Cladistics is a method of biological classification that systematically organizes species into groups called clades. Cladistics was introduced by the biologist Willi Hennig in 1950 and has become the dominant method of phylogenetic analysis (evolutionary relationships between organisms) in the 21st century.

Cladistics differs from Linnaean taxonomy, which groups organisms according to overall similarity and typically employs phenetic characters (traits that are shared among many species). Phylogenetic systematics, on the other hand, works from the assumption that related organisms will have a more similar evolutionary history than unrelated organisms; thus phylogenetic systematics relies on parsimony (the principle of Occam’s razor) to infer the most parsimonious tree for explaining relationships among organisms based on similarities in their traits.

Cladistics can be used to determine which traits are ancestral and which are derived (or newer features), which helps scientists infer evolutionary relationships among organisms. A cladogram is an illustration of these relationships with branches representing lineages that split over time, with each branch point representing an evolutionary change (e.g., speciation).

Last modified: September 25, 2022