What is Taxonomy?


Taxonomy is the method used to naming, defining (circumscribing) and classifying groups of biological organisms based on shared characteristics such as morphological characteristics, phylogenetic characteristics, DNA data, etc. It is founded on the concept that the similarities descend from a common evolutionary ancestor.

Defined groups of organisms are known as taxa. Taxa are given a taxonomic rank and are aggregated into super groups of higher rank to create a taxonomic hierarchy. The taxonomic hierarchy includes eight levels: Domain, Kingdom, Phylum, Class, Order, Family, Genus and Species.

Example of taxonomy. It starts, top to bottom, with Kingdom "Animalia", Phylum "Chordata", Class "Mammalia", and Order "Carnivora". Then it splits in 3. On the left, Family "Felidae", with 2 genus "Felis" and "Panthera" and below 3 species "F. catus" and "F. pardalis" below "Felis", "P. pardus" below "Panthera". In the middle, Family "Canidae", genus "Canis" and 2 species "C. familiaris" and "C. lupus". On the right, Family "Ursidae", Genus "Ursus" and 2 species "U. arctos" and "U. horribilus". Below each species is a illustration of the species

The classification system begins with 3 domains that encompass all living and extinct forms of life

  • The Bacteria and Archae are mostly microscopic, but quite widespread.
  • Domain Eukarya contains more complex organisms

When new species are found, they are assigned into taxa in the taxonomic hierarchy. For example for the cat:

Level Classification
Domain Eukaryota
Kingdom Animalia
Phylum Chordata
Class Mammalia
Order Carnivora
Family Felidae
Genus Felis
Species F. catus

From this classification, one can generate a tree of life, also known as a phylogenetic tree. It is a rooted tree that describes the relationship of all life on earth. At the root sits the “last universal common ancestor” and the three main branches (in taxonomy also called domains) are bacteria, archaea and eukaryotes. Most important for this is the idea that all life on earth is derived from a common ancestor and therefore when comparing two species, you will -sooner or later- find a common ancestor for all of them.

Let’s explore taxonomy in the Tree of Life, using Lifemap

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