(A) Sketch of a phylogeny from Charles Darwin's “Notebook B” (1837–1838). (Reproduced with permission from the Syndics of Cambridge University Library.) (B) A portion of the phylogeny that later appeared as the sole figure in The Origin of Species (the version from the first edition is shown). (Reproduced with permission from John van Wyhe ed., The Complete Work of Charles Darwin Online [http://darwin-online.org.uk/]). Darwin seemed quite taken with the metaphor of a tree, and wrote “limbs divided into great branches…were themselves once, when the tree was small, budding twigs; and this connection of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups.” Note that Darwin drew his phylogenies like real trees, with roots at bottom and leaves at top. In contrast, the phylogenies elsewhere in this article (like most in the literature today) are drawn so that time proceeds either from left to right, or from top to bottom.
