classification



classification defined in 1951 year

classification - classification;
classification - Organisms are classified scientifically in a hierarchical series of groups. The smallest group regularly used is the species. Species which are more like each other than like other species are grouped together in a genus; similarly genera are grouped into families, families into orders, orders into classes, classes into phyla or divisions, and phyla or divisions into kingdoms, the highest taxonomic rank. Various sub-groups are also used as necessary. All groups of any one kind, e.g. all families, are supposed to have approximately the same 'weight', e.g. every family is supposed to differ from its related families belonging to the same order, by a roughly equal amount and the same degree of difference should be found in every order. Consequently a single peculiar family like that comprising genera of amphioxus cannot be put in an order along with any other family, and must form an order, and in this case a class and sub-phylum, by itself.

Usual form of classification, natural classification, is based on overall resemblances, as distinct from artificial classification based on one or few characters and used for special purposes, e.g. ease of identification. Since the more closely related by descent organisms are, the more features they have in common, natural system of classification may also reflect degrees of evolutionary relationship, i.e. it may also be pkylogenetic. The system generally accepted is not a rigid one. Biologists differ among themselves on many points of classification, and the system is always subject to modification as more and more is learnt about organisms, and about their fossil history. At present the criteria used for classifying organisms are almost entirely structural; but as we learn more of biochemical and physiological differences, other criteria will no doubt be used in constructing the classificatory system.

near classification in Knolik


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