The basic context in which evolutionary biology works is phylogeny, a system of classification based on evolutionary relationships rather than phenotypic similarity. The central tenet of evolution is that all life is derived from a single common ancestor, and all life is therefore related. The process by which living things have diverged to the staggering diversity on this world is through the divergence of populations into separate species, which in turn give rise to more distant cousins through time.
We express the relationships among groups of organisms through diagrams called cladograms. If the common ancestor is known and included in the depiction and the depiction includes an axis of time, it is referred to as an evolutionary tree.