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Introduction to Biological Classification

Author(s): Deanne Erdmann, MS

Classification

Classification systems attempt to solve the problem of providing meaningful groupings of organisms. The Swedish scientist, Carolus von Linnaeus, is credited with introducing binomial nomenclature and hierarchical classification as an organized way of naming and describing organisms and their relationships to one another. Binomial nomenclature refers to the use of a two-part name for each species (one name designating genus and one designating species).

Linnaeus described a hierarchical classification system using seven taxonomic categories, or taxa (Kingdom, Phylum, Class, Order, Family, Genus, Species). Beginning with species, each category becomes progressively more comprehensive. For example, while the leopard, tiger and domestic cat all belong to different genera, they are grouped together in the same family.

Taxonomy is the science of classification. When taxonomic systems include hypothesized evolutionary relationships among groups, the field generally is referred to as Phylogenetics. Systematics is a larger field involving classifying organisms based on their phylogenetic relationships.  Systematics can be thought of as the study of biological diversity and how that diversity evolved. In a sense, Charles Darwin introduced systematics in his revolutionary work, The Origin of Species. He wrote, "The natural system is founded on descent with modification; that the characters which naturalists consider as showing true affinity between any two or more species, are those which have been inherited from a common parent, and, in so far, all true classification is genealogical" (Darwin, 1859).