Short answer
A genus is the broader rank; a species is the narrower rank nested within it. In a two-part scientific name, the first word is the genus and the second is the specific epithet; together they identify the species. A genus can include several species. 1 2
A species belongs to a genus in the conventional taxonomic hierarchy.
On this page
At a glance
Scroll to compare all columns →
| Question | Species | Genus |
|---|---|---|
| Rank | Narrower | Broader |
| Scientific name | Genus plus specific epithet | First word of a binomial |
| Can contain | Organisms classified together | One or more species |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Species. A taxonomic rank below genus, used for a named group of organisms. 1
Genus. A taxonomic rank above species, grouping one or more related species. 1
Key differences
The specific epithet alone is not the complete species name. Taxonomists use the paired name because the same epithet can appear in different genera. Genus and species are ranks in a classification scheme informed by evolutionary relationships, not measurements of organism size or importance. 1 2
How to tell them apart
Look at a scientific binomial: in Homo sapiens, Homo is the genus and Homo sapiens is the species name. Do not call “sapiens” the species by itself when precision matters. If two organisms share a genus name but differ in the second word, they are classified as different species within that genus. 1 2
Where they overlap
Both are nested classification categories and both can change when evidence changes the grouping of organisms. A species name explicitly contains its genus name. 1 2
Edge cases
Species boundaries can be difficult for fossils, asexually reproducing organisms and closely related populations. Genus limits can also be revised; the rank describes a classification decision rather than a perfectly fixed natural container. 1 2
Why the distinction exists
Hierarchical naming provides a compact way to identify organisms and express grouping. The broader genus and narrower species let names remain informative across related forms. 1 2
Common misconceptions
A genus is not another word for a single species. Nor is the second word of a binomial a stand-alone universal species label. 1 2
Examples
Homo sapiens and another named Homo species share the genus Homo while remaining different species under that classification. 1 2
Sources
Sources checked October 3, 2026.
- OpenStax Biology 2e — Organizing Life on Earth. Classification Levels.
- OpenStax Biology 2e — Understanding Evolution. Species and population change.