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In biology, binomial nomenclature is a standard convention used
for naming species. As the word 'binomial' suggests, the scientific name of each species is the combination of two names: the
genus name and the species epithet. The name
of the genus (generic name) is always capitalized, while the specific epithet (trivial name) is not; both are usually typeset in
italics, e.g. Homo sapiens. The genus name is usually abbreviated to its initial letter when several species from the
same genus are being listed, or discussed in a single paragraph; in a few cases this abbreviation has spread to more general use
- for example the bacterium Escherichia coli is usually referred to as
E. coli.
Origin of names
The names used are usually derived from Latin. Although Latin derivation is not
universal (names sometimes come from Ancient Greek, sometimes from local
languages, often from the name of the person who first described a species) and sometimes in a playful way, such as a pun, the names are always treated grammatically as if they were Latin words. For this reason the
binomial name of a species is sometimes called its "Latin name", though this usage is frowned on by biologists. The term
"Scientific name" is more acceptable. There is a separate list of Latin and Greek words commonly used in systematic
names.
Value of the binomial system
The value of the binomial system derives primarily from its economy and its
widespread use:
- the same name is used in all languages, avoiding difficulties of translation;
- every species can be unambiguously identified with just two words;
- the system has been adopted internationally in botany (since 1753), zoology (since 1758) and bacteriology
(since 1980¹).
The procedures associated with establishing binomial nomenclature tend to favor stability. In particular, when species are
transferred between genera (as not uncommonly happens as a result of new knowledge), wherever possible species names are kept the
same. Similarly if what were previously thought to be distinct species are found to belong to a single species, former species
names are when applicable retained as a lower taxon name.
However, such stability as exists is far from being absolute. A single organism may have several scientific names in
circulation, depending on opinion (see synonymy), conservation according to nomenclature codes, and new
findings based on molecular phylogeny. Another source of
instability is the rule that nomenclature should respect priority of discovery.
Extending the binomial name
Trinomial nomenclature
When a species is further divided, a trinomial
nomenclature is used, e.g. Astrophytum myriostigma subvar. glabrum.
In botany, a species can be further
divided into any of subspecies, variety, subvariety or form, whereas in zoology, a species is only subdivided into subspecies.
Trinomial names of plants therefore usually include a qualifier (such as "subvar." in the example above), whereas
trinomial names of animals never do. For example, Phalacrocorax carbo novaehollandiae is the Black Shag, the subspecies
of the Great Cormorant found in Australia and New Zealand, and there
is no need to indicate explicitly that novaehollandiae is a subspecies name.
Authorship in scientific names
Sometimes you will see a name or abbreviation after a scientific name, sometimes including a date, generally at the top of a
page. An official reference to a species includes not only the genus and species, but the author(s) of the name. This is usually
abbreviated if possible, e.g. Urtica dioica L. where "L." refers to Linnaeus. While the name is
italicized, the author is not. If a species is moved into a different genus, the original author is put in parentheses and the
author who moved it is appended, e.g. Chamaecyparis nootkatensis (D. Don) Spach which was originally
described as Cupressus nootkatensis by D. Don. This has been recently moved to a new genus and has now
become Xanthocyparis nootkatensis (D. Don) Farjon & Hiep. This addition of authorship is usually
only done once in a particular article or citation. In articles where species are described or moved, the date is usually added
as well but this is rare in encyclopedic or other non-taxonomic articles.
Hierarchy
The binomial name of a species, of course, only reflects part of the larger classification of the organism:
Carolus Linnaeus invented this classification, but it is a common misconception
that he also invented binomial nomenclature; in fact it dates back to the Bauhins.
Linnaeus, however, was the first to systematize and popularize it, and it is only one aspect of his systematical achievements or
misachievements (such as oversimplifying fungal systematics).
Binomial nomenclature is only one of many conventions used to name organisms. Nomenclature codes rule the
naming of plants (incl. Fungi, cyanobacteria) / cultivated plants / animals / bacteria / viruses. These codes differ. For example, the ICBN plant nomenclature
does not allow tautonymy, whereas the ICZN
animal code allows it. A BioCode has been
suggested to replace several codes, but there also is debate of a PhyloCode to
name clades of phylogenetic
trees.
For more information on this system, please see scientific classification and numerical taxonomy.
Footnote
- The botanical code kept references to bacteria until 1975. A bacteriological code of nomenclature was approved at the 4th
International Congress for Microbiology in 1947, but was later discarded. The official "Nomenclatural Starting Date" for the
current International Code for bacteria is January 1, 1980.
See also
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