The evolutionary history of a species or group of related species is called its phylogeny. When the evolutionary history is diagrammed, it is shown in the shape of a tree that traces evolutionary relationships as they have changed over time. The reconstruction of phylogenetic history is part of the field of systematics. The diversity of the phylogenetic tree is a reflection of speciation.

A phylogenetic tree shows not only how closely related two groups are but also how once-related species evolved independently. The further back in time a group branched represents a greater amount of time for divergent evolution to occur. When systematists construct a phylogenetic tree, they consider as much data as possible. Whenever possible, they take the fossil record into account to identify when branching occurred. Scientists can compare ribosomal RNA or mitochondrial DNA of different organisms to...