verteWhereas Linnaeus aimed simply to create readily identifiable taxa, the idea of the Linnaean taxonomy as translating into a sort of dendrogram of the animal and plant kingdoms was formulated toward the end of the 18th century, well before On the Origin of Species was published.[25] Among early works exploring the idea of a transmutation of species were Erasmus Darwin's 1796 Zoönomia and Jean-Baptiste Lamarck's Philosophie Zoologique of 1809.[12] The idea was popularized in the Anglophone world by the speculative but widely read Vestiges of the Natural History of Creation, published anonymously by Robert Chambers in 1844.[40]
With Darwin's theory, a general acceptance quickly appeared that a classification should reflect the Darwinian principle of common descent.[41] Tree of life representations became popular in scientific works, with known fossil groups incorporated. One of the first modern groups tied to fossil ancestors was birds.[42] Using the then newly discovered fossils of Archaeopteryx and Hesperornis, Thomas Henry Huxley pronounced that they had evolved from dinosaurs, a group formally named by Richard Owen in 1842.[43][44] The resulting description, that of dinosaurs "giving rise to" or being "the ancestors of" birds, is the essential hallmark of evolutionary taxonomic thinking. As more and more fossil groups were found and recognized in the late 19th and early 20th centuries, palaeontologists worked to understand the history of animals through the ages by linking together known groups.[45] With the modern evolutionary synthesis of the early 1940s, an essentially modern understanding of the evolution of the major groups was in place. As evolutionary taxonomy is based on Linnaean taxonomic ranks, the two terms are largely interchangeable in modern use.[46]
The cladistic method has emerged since the 1960s.common descent.[41] Tree of life representations became popular in scientific works, with known fossil groups incorporated. One of the first modern groups tied to fossil ancestors was birds.[42] Using the then newly discovered fossils of Archaeopteryx and Hesperornis, Thomas Henry Huxley pronounced that they had evolved from dinosaurs, a group formally named by Richard Owen in 1842.[43][44] The resulting description, that of dinosaurs "giving rise to" or being "the ancestors of" birds, is the essential hallmark of evolutionary taxonomic thinking. As more and more fossil groups were found and recognized in the late 19th and early 20th centuries, palaeontologists worked to understand the history of animals through the ages by linking together known groups.[45] With the modern evolutionary synthesis of the early 1940s, an essentially modern understanding of the evolution of the major groups was in place. As evolutionary taxonomy is based on Linnaean taxonomic ranks, the two terms are largely interchangeable in modern use.[46]
The cladistic method has emerged since the 1960s.[41] In 1958, Julian Huxley used the term clade.[12] Later, in 1960, Cain and Harrison introduced the term cladistic.[12] The salient feature is arranging taxa in a hierarchical evolutionary tree, ignoring ranks.[41] A taxon is called monophyletic, if it includes all the descendants of an ancestral form.[47][48] Groups that have descendant groups removed from them are termed paraphyletic,[47] while groups representing more than one branch from the tree of life are called polyphyletic.[47][48] The International Code of Phylogenetic Nomenclature or PhyloCode is intended to regulate the formal naming of clades.[49][50] Linnaean ranks will be optional under the PhyloCode, which is intended to coexist with the current, rank-based codes.[50]
Well before Linnaeus, plants and animals were considered separate Kingdoms.[51] Linnaeus used this as the top rank, dividing the physical world into the plant, animal and mineral kingdoms. As advances in microscopy made classification of microorganisms possible, the number of kingdoms increased, five- and six-kingdom systems being the most common.
Domains are a relatively new grouping. First proposed in 1977, Carl Woese's three-domain system was not generally accepted until later.[52] One main characteristic of the three-domain method is the separation of Archaea and Bacteria, previously grouped into the single kingdom Bacteria (a kingdom also sometimes called Monera),[51] with the Eukaryota for all organisms whose cells contain a nucleus.[53] A small number of scientists include a sixth kingdom, Archaea, but do not accept the domain method.[51]
Thomas Cavalier-Smith, who has published extensively on the classification of Domains are a relatively new grouping. First proposed in 1977, Carl Woese's three-domain system was not generally accepted until later.[52] One main characteristic of the three-domain method is the separation of Archaea and Bacteria, previously grouped into the single kingdom Bacteria (a kingdom also sometimes called Monera),[51] with the Eukaryota for all organisms whose cells contain a nucleus.[53] A small number of scientists include a sixth kingdom, Archaea, but do not accept the domain method.[51]
Thomas Cavalier-Smith, who has published extensively on the classification of protists, has recently proposed that the Neomura, the clade that groups together the Archaea and Eucarya, would have evolved from Bacteria, more precisely from Actinobacteria. His 2004 classification treated the archaeobacteria as part of a subkingdom of the kingdom Bacteria, i.e., he rejected the three-domain system entirely.[54] Stefan Luketa in 2012 proposed a five "dominion" system, adding Prionobiota (acellular and without nucleic acid) and Virusobiota (acellular but with nucleic acid) to the traditional three domains.[55]
Partial classifications exist for many individual groups of organisms and are revised and replaced as new information becomes available; however, comprehensive, published treatments of most or all life are rarer; recent examples are that of Adl et al., 2012 and 2019,[63][64] which covers eukaryotes only with an emphasis on protists, and Ruggiero et al., 2015,[65] covering both eukaryotes and prokaryotes to the rank of Order, although both exclude fossil representatives.[65] A separate compilation (Ruggiero, 2014)[66] covers extant taxa to the rank of family. Other, database-driven treatments include the Encyclopedia of Life, the Global Biodiversity Information Facility, the NCBI taxonomy database, the Interim Register of Marine and Nonmarine Genera, the Open Tree of Life, and the Catalogue of Life. The Paleobiology Database is a resource for fossils.
Application
Biological taxonomy is a sub-discipline of biology, and is generally practiced by biologists known as "taxonomists", though enthusiastic naturalists are also frequently involved in the publication of new taxa.[67] Because taxonomy aims to describe and organize life, the work conducted by taxonomists is essential for the study of biodiversity and the resulting field of conservation biology.[68][69]
Classifying organisms
Biological classification is a critical component of the taxonomic process. As a result, it informs the user as to what the relatives of the taxon are hypothesized to be. Biological classification uses taxonomic ranks, including among others (in order from most inclusive to least inclusive): Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species, and Strain.[70][note 1]
Taxonomic descriptions
The "definition" of a taxon is encapsulated by its description or its diagnosis or by both combined. There are no set rules governing the definition of taxa, but the naming and publication of new taxa is governed by sets of rules.[8] In zoology, the nomenclature for the more commonly used ranks (superfamily to subspecies), is regulated by the International Code of Zoological Nomenclature (ICZN Code).[71] In the fields of phycology, mycology, and botany, the naming of taxa is governed by the International Code of Nomenclature for algae, fungi, and plants (ICN).[72]
The initial description of a taxon involves five main requirements:[73]
- The taxon must be given a name based on the 26 letters of the Latin alphabet (a binomial for new species, or uninomial for other ranks).
- The name must be unique (i.e. not a homonym).
- The description must be based on at least one name-bearing type specimen.
- It should include statements about appropriate attributes either to describe (define) the taxon or to differentiate it from other taxa (the diagnosis, ICZN Code, Article 13.1.1, ICN, Article 38). Both codes deliberately separate defining the content of a taxon (its circumscription) from defining its name.
- These first four requirements must be published in a work that is obtainable in numerous identical copies, as a permanent scientific record.
However, often much more information is included, like the geographic range of the taxon, ecological notes, chemistry, behavior, etc. How researchers arrive at their taxa varies: depending on the available data, and resources, methods vary from simple quantitative or qualitative comparisons of striking features, to elaborate computer analyses of large amounts of DNA sequence data.[74]
Author citation
An "authority" may be placed after a scientific name.[75] The authority is the name of the scientist or scientists who first validly published the name.[75] For example, in 1758 Linnaeus gave the Asian elephant the scientific name Elephas maximus, so the name is sometimes written as "Elephas maximus Linnaeus, 1758".[76] The names of authors are frequently abbreviated: the abbreviation L., for Linnaeus, is commonly used
Biological taxonomy is a sub-discipline of biology, and is generally practiced by biologists known as "taxonomists", though enthusiastic naturalists are also frequently involved in the publication of new taxa.[67] Because taxonomy aims to describe and organize life, the work conducted by taxonomists is essential for the study of biodiversity and the resulting field of conservation biology.[68][69]
Classifying organisms
