The purpose of classification

A species is a group of organisms that are able to breed to produce fertile living offspring. Classification organises organisms into groups based on similarities.

This allows scientists to:

• Identify new species.
• Study evolutionary relationships.
• Understand shared traits and adaptations.
• Share research globally to identify links with organisms on other continents.

This hierarchical system from general to specific makes research and identification more manageable across the millions of global species.

The hierarchical taxonomic system

There are eight major taxonomic ranks used to classify organisms.

Ranked from largest and broadest to smallest and most specific, these are:

1. Domain
2. Kingdom
3. Phylum
4. Class
5. Order
6. Family
7. Genus
8. Species

The broadest groups contain the most species, and narrower groups have fewer species but are more closely related.

The domains

There are three domains that organisms can be classified into:

1. Bacteria
2. Archaea
3. Eukarya

While the domains Bacteria and Archaea both consist of prokaryotic organisms, the domain Eukarya includes all eukaryotes.

So, Eukarya includes four different kingdoms:

1. Plantae (plants)
2. Animalia (animals)
3. Protoctista (unicellular eukaryotes)
4. Fungi (such as yeasts)

Using binomial nomenclature

The binomial naming system gives each species a two-part ‘binomial’ Latin name. This binomial name is italicised when typed and underlined when written down.

The name consists of:

1. The genus - This has an uppercase first letter.
2. The species - This is all lowercase.

For example:

• The binomial name for humans is Homo sapiens.
• The binomial name for dogs is Canis familiaris.

This avoids confusion from regional common names for organisms.