Taxonomy is the branch of biology concerned with identifying, describing, naming, and classifying organisms. It organizes biological diversity into recognizable groups, called taxa, using evidence from structure, behavior, genetics, and other characteristics. Taxonomy supplies the names and classifications through which information about organisms can be compared and communicated. Its scope overlaps with systematics, the broader study of biological diversity and relationships, and with phylogenetics, which investigates evolutionary history. (cbd.int)
Historical development
Organisms were classified long before modern evolutionary theory, but Carl Linnaeus established an especially influential framework in the eighteenth century. His Species Plantarum (1753) and the tenth edition of Systema Naturae (1758) helped standardize two-part scientific names for plants and animals. Linnaeus also arranged organisms in nested categories, providing a framework that later biologists modified rather than adopted unchanged. (linnean.org)
The theory of evolution associated with Charles Darwin changed the interpretation of classification. Similarities could be understood as evidence of common ancestry rather than merely convenient grounds for grouping organisms. Modern taxonomy consequently draws on evolutionary relationships, although historical names and ranked categories remain important components of its organization. (openstax.org)
Taxa and hierarchical classification
A taxon is a particular recognized group; a taxonomic rank specifies its level within a classification. Familiar ranks, from broader to narrower, are domain, kingdom, phylum, class, order, family, genus, and species. Additional ranks, such as subfamily and subspecies, allow finer distinctions. A family is therefore a rank, whereas a named family is a taxon occupying that rank. (openstax.org)
In the widely taught three-domain framework, cellular organisms are grouped into Bacteria, Archaea, and Eukarya, the domain containing eukaryotes. Nested classifications allow a species to be placed within progressively more inclusive groups. However, a rank-based hierarchy is not itself a complete representation of evolutionary history: branching relationships often require more detail than the conventional sequence of ranks provides. (openstax.org)
Scientific names and nomenclature
Binomial nomenclature gives a species a two-part scientific name, such as Homo sapiens. The first component identifies the genus; the second distinguishes the species within that genus. The genus begins with a capital letter and the second component with a lowercase letter. Both are conventionally italicized. The second component alone is not the complete species name. (code.iczn.org)
Biological nomenclature governs names, whereas taxonomy determines how organisms are delimited and classified. Separate codes apply to different groups, including animals, algae, fungi and plants, prokaryotes, and viruses. Naming rules do not ordinarily dictate which competing taxonomic interpretation must be accepted. (iczn.org)
Names are anchored through name-bearing types. In zoology, the type of a species-group name is a specimen or set of specimens that provides an objective reference for applying that name; it need not represent an average or especially typical individual. The principle of priority generally favors the oldest available name, subject to provisions and exceptions intended to preserve stability. Different names judged to refer to the same taxon are synonyms; identical names established for different taxa are homonyms. (code.iczn.org)
Species delimitation and taxonomic practice
Recognizing species requires distinguishing variation within a species from differences between species. Different species concepts emphasize different evidence. The biological species concept focuses on reproductive isolation, whereas morphological and phylogenetic approaches emphasize distinguishing traits or evolutionary lineages. These criteria may become evident at different stages of speciation, so they do not always produce identical boundaries. (pubmed.ncbi.nlm.nih.gov)
Taxonomic work commonly begins with collecting or examining specimens and comparing them with published descriptions and reference material. Researchers evaluate whether observed differences support an existing identification or a previously unrecognized species. A new-species description sets out distinguishing characteristics and establishes a name through publication under the applicable nomenclatural rules. Identification assigns a specimen to a recognized taxon; delimitation investigates the boundaries of the taxon itself. (cbd.int)
Evolutionary and molecular evidence
Cladistics reconstructs relationships using shared derived characteristics. It seeks to recognize clades, groups containing a common ancestor and all its descendants. Superficial resemblance alone can mislead classification because similar features may evolve independently, while close relatives may become markedly different. Anatomical and molecular evidence can therefore complement one another when reconstructing relationships. (openstax.org)
DNA data provide additional characters for comparing organisms. DNA barcoding uses standardized sequence regions to help identify specimens and detect candidate species. Its interpretation depends on reference identifications and on how sequence variation relates to species boundaries. A sequence difference does not automatically establish a new species, and a barcode is not a substitute for a formal taxonomic description. Integrative taxonomy combines molecular evidence with morphology, geography, behavior, or other independently informative data. (pmc.ncbi.nlm.nih.gov)
Applications and information resources
Taxonomy underpins inventories of biodiversity and supports conservation, environmental assessment, and the implementation of the Convention on Biological Diversity. Reliable identification allows observations from different places and studies to be associated with the same organisms. Gaps in descriptions, identification resources, collections, and expertise limit this work. (cbd.int)
Digital resources connect taxonomic names with biological records. The NCBI Taxonomy database, for example, curates organism names and classifications for public sequence databases. Such resources facilitate access to lineage information and associated sequences, but their classifications are maintained and revised rather than constituting final authorities. NCBI explicitly directs users to the relevant scientific literature for authoritative nomenclatural and taxonomic information. (ncbi.nlm.nih.gov)