Biological Classification

Biological classification, also called taxonomy, is the branch of biology that arranges living things into groups based on shared characteristics and evolutionary relationships. Its purpose is to establish a consistent system for naming and distinguishing the organisms of the world.

The modern system uses hierarchical ranks: kingdom, phylum, class, order, family, genus, and species. Each rank has a two-part Latin name, with the genus name followed by the species name.

Binomial Nomenclature

The system of binomial nomenclature was made famous by the Swedish biologist Carl Linnaeus in the 18th century. The first name is the genus, which begins with a capital letter; the second is the species name, written in lowercase. Both are typically printed in italic type. International rules govern how names are accepted, to prevent one species from having two different names.

Ranks and Groups

Intermediate ranks such as subspecies, subfamily, and superorder are used when needed. The major kingdoms recognized today include animals, plants, fungi, and single-celled organisms; some modern schemes further divide these into three domains called Bacteria, Archaea, and Eukarya. This division is not universally agreed upon and changes as new scientific findings emerge.

The Basis of Evolutionary Relationships

Historically, classification relied on visible, structural features: body form, bone structure, organs, and skin. Today, DNA evidence is included, making it possible to measure how closely related organisms are. This approach is called phylogenetics, and it often results in previously accepted groups being split or merged.