In taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages. Such a name is called a binomial name (often shortened to just "binomial"), a binomen, name, or a scientific name; more informally, it is also called a Latin name. In the International Code of Zoological Nomenclature (ICZN), the system is also called nomenclature, with an "n" before the "al" in "binominal", which is a typographic error, meaning "two-name naming system".
The first part of the name – the generic name – identifies the genus to which the species belongs, whereas the second part – the specific name or specific epithet – distinguishes the species within the genus. For example, modern humans belong to the genus Homo and within this genus to the species Homo sapiens. The formal introduction of this system of naming species is credited to Carl Linnaeus, effectively beginning with his work Species Plantarum in 1753. But as early as 1622, Gaspard Bauhin introduced in his book (English, Illustrated Exposition of Plants) containing many names of genera that were later adopted by Linnaeus. Binomial nomenclature was introduced in order to provide succinct, relatively stable and verifiable names that could be used and understood internationally, unlike common names which are usually different in every language.
The application of binomial nomenclature is now governed by various internationally agreed codes of rules, of which the two most important are the International Code of Zoological Nomenclature (ICZN) for animals and the International Code of Nomenclature for algae, fungi, and plants (ICNafp or ICN). Although the general principles underlying binomial nomenclature are common to these two codes, there are some differences in the terminology they use and their particular rules.
In modern usage, the first letter of the generic name is always capitalized in writing, while that of the specific epithet is not, even when derived from a proper noun such as the name of a person or place. Similarly, both parts are italicized in normal text (or underlined in handwriting). Thus the binomial name of the annual phlox (named after botanist Thomas Drummond) is now written as . Often, after a species name is introduced in a text, the generic name is abbreviated to the first letter in subsequent mentions (e.g., ).
In scientific works, the authority for a binomial name is usually given, at least when it is first mentioned, and the year of publication may also be specified. In zoology " Linnaeus, 1753". The name "Linnaeus" tells the reader who published the name, and description for this species; 1753 is the year the name and original description were published (in this case, in the 10th edition of the book Systema Naturae). " (Linnaeus, 1758)". The original name given by Linnaeus was ; the parentheses indicate that the species is now placed in a different genus. The ICZN does not require that the name of the person who changed the genus be given, nor the date on which the change was made, although nomenclatorial catalogs usually include such information. In botany " L." – "L." is the standard abbreviation used for "Linnaeus". " (L.) Rothm." – Linnaeus first named this bluebell species ; Rothmaler transferred it to the genus ; the ICNafp does not require that the dates of either publication be specified.
Etymology The word binomial is composed of two elements: (Latin prefix meaning 'two') and (the adjective form of , Latin for 'name'). In Medieval Latin, the related word was used to signify one term in a binomial expression in mathematics. In fact, the Latin word may validly refer to either of the epithets in the binomial name, which can equally be referred to as a (pl. ).
History
Before the adoption of the modern binomial system of naming species, a scientific name consisted of a generic name combined with a specific name that was from one to several words long. Together they formed a system of polynomial nomenclature. These names had two separate functions: to designate or label the species, and to be a diagnosis or description. These two goals were eventually found to be incompatible. In a simple genus that contained few species, it was easy to tell them apart with a one-word genus and a one-word specific name; but as more species were discovered, the names necessarily became longer and unwieldy—for instance, ("plantain with pubescent ovate-lanceolate leaves, a cylindric spike and a terete scape"), which we know today as Plantago media.
Such "polynomial names" may sometimes look like binomials, but are different. For example, Gerard's herbal (as amended by Johnson) describes various kinds of spiderwort: "The first is called , Branched Spiderwort; the second, , Unbranched Spiderwort. The other ... is aptly termed , Soon-Fading Spiderwort of Virginia". The Latin phrases are short descriptions, rather than identifying labels.
The Bauhins, in particular Caspar Bauhin (1560–1624), took some important steps towards the binomial system by pruning the Latin descriptions, in many cases to two words., p. v The adoption by biologists of a system of strictly binomial nomenclature is due to Swedish botanist and physician Carl Linnaeus (1707–1778). It was in his 1753 Species Plantarum that Linnaeus began consistently using a one-word trivial name () after a generic name (genus name) in a system of binomial nomenclature. Trivial names had already appeared in his Critica Botanica (1737) and Philosophia Botanica (1751). This trivial name is what is now known as a specific epithet (ICNafp) or specific name (ICZN). The Bauhins' genus names were retained in many of these, but the descriptive part was reduced to a single word.
Linnaeus's trivial names introduced the idea that the function of a name could simply be to give a species a unique label, meaning that the name no longer needed to be descriptive. Both parts could, for example, be derived from the names of people. Thus Gerard's became Tradescantia virginiana, where the genus name honoured John Tradescant the Younger, an English botanist and gardener. A bird in the parrot family was named Psittacus alexandri, meaning "Alexander's parrot", after Alexander the Great, whose armies introduced eastern parakeets to Greece. Linnaeus's trivial names were much easier to remember and use than the parallel polynomial names, and eventually replaced them.
Nowadays, many species are mainly referred to by their binomial names, even in non-specialized fields, such as environmental education and the internet in general. Because of this use, the binomial Tyrannosaurus rex is widely known.
Value
The value of the binomial nomenclature system derives primarily from its economy, its widespread use, and the uniqueness and stability of names that the Codes of Zoological and Botanical, Bacterial and Viral Nomenclature provide: Economy. Compared to the polynomial system which it replaced, a binomial name is shorter and easier to remember. It corresponds to the noun-adjective form many vernacular names take to indicate a species within a group (for example, 'brown bear' to refer to a particular type of bear), as well as the widespread system of family name plus given name(s) used to name people in many cultures. Widespread use. The binomial system of nomenclature is governed by international codes and is used by biologists worldwide. A few binomials have also entered common speech, such as Homo sapiens, E. coli, Boa constrictor, Tyrannosaurus rex, and Aloe vera. Uniqueness. Provided that taxonomists agree as to the limits of a species, it can have only one name that is correct under the appropriate nomenclature code, generally the earliest published if two or more names are accidentally assigned to a species. This means the species a binomial name refers to can be clearly identified, as compared to the common names of species which are usually different in every language. However, establishing that two names actually refer to the same species and then determining which has priority can sometimes be difficult, particularly if the species was named by biologists from different countries. Therefore, a species may have more than one regularly used name; all but one of these names are "synonyms". Furthermore, within zoology or botany, each species name applies to only one species. If a name is used more than once, it is called a homonym.
Stability. Although stability is far from absolute, the procedures associated with establishing binomial names, such as the principle of priority, tend to favor stability. For example, when species are transferred between genera (as not uncommonly happens as a result of new knowledge), the second part of the binomial is kept the same (unless it becomes a homonym). Thus, there is disagreement among botanists as to whether the genera Chionodoxa and Scilla are sufficiently different for them to be kept separate. Those who keep them separate give the plant commonly grown in gardens in Europe the name Chionodoxa siehei; those who do not give it the name . The siehei element is constant. Similarly, if what were previously thought to be two distinct species are demoted to a lower rank, such as subspecies, the second part of the binomial name is retained as a trinomen (the third part of the new name). Thus, the Tenerife robin may be treated as a different species from the European robin, in which case its name is , or as only a subspecies, in which case its name is . The superbus element of the name is constant, as are its authorship and year of publication.
Problems Binomial nomenclature for species has the effect that when a species is moved from one genus to another, sometimes the specific name or epithet must be changed as well. This may happen because the specific name is already used in the new genus, or to agree in gender with the new genus if the specific epithet is an adjective modifying the genus name. Some biologists have argued for the combination of the genus name and specific epithet into a single unambiguous name, or for the use of uninomials (as used in nomenclature of ranks above species).
Because genus names are unique only within a nomenclature code, it is possible for homonyms (two or more species sharing the same genus name) to happen, and even the same binomial if they occur in different kingdoms. At least 1,258 instances of genus name duplication occur (mainly between zoology and botany).
Relationship to classification and taxonomy Nomenclature (including binomial nomenclature) is not the same as classification, although the two are related. Classification is the ordering of items into groups based on similarities or differences; in biological classification, species are one of the kinds of item to be classified., p. 552 In principle, the names given to species could be completely independent of their classification. This is not the case for binomial names, since the first part of a binomial is the name of the genus into which the species is placed. Above the rank of genus, binomial nomenclature and classification are partly independent; for example, a species retains its binomial name if it is moved from one family to another or from one order to another, unless it better fits a different genus in the same or different family, or it is split from its old genus and placed in a newly created genus. The independence is only partial since the names of families and other higher taxa are usually based on genera.