Taxonomy (Biology): Definition, Classification & Examples

Taxonomy in biology is the process of placing organisms into similar groups based on certain criteria. Natural scientists use a taxonomy key to identify plants, animals, snakes, fish and minerals by their scientific names.

For example, a house cat is Felis catus: a genus and species name assigned in 1758 by Swedish botanist Carolus Linnaeus, the “father of taxonomy.”

Naming of Taxonomic Groups

International researchers use scientific names to understand the shared characteristics and evolutionary history of living organisms. Determining that a peculiar new species is a bird is just a starting point for taxonomists. The American Museum of Natural History estimates that there are approximately 18,000 species of birds with unique traits that complicate identification, for example.

Taxonomic classification uses a system of binomial nomenclature like Homo sapiens; the word for the genus is capitalized, and both words are italicized, even when writing about a single species or just the genus alone.

Taxonomy (Biology): Definition

Taxonomy is the science of describing, naming, and classifying organisms with increasing specificity. Latin names are used in a worldwide system of classification that goes from broad to specific categories. Scientists need a uniform system of naming in order to have meaningful conversations about new and uncommon types of animals, plants, protists and other organisms.

Every organism is identified by a two-word scientific name (the aforementioned genus and species). For example, there are many different types of pines within the generic group of Pinus (this is the genus). Specific types of pines, such as the commonly known Ponderosa pine, go by the scientific name of Pinus ponderosa (the second word is the name for the species). When the genus name has already been mentioned in a written source, the genus is often abbreviated to an initial, as in P. ponderosa.

Taxonomy actually includes an entire hierarchy of successively narrower categories, with the genus and species at the narrower, more detailed end. Domains are the largest and broadest category.

Scientists commonly use the Three Domain System to depict the evolutionary history of living things based on the idea that all cells share a least universal common ancestor (LUCA) that evolved into three umbrella domains: the prokaryotic Archaea, prokaryotic Bacteria and eukaryotic Eukarya. Domains are divided further into kingdom, phylum, class, order, family, genus and species.

Note that only genus and species names are italicized:

  • Domain: Eukarya.
  • Kingdom: Animalia.
  • Phylum: Chordata.
  • Class: Mammalia.
  • Order: Primates.
  • Family: Homindae_._
  • Genus: Homo.
  • Species: H. sapiens (modern human).

Importance of Taxonomy in Biology

Identifying taxonomic groups shows how living things relate to one another. Scientists use behavior, genetics, embryology, comparative anatomy and fossil records to classify a group of organisms with shared characteristics. A universal nomenclature system facilitates communication between researchers conducting similar studies.

In the western world, Aristotle and his protégé, Theophrastus, are credited with being the first scholars to use a taxonomy to make sense of the natural world. Aristotle’s classification system grouped animals with comparable features into genera (this is the plural of genus), similar to the current division of vertebrates and invertebrates.

Advances in Taxonomy

According to the Linnean Society of London, Carolus (Carl) Linnaeus is known as the “father of taxonomy” and is considered a pioneer in the field of ecology. Linnaeus authored the well-known Systema Naturae, the first edition of which was published in 1735. Linnaeus established the uniform naming hierarchy still used today with that two-word system of binomial nomenclature.

The Linnaean (also written as Linnean) system divided life into two kingdoms: Animalia and Vegetabilia, largely based on morphology.

Charles Darwin’s famous work On the Origin of Species expanded the 18th-century Linnaean classification system to include phyla (singular: phylum) and evolutionary relationships. French zoologist Jean-Baptiste Lamarck made the distinction between vertebrates and invertebrates.

German scientist Ernst Haeckel (also sometimes spelled as Haeckl) introduced a tree of life with three kingdoms: Animalia, Plantae and Protista.

In the 1940s, Ernst Mayr, an ornithologist and curator at the American Museum of Natural History, made a groundbreaking discovery in evolutionary biology. Mayr observed that isolated populations evolve differently as the result of random mutations and natural selection. Eventually, the differences give rise to a new species. His findings shed new light on the process of speciation and taxonomic classification.

How Does a Taxonomy Key Work?

Taxonomists are like detectives; they make careful observations and ask many questions to solve a mystery. A taxonomy key is a tool that presents a series of dichotomous taxonomy questions in biology that require a "yes" or "no" answer. Through the process of elimination, the key leads to identification of the specimen. There are different types of keys, and taxonomists do not always agree on classification schema.

For example:

  1. Does it have more than eight legs? If yes, go to next question. If no, go to question 5.
  2. Does it have jointed antennae? If yes, go to next question. If no, go to question 6.
  3. Does it have a segmented body? If yes, go to next question. If no, go to question 7.
  4. Does it have one pair of flattened legs on most segments? If yes, it is a centipede. If no, it is a millipede.
  5. Does it have six legs? If yes, go to next question. If no, go to question 9.

Taxonomy (Biology): Naming New Species

When scientists come across unfamiliar organisms, several strategies are used to make a positive identification. Research, genetic testing, taxonomy keys and dissection can help narrow down the possibilities.

If no match is found, the specimen may represent a new discovery. At that point, scientists write a description, sort it into a taxonomic group and assign a scientific name using the standard Latin naming system format.

Cladograms and Evolutionary Classification

Modern taxonomy considers the physical traits of an organism when making identification, but greater emphasis is placed on evolutionary history. A tree-like diagram known as a cladogram is used to show how species hypothetically branched out during evolution and acquired traits called derived characteristics. Derived characters are innovative traits that evolved more recently in the lineage.

For example, teeth and claws that appear later in the lineage that were not present in ancestors are considered derived characteristics.

Life continually adapts and evolves. Beneficial traits improve chances of survival and are more likely to be passed along to offspring. Evolutionary relationships are determined by comparing similarities and differences in living things that share a common ancestor. A cladogram could be used to illustrate how turtles, snakes, birds and dinosaurs fit within the class of Reptilia, for instance.

What Is a Phylogenetic Tree?

The phylogenetic tree is a classification system that arranges organisms by evolutionary relationships. The tree of life has several branches that spring from a common ancestor.

Each node on the tree represents divergence into different species. Two species are closely related if they share a recent common ancestor at a point of divergence.

Taxonomy (Biology) Examples

Taxonomic classification reveals fascinating ties between different organisms. For instance, birds are closely related to crocodiles and dinosaurs, according to the phylogenetic system of classification. Birds evolved from feathered dinosaurs that did not go extinct millions of years ago.

Birds belong to the reptilian diapsid group, and crocodiles evolved from archosaurs, a subset of diapsids.

Frontiers in Classification

Advances in technology have improved the accuracy of taxonomy when classifying living organisms. Analysis of DNA and RNA in cells can reveal unsuspected similarities between different species.

For instance, vultures and storks share similar genes that denote a common ancestor. Based on DNA evidence, the Smithsonian National Museum of Natural History indicates that modern humans and chimpanzees shared a common ancestor 6-8 million years ago.

New technology comes at a critical time in the history of the Earth. According to the American Museum of Natural History, an extinction event may be looming.

For example, climate change may lead to the mass extinction of millions of species that have not even yet been named. Computer-aided classification helps taxonomists identify new species before they go extinct, allowing researchers to possibly save them.