The binomial system classifies organisms into groups at various hierarchic levels, on the basis of easily observable and shared morphological features like shape, number and position of limbs etc. in a descending order of group size. As the word binomial suggests, the name of a species is made up of two parts: one indicating the genus and indicating the species. Binomial nomenclature means “two part name” or “system of two part names”.
The person who popularized this system for use was Swedish Botanist and physician Carlous Linnaeus (1707-1778) who tried to name all things in the natural world and gave every species that he knew a two-part name. This kind of naming had been used before Linnaeus about everybody did.
In modern usage, the first letter of the first part of the name, the genus, is always capitalized in writing, while that of the second part is not, even when derived from a proper noun such as the name of a person or place similarly both parts are italicized when a binomial name occurs in normal text thus the binomial name of the human is Homo sapiens in zoology.
- “Patella vulgata Linnaeus, 1758”. The name “Linnaeus” tells the reader who it was that first published a description and name for this species of sea snail; 1758 is the date of the publication in which the original description can be found (in this case the 10th edition of the book Systema Naturae).
- “Passer domisticus (Linnaeus, 1758)” The original name given by Linnaeus was Tringilla domestica; the parentheses indicated that the species is now considered to belong 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 nomenclature catalogs usually include such information.
The value of binomial system of nomenclature derives primarily from its economy, its widespread use, and the uniqueness and stability of names it generally favours: Economy: compared to the polynomial system which it replaced, a binomial name is shorter and easier to remember. It corresponds to the widespread system of family name plus given name 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 and Tyrannosaurus rex.
Clarity : Binomial names avoid the confusion that can be created when attempting to use common names to refer to a species. Common names often differ from one country to another or even from one part of a country to another. In English-speaking North America, a “robin” is Turdus migratorius. In English speaking parts of Europe, the “robin” is Erithacus rubecula. In contrast, the scientific name can be used all over the world, in all languages, avoiding confusion and difficulties of translation.
Uniquenes : 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 accidently assigned to a species. However, establishing that two names actually refer to the same species and then determining which has priority can be difficult, particularly if the species was named by biologist from different countries. Therefore a species may have more than one regularly used name; these names are synonyms.
Stability : Although stability is far from absolute, the procedures associated with establishing binomial names, such as the principle of priority, tend to favour stability. Similarly, if what were previously thought to be two distinct species are demoted to a lower rank, such as subspecies, where possible the second part of the binomial name is as 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 Erithacus superbus or as only a subspecies, in which case its name is Erithacus rubecula superbus.
The superbus element of the name it constant since taxonomist can legitimacy disagree as to whether two genera or two species are distinct or not, more than one name can be in use. The only reason a specific epithet may need to be changed is if that by transferring it to a new genus it becomes a junier homonym of an older specific epithet for an older specific epithet for a different species in the same genus
Binomial system of nomenclature for species has the effect that when a species is moved from one genus to another not only is its genus name changed but sometimes its species name must be changed as well (because the name is already used in the new genus, or to agree in gender with the new genus) some biologist have argued for the combination of the genus name and specific epithet into a single unambiguous name, or for the use of uninominal (as used in nomenclature of ranks above species).
Relationship to classification and taxonomy
Nomenclature (including binomial system of nomenclature) is not the same as classification, although the two are related. Classification is the ordering of items into groups based on similarities and/or differences; in biological classification species are one of the binds of item to be classified. 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 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.
Taxonomy includes both nomenclature and classification. Its first stage (sometimes called alpha taxonomy) is concerned with finding, describing and naming species of living or fossil organisms. Binomial nomenclature is thus an important part of taxonomy as it is the system by which species are named. Taxonomists are also concerned with classification, including its principles, procedures and rules
Derivation of binomial names
A complete binomial name is always treated grammatically as if it were a phase in the Latin language (hence the common use of the term “Latin name” for a binomial name). however, the two parts of a binomial name can each be derived from a number of source, of which Latin is only one. These include :
- Latin, either classical or medieval thus both parts of the binomial name Homo sapiens are Latin words, meaning “wise” (sapiens), human/man (Homo).
- Classical Greek the genus Rhododendron was named by Linnaeus from the Greek word which is itself derived from rhodos, rose and Dendron tree. Greek words are often converted to a Latinized form. Thus coca (the plant from which cocaine is obtained) has the name Erythroxylun coca. Erythroxylun is derived from the Greek words erythros, red and xylon, wood. The Greek neuter ending –ov(-on) is often converted to the Latin neuter ending –um.
Other language: The second part of the name Erythroxylun coca is derived from kuka, the name of the plant is Aymara and Quenchua. Since many dinosaur fossils were found in Mongolia, their names often use Mongolian words e.g. Tarchia from turki, meaning “brain” or Saichania meaning “beautiful one”. Name of people (often naturalist or biologists): the name Magnolia campbellii commemorates two people; Pierre Magnol , a French botanist, and Archibald Campbell, a doctor in British India.
Name of the place : The lone star tick, Amolyomna americanum, is wide spread in the United States.
Other sources : Some binomial names have been constructed from anagrams or other re-ordering of existing names. Thus the name of the Muilla is derived by reversing the name Allium. Name may also be derived from jokes or puns. For example, Ratcliffe described a number of species of Rhinoceros bettle, including Cyclocephala nodanotheruon. The first part of the name, which identifies the genus, must be a word which can be created as a Latin singular noun in the nominative case it must be unique within each kingdom, but can be repeated between kingdoms. Thus Huia recurvata is an extinct species of plant, found in fossils in Yunnan, China, whereas Huia masonii is a speciesof frog found in Java, Indonesia.
The second part of a binomial may be an adjective. The adjective must agree with the genus in gender. Latin has three genders, masculine, feminine and neuter, shown by varying endings to nouns and adjectives. The house sparrow has the binomial name Passer domesticus. Here domesticus (Domestic) simply means “associated with the house” the sacred bamboo is Nandina domestica rather than Nandina domesticus, since tropical fruit langsat is a product of the plant Lansium parasiticum since lansium is neuter. Some common endings for Latin adjectives in these genders (masculine, feminine, neuter) are –us, -a, -um (as in the previous example of domesticus); -is, -e (e.g. tristis meaning sad), and –or, -us (e.g. minor, meaning smaller).
The second part of a binomial may be a noun in the nominative case. An example is the binomial name of the lion, which is Panthera leo grammatically the noun is said to be in opposition to to the genus name and the two nouns do not have to agree in gender, in this case, Panthera is feminine and Leo is masculine.
The second part of a binomial may be a noun in the genitive (possessive) case. The genitive case is constructed in a number of ways in Latin, depending on the declension of the noun. Common endings for masculine and neuter nouns are – ii or –I in the singular and –orum in the plural and for feminine nouns –ae in the singular and –arum in plural.
The noun may be part of a person’s name, often the surrounding as in the Tibetan antelope, Pantholops hodgsonii, the shrub Magonolia hodgsonii or the olive backed pipit Anthus hodgsonii. The meaning is “of the person named” so that magnolia hodgsonii means “Hodgson’s magnolia”. The –ii or –i endings show that in each case Hodgson was a man (not the same one); the person commemorated in the binomial name is not usually (if ever) the person who created the name; for example Anthus hodgson.
Rather than person the noun may be related to a place, as with Latimera chaulmnae, meaning “of the Chaulmna River”. Another use of genitive noun is in, for example, the name of the bacterium Escherichia coli, where coli mean “of the colon”. This formation is common in parasites as in Xenos vesparum, where vesparum means “of the wasps” since Xenos vesparum is a parasite of wasps. Whereas the first part of a binomial name must be unique within a kingdom, the second part is quite commonly used in two or more genera (as is shown by examples of hodgsonii above).
The full binomial name must be unique within a kingdom.
Writing binomial names
By tradition, the binomial names of species are usually typeset in italics; for example, Homo sapiens. Generally the binomial should be printed in a font different from that used in the normal text; for example “several more Homo sapiens fossils were discovered”. When hand written, each part of a binomial name should be underlined; for example Homo sapiens. The first part of the binomial, the genus name, is always written with an initial capital letter. In current usage, the second part is never written with an initial capital.
The binomial name should generally be written in full. The exception to this is when several species from the same genus are being listed or discussed in the same paper or report, or the same species is mentioned repeatedly; in which case the genus is written in full when it is first used, but may then be abbreviated to an initial (and a period/full stop) for example, a list of members of the genus can might be written as “Canis lupus, C. aureus, C. simensis”.
In rare cases, this abbreviated form has spread to more general use; for example, the bacterium, Escherichia coli is often referred to as first E. coli and Tyrannosaurus rex is T. rex these two both often appearing in this form in popular writing even where the full genus name has not already been given.
The abbreviation “spp.” (Plural) indicates “several species”. These abbreviations are not italicized (or underlined) for example “Canis sp.” Means an unspecified species of the genus Canis, while “Canis spp.” Means “two or more species of the genus Canis” (The abbreviations sp.” and spp.” Can easily be confused with the abbreviations “ssp.” (Zoology) or “subsp.” (Botany), plurals “sspp.” or “subspp” referring to one or more subspecies.
The abbreviation “cf” (i.e. confer in latin) is used to compare individuals/taxa with known/described species conventions for use of the “cf” qualifier vary. In paleontology, it is typically used when the identification is not confirmed. For example “corvus cf nasicus” was used to indicate “a fossil bird similar to the Cuban crow but not certainly identified as this species”. In molecular systematic papers, “cf” may be used to indicate one or more undescribed species assumed related to a described species.
For example, in a paper describing the phylogeny of small benthic fresh water fish called darters, five undescribed putative species (Ozark, Sheltowea, Wildcat, Ihiyo and Mamequit darters), notable for brightly coloured nuptial males with distinctive color patterns, were referred to as “Etheostoma cf spectabile” because they had been viewed as related to, but with distinct form, Etheostoma spectbile (orange throat darter). This view was supposed in varying degree by DNA analysis.
The somewhat informed use of taxa names with qualifying abbreviations is referred to as open nomenclature and it is not subject to strict usage wells. In some context the dagger (“f”) may be used before or after the binomial name to indicate that the species is extinct.