Taxonomy is the study and practice of classification. The method relies on categories that start broad and divide the group with further smaller groups, until a single object is in its own group. For example, a couch is a specific piece of furniture, while a leather couch is a specific couch, and so on. While this method can be applied to the classification of any subject, it is most famously regarded as the method of classification for the Earth’s life.
Carl Linnaeus created the original biological system, now called the Linnaean Taxonomy, around the mid to late 18th century. Due to the lack of knowledge about DNA and evolution, Linnaeus based his hierarchy on the structural similarities between creatures instead of genetic similarities. While the advent of evolutionary theory helped place many creatures in their correct branches, Linnaeus did a magnificent job creating a relatively accurate account of known species.
All organisms were divided by 7 mandatory ranks. From least to most specific, they are Kingdom, Phylum/Division (Phylum refers to animals, while Division refers to plants), Class, Order, Family, Genus, and Species. This order can be easily memorized by a simple mnemonic: “(K)ing (P)hilip (C)alled (O)ut (F)or (G)ood (S)oup.” Recently, a new rank was created, ranking above the kingdom, called the Domain. It changed the division of Kingdoms significantly.
Domains are the most modern addition to the taxonomy system. They are divided into three domains. Eukarya are creatures that have internal organelles with in their cells. Plants, Animals, Fungi, and some bacteria are contained within this domain. Eubacteria and Archea are prokaryotes. They do not have internal cell structures. The sole difference between the two domains is the divergence in cellular history. These Domains are further divided into Kingdoms.
Kingdoms are the highest ranking level or organisms. The old Five Kingdom version gave us divisions of Animalia (Animals), Plantae (Plants), Fungi, Protista(Bacteria), and Monera (Different Bacteria). Due to the lack of significant difference between Protista and Monera, the Domain system was favored over the Five Kingdom method.
Phylum, or Divisions in plants and some bacteria. This division outlines the most basic shared body feature of all that share it. For example, Phylum Mollusca contains animals with shell-secreting mantles and Division Angiosperma contains flowering plants. There are many phylum and there are too many to list.
Classes are a division of Phylum that can contain even more ranks, such as Class Mammalia, which contains the Mammal branch, and Class Reptilia, which holds reptiles. These classes, like many of the branches below it, are in flux. Certain scientist may decide that a certain class is no longer a good example, and may bump it up to a Phylum, or demote it to an Order. This is common when new knowledge comes to light, such when a new species is discovered, or a new fossil changes perceptions on an evolutionary branch.
Even the common hierarchical system with it’s multiple ranks, was ultimately not sufficiently detailed. As knowledge of the natural world progressed and the number of groups of organisms identified became larger and larger, it became necessary to create further subcategories. These include Tribe between Family and Genus; and Division and Cohort between Class and Order. Moreover, each category can also have prefixes to create a higher grouping (super-), or lower (sub-, infra-) divisions. For example, we get superorder, suborder, infraorder, subgenus, and subspecies. All of life is given a two word, Latin name according to their Genus and Species. A Linnaean Taxonomy for humans would be written accordingly:
Subphylum – Vertebrata
Order – Primates
Thus, the system produces the familiar name Homo Sapiens for humans and gives us a biological description of major features. For example, Chordata is the phylum heading for all creatures that have a notochord and a hollow dorsal nerve chord. Vertebrata is a subphylum, or a specification of Chordata, which tells us that humans have vertebra, or a backbone. By starting from the top rank, we eventually get a full description of the organism, from what type of cell it consists of, to what kind of environment it lives in.
This is a very basic form, and other species may need other categories to help differentiate one very similar organism from another. The system is versatile enough to allow additions to the list, while the major organization is rigid enough to allow for consistency in naming. Taxonomy is a complex study. It cannot be done justice in an essay. To fully understand the subtleties and intricacies taxonomy, further study must be done on one’s own.