The Tree of Life

Phylogeny is the organizing principle of modern biological taxonomy, and a guiding principle of modern phylogeny is monophyly: a monophyletic group is considered to be one that contains an ancestral lineage and all of its descendants. Any such a group can be extracted from a phylogenetic tree with a single cut. The tree shown here provides a guide to the relationships among the major groups of the extant (living) organisms in the Tree of Life. We include three groups that are not believed to be monophyletic; these are designated with quotation marks. The tree does not include viruses or prions.