The binomial naming system is an internationally accepted method of giving every species a two-part scientific name: the genus name followed by the specific epithet. For example, the scientific name for humans is Homo sapiens.
This content is required at both SL and HL in A3.1 Diversity of organisms.
How the System Works
“Binomial” means “two names.” The first word identifies the genus, a group containing closely related species. The second word distinguishes the species from other species in that genus.
For example, Pan troglodytes is the common chimpanzee, while Pan paniscus is the bonobo. Both belong to the genus Pan, but their different specific epithets identify them as different species.
Naming rule | Correct example |
|---|---|
The genus name begins with a capital letter | Homo |
The specific epithet begins with a lowercase letter | sapiens |
Both words are italicized when typed | Homo sapiens |
Both words are underlined separately when handwritten | Homo sapiens |
After the first full use, the genus may be abbreviated | H. sapiens |
Scientific names are usually derived from Latin or treated as Latin. This gives biologists a universal naming system and avoids confusion caused by different common names in different languages or regions.
A common misconception is that the second word alone is the species name. Strictly, the complete species name is the full binomial, such as Homo sapiens; sapiens alone is the specific epithet.
Exam Technique
For IB Biology, write binomial names with correct capitalization and formatting. In a state or identify question, give the full two-part name; when handwriting, underline each word separately. Do not capitalize the specific epithet or use only the common name when a scientific name is requested.
