Taxonomy (biology)
Introduction
Taxonomy in biology is the branch of science concerned with classification, particularly of organisms. Systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic trees, phylogenies). Phylogenies have two components: branching order (showing group relationships) and branch length (showing amount of evolution). Phylogenetic trees of species and higher taxa are used to study the evolution of traits (e.g., anatomical or molecular characteristics) and the distribution of organisms (biogeography). Systematics, in other words, is used to understand the evolutionary history of life on Earth.
History
The concept of taxonomy has been in existence since the time of the ancient Greeks. The philosopher Aristotle is known to have classified animals based on their way of living, their behavior, and their physical attributes. This early attempt at classification was improved upon during the Middle Ages.
The modern system of taxonomy was developed by Carl Linnaeus, a Swedish botanist, physician, and zoologist, in the 18th century. Linnaeus introduced the concept of binomial nomenclature, a system of naming organisms that uses the Latin names of the genus and species. This system is still in use today and forms the basis of modern taxonomy.
Principles of Taxonomy
Taxonomy is based on three fundamental principles: the principle of priority, the principle of typification, and the principle of binomial nomenclature.
The principle of priority states that the first validly published name of a taxon (the plural is taxa, a group of one or more populations of an organism or organisms) takes precedence over names published later. If two names are found to be identical, the oldest published name is given priority.
The principle of typification involves the selection of a type specimen, which serves as a reference point for the species. The type specimen could be any specimen that shows the characteristic features of the species.
The principle of binomial nomenclature, introduced by Linnaeus, involves the use of two names, the genus name and the species name, to identify an organism. The genus name is always capitalized, while the species name is not. Both names are italicized.
Levels of Taxonomic Hierarchy
Taxonomy involves the hierarchical arrangement of organisms into a framework of classification. This hierarchy, from the broadest to the narrowest, includes: Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species. Each level in this hierarchy is referred to as a taxonomic rank.
Domain
The domain is the highest taxonomic rank. Currently, there are three recognized domains: Bacteria, Archaea, and Eukarya.
Kingdom
The kingdom is the second highest taxonomic rank. There are five kingdoms recognized today: Monera, Protista, Fungi, Plantae, and Animalia.
Phylum
The phylum is the rank below kingdom. Each kingdom is divided into multiple phyla. For example, the kingdom Animalia includes phyla such as Chordata, Arthropoda, and Mollusca.
Class
Each phylum is further divided into classes. For instance, the phylum Chordata includes classes like Mammalia, Aves, and Reptilia.
Order
Each class is divided into orders. For example, the class Mammalia includes orders such as Primates, Carnivora, and Rodentia.
Family
Each order is divided into families. For instance, the order Primates includes families like Hominidae, Cercopithecidae, and Tarsiidae.
Genus
Each family is divided into genera. For example, the family Hominidae includes genera such as Homo, Pan, and Gorilla.
Species
Each genus is divided into species. For instance, the genus Homo includes species like Homo sapiens, Homo neanderthalensis, and Homo erectus.
Modern Taxonomy
Modern taxonomy incorporates elements of many different sciences, including genetics, biochemistry, and paleontology, to name a few. The advent of DNA sequencing and genomic analysis has revolutionized the field, allowing for more precise classifications and a better understanding of the relationships between different organisms.
Taxonomists today use a variety of methods to classify organisms, including morphological, biochemical, and genetic characteristics. Morphological characteristics include physical attributes such as size, shape, and structure. Biochemical characteristics involve the analysis of the chemical compounds found in an organism, such as proteins, lipids, and nucleic acids. Genetic characteristics involve the analysis of an organism's DNA sequence.
Challenges in Taxonomy
Despite its long history and the advancements made in the field, taxonomy still faces several challenges. One of the major challenges is the sheer number of organisms that exist on Earth. It is estimated that there are between 10 million and 100 million species on Earth, but only about 1.2 million have been formally described and named.
Another challenge is the subjectivity involved in defining a species. Different taxonomists may have different interpretations of what constitutes a species, leading to disagreements and inconsistencies in classification.