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classification, in biology, the systematic categorization of organisms into a coherent scheme. The original purpose of biological classification, or systematics, was to organize the vast number of known plants and animals into categories that could be named, remembered, and discussed. Modern classification also attempts to show the evolutionary relationships among organisms (see the table entitled Examples of Systematic Classification). A system based on categories that show such relationships is called a natural system of classification; one based on categories assigned only for convenience (e.g., a classification of flowers by color) is an artificial system.
Modern classification is part of the broader science of taxonomy, the study of the relationships of organisms, which includes collection, preservation, and study of specimens, and analysis of data provided by various areas of biological research. Nomenclature is the assigning of names to organisms and to the categories in which they are classified.
A modern branch of taxonomy, called numerical taxonomy, uses computers to compare very large numbers of traits without weighting any type of trait : in contrast to the traditional view that certain characteristics are more significant than others in showing relationships. For example, the structure of flower parts is considered more significant than the shape of the leaves in flowering plants because leaf shape appears to evolve much more quickly. Much of the science of taxonomy has been concerned with judging which traits are most significant. If new evidence reveals a better basis for subdividing a taxon than that previously used, the classification of the group in question may be revised. A considerable number of classification changes as well as insights in recent years have been the result of comparisons of nucleic acid (genetic material) sequences of organisms.
See also cladistics.
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