Which of the following taxonomic ranks is least inclusive?

Levels of Taxonomy Used in Biology

De Agostini Picture Library / Getty Images

Taxonomy is the practice of categorizing and naming of species. The official "scientific name" of an organism consists of its Genus and its Species Identifier in a naming system called binomial nomenclature.

The Work of Carolus Linnaeus

The current taxonomic system gets its roots from the work of Carolus Linnaeus in the early 1700s. Before Linnaeus set up the rules of the two-word naming system, species had long and unwieldy Latin polynomials that were inconsistent and inconvenient for scientists when communicating with each other or even the public.

While Linnaeus's original system had many fewer levels than the modern system has today, it was still an excellent place to start to organize all of life into similar categories for easier classification. He used the structure and function of body parts, mostly, to classify the organisms. Thanks to advances in technology and understanding the evolutionary relationships among species, we have been able to update the practice to get the most accurate classification system possible.

The Taxonomic Classification System

The modern taxonomic classification system has eight main levels (from most inclusive to most exclusive): Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species Identifier. Every different species has a unique species identifier and the more closely a species is related to it on the evolutionary tree of life, it will be included in a more inclusive group with the species being classified.

(Note: An easier way to remember the order of these levels is to use a mnemonic device to remember the first letter of each word in order. The one we use is "Do Keep Pond Clean Or Fish Get Sick")

Domain

A domain is the most inclusive of the levels (meaning it has the most number of individuals in the group). Domains are used to distinguish between the cell types and, in the case of prokaryotes, where they are found and what the cell walls are made of. The current system recognizes three domains: Bacteria, Archaea, and Eukarya.

Kingdom

Domains are further broken into Kingdoms. The current system recognizes six Kingdoms: Eubacteria, Archaebacteria, Plantae, Animalia, Fungi, and Protista.

Phylum

The next division would be the phylum.

Class

Several related classes make up a phylum.

Order

Classes are further divided into Orders.

Family

The next level of classification that orders are divided into are Families.

Genus

A genus is a group of closely related species. The genus name is the first part of the scientific name of an organism.

Species Identifier

Each species has a unique identifier that describes only that species. It is the second word in the two-word naming system of the scientific name of a species.