Classification

Classification, in biology, systematic arrangement of the world's organisms into categories based on their characteristics. This science, sometimes called taxonomy, is often aimed at establishing evolutionary relationships. The system of classification comprises 7 major categories. These are, from most to least inclusive: kingdom; phylum (called division in botany); class; order; family; genus; species. Traditionally, there were only 2 kingdoms, plants and animals. Today, however, most biologists would recognize 3 others: the Protista (1-celled organisms and some forms of algae), the Monera (bacteria and blue-green algae), and the Fungi (mushrooms and molds). The species is the basic unit of classification. As a rule of thumb, 2 animals belong to the same species if they are capable of mating to produce fertile offspring.

See also: Biology.