The comparative analysis of living and fossil species, including their discovery, description, evolutionary relationships to other species, and patterns of geographic distribution.
Systematics can be divided into four major fields. Taxonomy, often equated with systematics, is the discipline concerned with the discovery, description, and classification of organism groups, termed taxa (singular, taxon). Classification is the clustering of species into a hierarchical arrangement according to some criterion, usually an understanding of their relationships to other species. Phylogenetic analysis, an increasingly important aspect of systematics, is the discovery of the historical, evolutionary relationships among species; this pattern of relationships is termed a phylogeny. The fourth component of systematics is biogeography, the study of species' geographic distributions. Historical biogeography examines how species' distributions have changed over time in relationship to the history of landforms, ocean basins, and climate, as well as how those changes have contributed to the evolution of biotas (groups of species living together in communities and ecosystems).
Systematic data and interpretations underlie progress in all of biology. An understanding of relationships, in particular, is fundamental for interpreting comparative data across different kinds of organisms, whether those data be morphological, physiological, or biochemical.
