In biology, binomial nomenclature is the formal method of naming species. As the word "binomial" suggests, the scientific name of a species is formed by the combination of two terms: the genus name and the species descriptor. Although the fine detail will differ, there are certain aspects which are universally adopted:
- Scientific names are usually printed in italics, such as Homo sapiens. When handwritten they should be underlined.
- The first term (genus name / generic name) is always capitalized, while the specific descriptor (in zoology, the "specific name", in botany, the "specific epithet") never is, even when derived from a proper name.
- For example, Canis lupus or Anthus hodgsoni. Note that this is a modern convention: Carolus Linnaeus always capitalized the specific descriptor, and up to the early 20th century it was common to capitalize the specific descriptor if it was based on a proper name. Although not correct according to modern practices, a capitalized specific descriptor is sometimes still used in non-scientific literature based on older sources.
- In scholarly texts, the main entry for the binomial is followed by the abbreviated (botany) or full (zoology) surname of the scientist who first published the classification. If the species was assigned to a different genus in the description than it is today, the abbreviation or name of the describer and the description date is set in parentheses.
- For example: Amaranthus retroflexus L. or Passer domesticus (Linnaeus, 1758) - the latter was originally described as member of the genus Fringilla, hence the parentheses.
- When used with a common name, the scientific name usually follows in parentheses.
- For example, "The house sparrow (Passer domesticus) is decreasing in Europe."
- The scientific name should generally be written in full when it is first used or when several species from the same genus are being listed or discussed in the same paper or report. It may then be abbreviated by just using an initial (and period) for the genus; for example Canis lupus becomes C. lupus. In rare cases this abbreviation form has spread to more general use — for example the bacterium Escherichia coli is often referred to as just E. coli, and Tyrannosaurus rex is perhaps even better known simply as T. rex.
- The abbreviation "sp." (zoology) or "spec." (botany) is used when the actual specific name cannot or need not be specified. The abbreviation "spp." (plural) indicates "several species".
- For example: "Canis sp.", meaning "one species of the genus Canis".
- Easily confused with the former is the abbreviation "ssp." (zoology) or "subsp." (botany) indicates an unspecified subspecies (see also trinomen, ternary name). "sspp." or "subspp." indicates "a number of subspecies".
- The abbreviation "cf." is used when the identification is not confirmed.
- For example Corvus cf. splendens indicates "a bird similar to the House Crow but not certainly identified as this species".
- Mycology uses the same system as in botany.
- Binomial nomenclature is also referred to as the 'Binomial Classification System'.
The adoption of a system of binomial nomenclature is due to Swedish botanist and physician Carolus Linnaeus (1707–1778) who attempted to describe the entire known natural world and gave every species (mineral, vegetable or animal) a two-part name. However, binomial nomenclature in various forms existed before Linnaeus, and was used by the Bauhins, who lived nearly two hundred years before Linnaeus. Before Linnaeus, hardly anybody used binomial nomenclature. After Linnaeus, almost everybody did.
Value of binomial nomenclature
The value of the binomial nomenclature system derives primarily from its economy, its widespread use, and the stability of names it generally favors:
- Every species can be unambiguously identified with just two words.
- The same name can be used all over the world, in all languages, avoiding difficulties of translation.
- Although such stability as exists is far from absolute, the procedures associated with establishing binomial nomenclature tend to favor stability. For example, when species are transferred between genera (as not uncommonly happens as a result of new knowledge), if possible the species descriptor is kept the same. Similarly if what were previously thought to be distinct species are demoted from species to a lower rank, former species names may be retained as infraspecific descriptors.
Despite the rules favoring stability and uniqueness, in practice a single species may have several scientific names in circulation, depending largely on taxonomic point of view (see synonymy).
Codes of nomenclature
From the mid nineteenth century onwards it became ever more apparent that a body of rules was necessary to govern scientific names. In the course of time these became Nomenclature Codes governing the naming of animals (ICZN), plants (incl. Fungi, cyanobacteria) (ICBN), bacteria (ICNB) and viruses. These Codes differ.
- For example, the ICBN, the plant Code does not allow tautonyms, whereas the ICZN, the animal Code does allow tautonymy.
- The starting points, the time from which these Codes are in effect (retroactively), vary from group to group. In botany the starting point will often be in 1753 (the year Carolus Linnaeus first published Species Plantarum), in zoology in 1758. Bacteriology started anew, with a starting point in 1980).
A BioCode has been suggested to replace several codes, although implementation is not in sight. There also is debate concerning development of a PhyloCode to name clades of phylogenetic trees, rather than taxa. Proponents of the PhyloCode use the name "Linnaean Codes" for the joint existing Codes and "Linnaean taxonomy" for the scientific classification that uses these existing Codes.
Derivation of names
The genus name and species descriptor may come from any source whatsoever. Often they are Latin words, but they may also come from Ancient Greek, from a place, from a person (preferably a naturalist), a name from a local language, etc. In fact, taxonomists come up with specific descriptors from a variety of sources, including inside-jokes and puns.
However, names are always treated grammatically as if they were a Latin sentence. For this reason the name of a species is sometimes called its "Latin name," although this terminology is frowned upon by biologists (and philologists), who prefer the phrase scientific name.
There is a separate list of Latin and Greek words commonly used in systematic names.
The genus name must be unique inside each kingdom. Species names are commonly reused, and are usually an adjectival modifier to the genus name, which is a noun. Family names are often derived from a common genus within the family.
- Curiosities of Biological Nomenclature
- The Language of Horticulture
- Principles of Nomenclature of Zoological Taxa
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