh.2012.0092 # The Society for the History of Natural History www.eupjournals.com/anh