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The International Code of Zoological Nomenclature (ICZN) is both a book containing (among others) a set of rules and recommendations on the formal naming of animals, and that set itself. Among zoologists (and in the book) it is often referred to simply as "the Code" (in mixed company, taxonomists refer to it as "the ICZN"). It was first published in 1961, although it has precedents going back to 1842; the present edition is the fourth edition (1999). The Code is issued by the International Commission on Zoological Nomenclature. As the Commission may alter the Code without issuing a new edition of the book, it is not necessarily so that the book contains the actual provision that applies in a particular case.

The Code deals with zoological nomenclature, which is defined in the Glossary as

"The system of scientific names for animal taxa and the provisions for the formation, treatment, and use of those names."

Zoological nomenclature is independent of other systems of nomenclature.

The rules and recommendations have one fundamental aim: to provide the maximum universality and continuity in the naming of all animals, except where taxonomic judgment dictates otherwise. The Code is meant to guide only the nomenclature of animals, while leaving the zoologists freedom in classifying new taxa. In other words, whether a species itself is or is not an entity to be recognized is a subjective decision, but what name should be applied to it is not; the Code applies only to the latter, not to the former. A new animal name published without adherence to the Code may be deemed simply "unavailable" if it fails to meet certain criteria, or fall entirely out of the province of science (e.g., the "scientific name" for the Loch Ness Monster).

The rules in the Code determine what names are valid for any taxon in the family group, genus group, and species group. It has additional (but more limited) provisions on names in higher ranks. The Code recognizes no case law. Any dispute is to be decided first by applying the Code directly, and not by reference to precedent.



In regulating the names of animals it holds by six central principles, which were first set out (as Principles) in the third edition of the Code (1985):


The Code divides names in the following manner:

  • Names above the family group.
  • Family-group names.
  • Genus-group names.
  • Species-group names.

The names above the family group are regulated only as to the requirements for publication; there is no restriction to the number of ranks and the use of names is not restricted by priority.

The names in the family group, the genus group and the species group are fully regulated by the provisions in the Code. There is no limitation to the number of ranks allowed in the family group. In the genus group there are only two ranks: the genus and the subgenus. In the species group there are only two ranks: the species and the subspecies.


Gender agreement

In the species group gender agreement applies. The name of a species, in two parts, a binomen, say, Loxodonta africana, and of a subspecies, in three parts, a trinomen, say Canis lupus albus, originally is a Latin phrase, and must be grammatically correct Latin. If the second part, the specific name (or the third part, the subspecific name) is adjectival in nature, its ending must agree in gender with the name of the genus. If it is a noun, or an arbitrary combinations of letters, this does not apply.

  • For instance, the generic name Equus is masculine; in the name Equus africanus the specific name africanus is an adjective and its ending follows the gender of the generic name.
  • In Equus zebra the specific name zebra is a noun, it may not be "corrected" to "Equus zebrus".
  • In Equus quagga burchellii the subspecific name burchellii is a noun in the genitive ("of the esteemed Burchell").

If a species is moved, therefore, the spelling of an ending may need to be changed. Confusion over proper Latin grammar have led to many incorrectly-formed names appearing in print. An improper automated search may fail to find all the variant spellings of a given name (e.g., the spellings atra and ater may refer to the same species). Accordingly, many laymen and some scientists object to continued adherence to this long-standing rule.


The rules in the Code are to be followed by all users of zoological names. However, its provisions can be interpreted, waived or modified in their application to a particular case when strict adherence would cause confusion. Such exceptions are not made by an individual scientist, no matter how well-respected within his or her field, but only by the International Commission on Zoological Nomenclature, acting on behalf of all zoologists. The Commission takes such action in response to proposals submitted to it.

  • Carolus Linnaeus named the Domestic Cat Felis catus in 1758; Johann Christian Daniel von Schreber named the Wildcat Felis silvestris in 1775. For taxonomists who consider these two kinds of cat to be a single species the Principle of Priority means that the species ought to be named F. catus, but in practice almost all biologists have used F. silvestris. In 2003, the Commission issued a ruling (Opinion 2027) that "conserved the usage of 17 specific names based on wild species, which are pre-dated by or contemporary with those based on domestic forms", confirming F. silvestris for the wild cat. Taxonomists who consider the domesticated cat to be the same species as the wild cat should use F. silvestris; taxonomists who consider the domesticated cat a subspecies of the wild cat should use F. silvestris catus; taxonomists who consider the domesticated cat a separate species should use F. catus.[1]

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