The image of the tree, of branching phylogenies, has come to underly all our thinking about organisms and evolution. It is a "canonical icon" whose influence can be described as an " unconscious hegemony."The hierarchical structure expresses the pattern of branching speciation, of successive, unending, natural wedging through natural selection which forms the "tree of life." The tree combines the "ladder" of evolution, from lower to higher lifeform -- and with man at the top -- with the "cone" of increasing diversity. (Steven Jay Gould in Hidden Histories of Science) As Gould points out, the latter is factually incorrect. The Cambrian explosion was the moment of greatest diversity. The former is, of course, an anthropocentric bias.
Historical narratives unfold like trees.
Christopher Alexander's Notes on the Synthesis of Form is an attempt to reach fitness of object and context through the hierarchy of the tree. For Alexander, the tree" gives an explicit description of the structure implicitly responsible for the success and stability of the unselfconscious form-making process." and "gives the strongest possible decomposition of the problem that does not interfere with the task of synthesizing it parts in a unified way." According to Alexander, The tree diagram shows "natural clusters" which he calls the "program." The analytic stage of design thus yields the tree of sets of requirements. In the synthetic stage, a diagram is made for each of these subsets which are then realized in the form. (see arch theories )
The fundamental purpose of Alexander's undertaking is to correlate the hierarchical analysis of the functional problem with a synthetic hierarchy of diagrams that combine into the form. "The hierarchical compostion of these diagrams will then lead to a physical object whose structural hierarchy is the exact counterpart of the functional hierarchy established during the analysis of the problem." (p.131)
Subsequently, Alexander proposed the semilattice as alternative to tree structure. (see rhizome.)
"The trial is a process whose global balance sheet can easily be recorded. It consists of an ordered structure with given axioms, a structure that branches out in several models: the social tree, the tree of the production of energy, of entropy, and of pollution, the tree of causes, the hydrographic tree, the tree of the "better", the tree of good, evil, and knowledge--and a tree in general. All these trees together make a forest, into which 'The Wolf carries the lamb off and then eats him.' This is not demonstrated by an order (proces ) between that which precedes and that which follows, but shown as a forest of models, a forest of symbols. The proof is only one process among others: there exist philosophers from whom a whole forest is hidden by a single tree." (Michel Serres, Hermes, p. 19)