Taxonomy & Systematics

Introduction

Let us examine how this system works. The word taxonomy comprises two Greek words, taxis meaning arrangement and nomia meaning method. It is the classification of living beings into taxa (singular: taxon) which are groups of organisms that share similar characteristics, origins etc. These taxa or groups are then given different ranks. The various positions or levels can be grouped to form a higher class with more inclusive parameters. This is how taxonomical hierarchy is created. So, taxonomical hierarchy is the system in biology that classifies living beings.

The current system of taxonomic hierarchy was developed by Carl Linnaeus, an 18th-century Swedish botanist. He invented the binomial nomenclature, a method wherein an organism is given a two-part name made up of a genus and a species. Linnaeus published his work Systema Naturae, which detailed the binomial nomenclature and other aspects of the taxonomic hierarchy.

Taxonomist

A taxonomist is a scientist who makes natural groups of organisms by studying the various common factors and analysing shared characteristics. 

Taxonomical hierarchy 

Each rank in the taxonomic hierarchy becomes progressively more specific as one goes down the order. That is to say; the topmost rank is the most general or inclusive, containing several organisms from the various taxa or groups below it. And each successive rank becomes more specific, having fewer organisms until the last group or species, which includes a very particular population of animals or plants. 

The ranks in the taxonomic hierarchy in descending order are as follows:

1. Domain

 This rank is the most general of all ranks. It consists of three categories: bacteria, archaea and Eukaryota. The bacteria and archaea are single celled organisms differing from each other in the composition of their cellular structure. Eukarya consists of all the organisms, not in the different two categories.

This is a relatively new rank and was initially not given by Linnaeus.

Every rank is always written with a capital letter. This is to avoid confusion like bacteria the organism and Bacteria the domain.

2. Kingdom

 When Linnaeus introduced the taxonomic hierarchy, he started the classification with the rank of the kingdom. It consisted of Animalia, Plantae, Fungi, Protista, Bacteria and Archaea ( in some places, Bacteria and Archaea were combined to form the kingdom Monera). But today, some researchers have dinner with this rank altogether. This is because some of the groups are not very precise. For example, the kingdom Protista contains all eukaryotes other than plants, animals or fungi. But a lot of these leftover eukaryotes are not closely related.

3. Phylum

This is the rank after kingdom and before class. This is a more specific set of groupings, but being so high up in the classification order, there is still some disagreement regarding what makes up this class. Some researchers say that phylum Animalia is 35 in number. Others insist that Animalia consists of 31 species, Plantae has 14 and Fungi has 8. However, what is agreed upon is that Chordata ( all organisms with a spinal cord or dorsal nerve), Porifera (sponges) and Arthropoda (arthropods) are phylum in Animalia.

4. Class

There are 108 different classes in the kingdom Animalia. Some examples are Mammalia (mammals), Aves (birds) and Reptilia (reptiles). The courses of Animalia we use today are similar to those proposed by Linnaeus. However, he categorised plants according to such categories as flower arrangements rather than their degree of relatedness. So today, classes of plants are different from Linnaeus’ and are not used much in botany.

5. Order

This is a more specific category than class. Moreover, some orders put forth by Linnaeus are still in use today. Mammalia consists of 19 to 26 charges, but this depends on how the organisms are classified. Some orders of Mammalia are Primates (the great apes), Cetaceans (whales, dolphins, porpoises), Carnivora ( large carnivores) and Chiroptera (bats) etc.

6. Family

 This ranks congress between order and genus. Taxonomists decide what characteristics make up a family though there are no hard and fast rules for determining these characteristics. But plants can be divided into families depending on vegetation and reproduction. Even so, there is not much consensus regarding these divisions. Some suffixes are used while making families. These include the suffix -aceae for families in the taxonomic hierarchy of plants. And the suffix -idea for the family names of animals.

7. Genus

The genus is the second to last rank in the hierarchical taxonomic system. It is the first name in the binomial nomenclature and is always written with a capital letter should the species name be registered with all lower case letters. 

Taxonomists determine how the genus of organisms is determined and the classification practices may differ in different places. However, three broad criteria must be met to be classified as a genius, they are-

• Monophyly: Put, for organisms to be grouped in a particular genus, they must have a common ancestry.
• Reasonably compact: A genus should not be expanded to include too many organisms.
• Distinctness: The ecological, morphological and biogeographical criteria should be considered from an evolutionary point of view and should show distinct characteristics. 

8. Species

 This is the second part of binomial nomenclature and is the most basic unit in the taxonomic hierarchy of plants and animals. The most common way to determine a species is to determine if two members of the population can reproduce, mainly sexually and make fertile offspring. Other ways may include:-

•  DNA sequencing
• Determining the karyotype ( metaphase chromosomes sorted according to length, location of centromere, etc.) 
•  Morphology
•  Behaviour
•  Ecological niche

Binomial nomenclature

In the hierarchical taxonomic classification system, all species are given a two-part name. The first part is the name of the genus. The second part is the specific name or the specific epithet in the taxonomic hierarchy of plants. For example, Boa constrictor is one species out of four in the genus Boa. 

Examples of taxonomy 

• Domain: Eukaryota, Kingdom: Animalia ,Phylum: Chordata, Class: Mammalia, Order: Primates, Family: Hominidae, Genus: Homo, Species: sapiens.

Conclusion 

The hierarchical taxonomic system of classification is used in biology mainly for two purposes – identifying and making natural groups of organism populations. These are two very distinct purposes but are identified and used in combination in biology. This taxonomic hierarchy of plants and animals helps provide the most valuable characteristics for identifying an organism in a precise and brief way. That is why it is imperative to study these systems.