Taxonomy is the practice of identifying different organisms, classifying them into categories, and naming them. All organisms, both living and extinct, are classified into distinct groups with other similar organisms and given a scientific name. The study of the names of organisms is called Nomenclature.
Taxonomy is a sub-discipline of Systematics which is the study of those relationships. The word taxonomy is also used in non-biological contexts to describe any system of classification. Nomenclature is a sub-discipline of taxonomy.
Scientists who study taxonomy are called taxonomists.
The Greek scientist, Aristotle, was one of the first scientists to organize living things. He developed the first classification system which divided all known organisms into two groups: Plants and Animals. Each of these main groups was then divided into three smaller subgroups.
Animal subgroups: Land, Water, Air
Plant subgroups: Small, Medium, Large
There were gaps in Aristotle’s classification system. There were so many organisms that didn’t fit. For example, frogs are born in water and have gills like fish, but when they grow up they have lungs and can live on land. So, how Aristotle’s classification system classifies frogs? In Aristotle’s classification system, birds, bats, and flying insects were grouped together even though have little in common except that they can fly. But penguin is a bird that cannot fly, so Aristotle could not have classified them as birds.
Even with the many problems, Aristotle’s classification system was used for nearly 2000 years until it was replaced in the 1700s by the Swedish biologist Carolus Linnaeus (1707-1778).
Like Aristotle, Linnaeus classified organisms according to their traits. He developed the taxonomic system, called binomial nomenclature that is used throughout biology. His original system was first published in 1735 under the title Systema Naturae – considered to be the ‘bible of taxonomy’. The system has evolved over time but remains essentially the same.
The classification systems of both Aristotle and Linnaeus started with the same two groups: Plants and Animals. Linnaeus called these groups ‘kingdoms’. But unlike Aristotle, Linnaeus divided the kingdom into five levels – class, order, genus, species and variety. Organisms were placed in these levels based on traits, including similarities of body parts, physical form such as size, shape, and methods of getting food.
In Systema Naturae, Linnaeus classified nature into a hierarchy. The classification of organisms has various hierarchical categories. Categories gradually shift from being very broad and including many different organisms to very specific and identifying single species.
He proposed that there were three broad groups called kingdoms into which the whole of nature could fit. These kingdoms were animals, plants and minerals. He divided each of these kingdoms into classes. Classes were divided into orders and orders were further divided into genus and then species. We still his system today but we have made some changes.
Today, we only use this system to classify living things. Linnaeus included non-living things in his mineral kingdom. Also, we have added a few additional levels in the hierarchy.
Each level of classification is also called a taxon (plural is taxa).
The broadest level of life is now a domain. A domain is a taxon that is larger and more inclusive than the kingdom. All living things fit into only three domains: Archaea, Bacteria, and Eukarya.
Within each of these domains, there are kingdoms. Both Bacteria and Archaea consist of single-celled prokaryotes. Eukarya consists of all eukaryotes, from single-celled protists to humans. This domain includes the Animalia (animals), Plantae (plants), Fungi (fungi), and Protista kingdoms. For example, Eukarya includes the kingdoms Animalia, Fungi, Plantae and more.
Each kingdom contains phyla (singular phylum). It is still a very broad classification but it splits kingdoms into multiple groups. Within the animal kingdom, major phyla include chordate (animals with a backbone or vertebrates), arthopoda (includes insects) and mollusca (mollusks such as snails). Invertebrates are separated into many different phyla.
Each phylum is then divided into classes. Classes within the chordate phylum include mammalia (mammals), reptilia (reptiles) and osteichthyes (fish), among others. Arthropod classes include the likes of insects and arachnids (spiders, mites, and scorpions).
The class is then subdivided into an order. Within the class mammalian, examples of order include cetacea (including whales and dolphins), carnivore (carnivores), primates (monkeys, apes, and humans) and chiroptera (bats).
From the order, the organism will be classified into a family. Within the order of primates, families include hominidae (great apes and humans), cercopithecidae (old world monkeys such as baboons0 and hylobatidae (gibbons and lesser apes).
The final two categories are genus and species. The genus and species that an organism belongs to are how an organism receives its scientific name. This naming system is called ‘binomial nomenclature’ invented by the biologist Carl Linnaeus.
One outstanding feature of the Linnaean Classification System is that two names are generally sufficient to differentiate from one organism to the next. An example within the primate family is the genus Homo for all human species (for example, Home sapiens) or Pongo for the genus if orangutan (for example Pongo abelii) for the Sumatran orangutan or Pongo pygmaeus for the Bornean orangutan.
An identified species are placed into a specific group in each of these categories. For example, the taxonomic classification of humans is
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Hominidae
Genus: Homo
Species: Homo sapiens
To remember the order of the taxonomic hierarchy from domain to species, people often use mnemonics to make it easier. One good phrase to remember the taxonomic hierarchy is Dear King Philip Came Over For Good Soup.
Binomial Nomenclature is the method that we use to uniquely name every different organism on Earth, living or extinct. All organisms have a scientific name that includes two Latin words. These two words are made from the names of the genus the species belongs to and a second word to separate each of the species within the same genus. Hence, the scientific names of all organisms are made from the name of their genus and a specific name.
For example, the scientific name given to humans includes their genus Homo and the specific name sapiens. The overall name is Homo sapiens.
When writing species names, it is important to remember the names are in Latin and need to be italicized or underlined. The Genus is always capitalized, and both the Genus and Species names should be underlined. For example, the scientific name for Short-tailed shrew is Blarina brevicauda. All other taxonomic classification such as Families, Orders, etc should be capitalized.
