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Binomial Nomenclature: Definition, Classification & System

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  • 0:02 Binomial Nomenclature…
  • 1:47 Binomial Nomenclature Rules
  • 2:26 Higher Classification
  • 3:33 Practice Example
  • 4:16 Lesson Summary
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Lesson Transcript
Instructor: Angela Lynn Swafford

Lynn has a BS and MS in biology and has taught many college biology courses.

Life on Earth is incredibly diverse, with over one million species. But have you ever wondered how all these organisms are named? In this lesson, you'll learn about the scientific naming system called binomial nomenclature.

Binomial Nomenclature Definition

The most well-known living things have common names. For example, you are probably familiar with the small, red insects dotted with little black spots. You might call them 'ladybugs' or 'ladybird beetles.' But did you know there are actually many different species of these insects? Just using common names may make it difficult for scientists to differentiate between them, so every species is given a unique scientific name.

Binomial nomenclature is the formal naming system for living things that all scientists use. It gives every species a two-part scientific name. For example, a ladybug found in the United States goes by the fancy name of Harmonia axyridis.

The first part of a scientific name, like Harmonia, is called the genus. A genus is typically the name for a small group of closely related organisms. The second part of a scientific name, axyridis in this example, is the specific epithet. It is used to identify a particular species as separate from others belonging to the same genus. Together, the genus plus the specific epithet is the full scientific name for an organism.

I bet that you actually already know the scientific name for at least one animal, although you may not have realized it. Ever heard of the dinosaur T. rex? T. rex is actually a scientific name - the 'T' is just an abbreviation of the genus Tyrannosaurus. So the scientific name is actually Tyrannosaurus rex.

Binomial Nomenclature Rules

Because scientific names are unique species identifiers, they ensure that there is never any confusion as to which organism a scientist may be referring. Additionally, there are some important rules that must be followed to keep all binomial names standardized:

  1. The entire two-part name must be written in italics (or underlined when handwritten).
  2. The genus name is always written first.
  3. The genus name must be capitalized.
  4. The specific epithet is never capitalized.

Higher Classification

In addition to giving a species a binomial scientific name, it must also belong to higher levels of classification. Each level of classification is called a taxon (plural is taxa). The broadest taxon is the domain. All living things fit into only three domains: archaea, bacteria, and eukarya. Nested within each of these domains, there are kingdoms. Each kingdom contains phyla (singular is phylum). The taxonomic levels below phylum are class, order, family, genus, and species.

That might seem like a lot to take in, but you can always use a mnemonic device. Try this one on for size: 'Dear King Philip Came Over For Good Soup.' This can help you remember the order of the taxonomic levels from largest to smallest: domain, kingdom, phylum, class, order, family, genus, and species.

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