Taxonomy

Taxonomy is the branch of biology that discovers and describes organisms, gives them scientific names and sorts them into groups. Its system is hierarchical: each group sits inside a larger, more inclusive one. Working upward from the narrowest, the main ranks are species, genus, family, order, class, phylum, kingdom and domain. A wolf, for example, belongs to the domain Eukarya, kingdom Animalia, phylum Chordata, class Mammalia, order Carnivora, family Canidae and genus Canis. A named group at any rank is called a taxon (plural taxa).

The Swedish naturalist Carl Linnaeus set out this ranked scheme in the 1700s, together with two-part species names. He grouped organisms by visible features, and some of his groupings, such as sorting plants by counting their stamens and pistils, were artificial. Today taxonomists aim for groups that reflect evolutionary relationships, using DNA as well as anatomy and fossils, so phylogenetic trees built by the related field of systematics now shape classification. As new evidence appears, organisms are sometimes moved between groups or renamed.

Taxonomy matters well beyond museums: a stable name lets a doctor, an ecologist and a genetic database all refer to the same pathogen, crop pest or endangered species.