In biological classification, rank is the relative level of a group of organisms (a taxon) in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, class, kingdom, etc.
A given rank subsumes under it less general categories, that is, more specific descriptions of life forms. Above it, each rank is classified within more general categories of organisms and groups of organisms related to each other through inheritance of traits or features from common ancestors. The rank of any ''species'' and the description of its ''genus'' is ''basic''; which means that to identify a particular organism, it is usually not necessary to specify ranks other than these first two.〔(International Code of Nomenclature for algae, fungi, and plants, Melbourne Code, 2012, articles 2 and 3 )〕
Consider a particular species, the red fox ''Vulpes vulpes'': its next rank, the genus ''Vulpes'', comprises all the 'true foxes'. Their closest relatives are in the immediately higher rank, the family Canidae, which includes dogs, wolves, jackals, all foxes, and other caniforms; the next higher rank, the order Carnivora, includes feliforms and caniforms (lions, tigers, bears, hyenas, wolverines, and all those mentioned above), plus other carnivorous mammals. As one group of the class Mammalia, all of the above are classified among those with backbones in the Chordata phylum rank, and with them among all the animals in the Animalia kingdom rank. Finally, all of the above will find their earliest relatives somewhere in their domain rank Eukarya.
The ''International Code of Zoological Nomenclature'' defines rank as:
:The level, for nomenclatural purposes, of a taxon in a taxonomic hierarchy (e.g. all families are for nomenclatural purposes at the same rank, which lies between superfamily and subfamily)
== Main ranks ==
In his landmark publications, such as the ''Systema Naturae'', Carolus Linnaeus used a ranking scale limited to: kingdom, class, order, genus, species, and one rank below species. Today, nomenclature is regulated by the nomenclature codes. There are seven main taxonomic ranks: kingdom, phylum or division, class, order, family, genus, species. In addition, the ''domain'' (proposed by Carl Woese) is now widely used as one of the fundamental ranks, although it is not mentioned in any of the nomenclature codes.
A taxon is usually assigned a rank when it is given its formal name. The basic ranks are species and genus. When an organism is given a species name it is assigned to a genus, and the genus name is part of the species name.
The species name is also called a binomial, that is, a two-term name. For example, the zoological name for the human species is ''Homo sapiens''. This is usually italicized in print and underlined when italics are not available. In this case, ''Homo'' is the generic name and it is capitalized; ''sapiens'' indicates the species and it is not capitalized.
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