What is taxonomy?

The understanding of relationships between living things is built upon the foundation of taxonomy.  The taxonomic hierarchy provides us with a way to classify living organisms and group those with similar characteristics together.  This system of categorization, that we still use today in a modified form, was developed by Carl Linnaeus in the 18th century and consists of seven ranks ranging from Kingdom to Species.399px-Biological_classification_L_Pengo_vflip.svg

Although other scientists used various classification systems prior to Linnaeus, they were varied and inconsistent.  In Historia Animalium, Aristotle attempted to divide animals by criteria such as those that belong to aquatic vs. terrestrial habitats.  However, Aristotle’s proposed system did not link organisms with genetic relationships.  Aristotle also did not consider the evolution of species, believing that they were static – an idea also accepted by naturalist John Ray.  This contradicts the evolutionary process of speciation by which organisms split into two or more species as they develop their own unique characteristics.  There are various types of speciation, but they all result in the production of new distinct species.

Later scientists of various backgrounds, including those such as Theophrastus, Cesalpino, and Bauhin, developed their own systems of categorization.  However, these systems only applied to certain groups of organisms.  Linnaeus was the first to use both hierarchal classification and binomial nomenclature together to create a more universal structure that applies to all organisms which is now consistently used throughout the scientific community.

Domains and Kingdoms

In 1990, Carl Woese added an eighth rank called domain to further categorize organisms by their genetic similarities.  This consists of three groups:

  1. Archaea
  2. Bacteria
  3. Eukarya

Prokaryotes (simplistic) and eukaryotes (complex) are the two basic types of cells.  Although at one point archaea and bacteria were grouped together as they are both prokaryotes, archaea share certain properties with both bacteria and eukarya that distinguish them enough to constitute a separate domain.  These domains consist of 6 kingdoms (also established by Woese) which include:

  1. Plants
  2. Animals
  3. Protists
  4. Fungi
  5. Archaebacteria
  6. Eubacteria

Remaining Ranks

The remaining ranks consist of far more numerous groups than the kingdoms and phyla, so I will not post the exhaustive list of them here.  However, I will show a few relevant animal classifications that should give you a better idea of how the system works.  As my previous post focused specifically on useful livestock terminology, I’ll use examples of major domesticated livestock and poultry species to demonstrate the taxonomic hierarchy.

Examples:

CattlePigSheepChicken
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Eukarya
Animalia
Chordata
Mammalia
Artiodactyla
Bovidae
Bos
Bos taurus
Eukarya
Animalia
Chordata
Mammalia
Artiodactyla
Suidae
Sus
Sus domesticus
Eukarya
Animalia
Chordata
Mammalia
Artiodactyla
Bovidae
Ovis
Ovis aries
Eukarya
Animalia
Chordata
Aves
Galliformes
Phasianidae
Gallus
Gallus gallus

The name of a species is always preceded by its genus, and following the first use the genus is usually abbreviated.   For example, Bos taurus would be written as B. taurus after the full name is first introduced in text. You will also notice that the first letter of the species is not capitalized, and both the genus and species should be italicized.  If writing by hand, the genus and species is underlined in place of italics.

You are probably already aware of various organisms’ taxonomic classifications such as E. coli (Escherichia coli) and Salmonella.  Salmonella is commonly referred to only by its genus due to both species being prevalent foodborne pathogens that can cause Salmonellosis.

As you can see, taxonomy is an important tool in classifying living organisms.  Whether we are speaking about other mammals or even bacteria, this system greatly simplifies the way in which we think about organisms and how they are connected.