Taxonomy

circa 1760: Swedish physician and botanist Carl von Linnaeus (1707-1778), founder of the modern system of binomial nomenclature for plants. Original Publication: From a copy by Pasch of an original painting. Hulton Archive / Stringer/ Hulton Archive/ Getty Images

Taxonomy is a hierarchical system for classifying and identifying organisms. This system was developed by Swedish scientist Carolus Linnaeus in the 18th century.

Binomial Nomenclature

Linnaeus's taxonomy system has two main features that contribute to its ease of use in naming and grouping organisms. The first is the use of binomial nomenclature. This means that an organism's scientific name is comprised of a combination of two terms.

These terms are the genus name and the species or epithet. Both of these terms are italicized and the genus name is also capitalized.

For example, the scientific name for humans is Homo sapiens. The genus name is Homo and the species is sapiens. These terms are unique and no other species can have this same name.

Classification Categories

The second feature of Linnaeus's taxonomy system that simplifies organism classification is the ordering of species into broad categories. The major categories include: Kingdom, Phylum, Class, Order, Family, Genus, and Species. These categories have been updated to include Domain in the taxonomic hierarchy. Domain is the broadest category and organisms are grouped primarily according to differences in ribosomal RNA structure.

A good aid for remembering taxonomic categories is the mnemonic device: DKeep Plates Clean Or Family Gets Sick.

Taxonomic categories can be further divided into intermediate categories such as subphyla, suborders, superfamilies, and superclasses.

An example of this taxonomy scheme is below. It includes the eight main categories along with subcategories and supercategories. The superkingdom rank is the same as the Domain rank.

Taxonomic Hierarchy
 Category  Subcategory  Supercategory 
   
Domain   
Kingdom SubkingdomSuperkingdom (Domain)
PhylumSubphylumSuperphylum
ClassSubclassSuperclass
OrderSuborderSuperorder
FamilySubfamilySuperfamily
GenusSubgenus 
SpeciesSubspeciesSuperspecies

The table below includes a list of organisms and their classification in this taxonomy system using the major categories. Notice how closely dogs and wolves are related. They are similar in every aspect except species name.

Taxonomic Classification
  Brown BearHouse CatDogKiller WhaleWolf

Tarantula  Spider

DomainEukaryaEukaryaEukaryaEukaryaEukaryaEukarya
KingdomAnimaliaAnimaliaAnimaliaAnimaliaAnimaliaAnimalia
PhylumChordataChordataChordataChordataChordataArthropoda
ClassMammaliaMammaliaMammaliaMammaliaMammaliaArachnida
OrderCarnivoraCarnivoraCarnivoraCetaceaCarnivoraAraneae
FamilyUrsidaeFelidaeCanidaeDelphinidaeCanidaeTheraphosidae
GenusUrsusFelisCanisOrcinusCanisTheraphosa
SpeciesUrsus arctosFelis catusCanis familiarisOrcinus orcaCanis lupusTheraphosa blondi