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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.

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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.

Practice Example

Let’s take a look at the levels of classification and binomial nomenclature in action. You can see how the taxonomic levels are nested within each other:

Levels of classification and binomial nomenclature
diagram of different taxonomic levels

The lowest level taxon is the species. A species name consists of the genus name and the specific epithet.

All the taxonomic levels are shown for three species: a ladybug, you, and a dinosaur. These three species all belong to the same domain and the same kingdom. Humans and the dinosaur belong to the same phylum, but the ladybug belongs to a different one.

From this you can infer that humans are more closely related to this dinosaur than they are to the ladybug.

Lesson Summary

The binomial nomenclature system combines two names into one to give all species unique scientific names. The first part of a scientific name is called the genus. The second part of a species name is the specific epithet. Species are also organized into higher levels of classification. Each level of classification is called a taxon.

The highest and broadest taxon is called a domain. It is followed by kingdom, phylum, class, order, family, genus, and species.

Learning Outcomes

After you’ve completed this lesson, you should have the ability to:

  • Identify the purpose of binomial nomenclature
  • Explain the parts of a scientific name
  • Describe the scientific classification system

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