The system for scientifically naming organisms, known as binomial nomenclature, provides a universally recognized and unambiguous label for every species. Established by Carl Linnaeus in the 18th century, this two-part naming system uses Latin or Latinized words to ensure global consistency. The scientific name consists of the genus and the species epithet, following specific formatting rules dictated by international codes of nomenclature. Understanding the precise application of capitalization is fundamental to correctly using this standardized biological language.
The Core Capitalization Rule
The fundamental rule of binomial nomenclature dictates that the two parts of a species name are treated differently regarding capitalization. The first word, representing the genus, must always begin with a capital letter because it is considered a proper noun.
In contrast, the second part of the name, the specific epithet, is always written entirely in lowercase letters. This rule holds true even when the epithet is derived from a proper noun, such as a person’s name or a geographic location. For instance, the scientific name for the gray wolf is Canis lupus, where the genus Canis is capitalized, but the specific epithet lupus is not.
After the scientific name has been introduced in full, it is standard practice to abbreviate the genus to its capitalized first initial. In subsequent mentions, Homo sapiens becomes H. sapiens, and Felis catus would be abbreviated to F. catus. The capitalization of the genus initial remains mandatory, provided that the abbreviation does not create confusion with another genus mentioned in the same text that shares the same initial.
The Role of Italicization
While capitalization distinguishes the two parts of the name, italicization visually isolates the scientific name from the surrounding text. Both the capitalized genus and the lowercase species epithet must be italicized in print or typed documents. This formatting convention signals to the reader that the words are being used as a formal scientific designation.
The need for italicization stems from the Latin grammatical form of the name, which is treated as a foreign phrase within English text. Therefore, the complete binomial, such as Quercus alba for the white oak, must be rendered in italics. If the text were being handwritten, the entire scientific name would be underlined instead of italicized.
This rule applies consistently across all domains of life. Even when the genus name is abbreviated to a single letter, the initial and the species epithet remain italicized, as seen in E. coli for Escherichia coli. The combined use of capitalization and italicization is the complete formatting standard for a species’ scientific name.
Naming Higher Taxonomic Ranks
Taxonomic ranks above the genus level, such as Family, Order, Class, Phylum, and Kingdom, follow a distinct capitalization rule. These higher taxa are always capitalized, reflecting their status as proper nouns that designate major classification groups. For example, the family that includes cats is Felidae, the order is Carnivora, and the class is Mammalia.
These higher taxonomic ranks are generally not italicized in scientific writing. The lack of italics distinguishes them from the two-part species name, which requires both capitalization and italicization.
When a higher rank is referenced in its adjectival or common form, it loses its capitalization. For instance, while the Family name is capitalized as Hominidae, an organism belonging to that family is often referred to simply as a “hominid,” which is written in lowercase. This distinction helps to maintain clarity in biological discourse.
Distinguishing Scientific and Common Names
The capitalization rules for scientific names differ significantly from the conventions used for common names. Common names, which are the local, everyday terms for organisms, typically adhere to standard English grammar rules. They are only capitalized if they appear at the beginning of a sentence or if they contain a proper noun.
For example, the common name “grizzly bear” is usually written in lowercase unless it starts a sentence. If a common name incorporates a person’s name or a geographical place, only that proper noun element is capitalized, as seen in names like “Swainson’s hawk” or “African elephant.”
A major source of inconsistency arises because different scientific disciplines, such as ornithology, have adopted conventions that capitalize all elements of a common name to reduce ambiguity. In these specific fields, the name for a bird like the American Robin is capitalized as a proper name. Despite these exceptions, the non-capitalization of the species epithet in the formal scientific name, like Turdus migratorius for the American robin, remains an unwavering rule.