Tree of Life

The tree of life refers to the phylogeny of all living organisms. The metaphorical view of the “tree of life” predates the technical view, which itself is somewhat metaphorical: owing to non-tree-like evolutionary phenomena such as horizontal gene transfer and hybridization, the “tree of life” is an imperfect conceptual representation of evolutionary history. Depictions of the tree of life as a phylogenetic concept tend to emphasize the high degree of complexity in the branching structure, with large numbers of closely placed branches — as in this California buckeye at the end of summer.

“The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was small, budding twigs; and this connexion 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.”

– Charles Darwin, The Origin of Species (1859, p. 129)

Interestingly, analogous to the conceptually prominent position of the tree of life in phylogenetics, two of the most prominently positioned trees on the Stanford campus, at the entrance to the main quad, are specimens of arborvitae – Latin for “tree of life.”