Taxonomy (biology)

Basic, common levels of modern classification of biological diversity. Other levels can be used, and there are proposals for higher levels above domain.

In biology, taxonomy is the science of describing, naming, and classifying living and extinct organisms, with groupings based on shared characteristics. (In a wider sense, the term taxonomy is employed relative to the classification of all things, including inanimate objects, places and events, or to the principles underlying the classification of things.) The framework for organizing the world's immense biological diversity has its foundation in the work of Swedish botanist Carl Linnaeus, who developed a ranked system known as Linnaean taxonomy for categorizing organisms and binomial nomenclature for naming organisms. The Linnaean system is a robust one that has easily been updated and adapted with the availability of more information. The current Linnaean system has been transformed into a system of modern biological classification intended to reflect the evolutionary relationships among organisms, both extant and extinct.

in biology, organisms are grouped into taxa (singular: taxon) and these groups are given a taxonomic rank; groups of a given rank can be aggregated to form a more inclusive group of higher rank, thus creating a taxonomic hierarchy. The principal ranks in modern use are domain, kingdom, phylum (division is sometimes used in botany in place of phylum), class, order, family, genus, and species. The addition of minor ranks, such as subfamily and superfamily, adds to the organizational complexity of the system. There are proposals to extend the system to include non-cellular entities (viruses), which are a major source of biological diversity, and to add such major taxonomic ranks as world and empire to accommodate both viruses and the newly uncovered diversity in unicellular eukaryotes.

An important science, taxonomy is basic to all biological disciplines, since each requires the correct names and descriptions of the organisms being studied. However, taxonomy is also dependent on the information provided by other disciplines, such as genetics, physiology, ecology, and anatomy. The term taxonomy is often used interchangeably with systematics, although the terms are variously also seen as sub-areas of the other.

Naming, describing, and classifying living organisms is a natural and integral activity of humans. Without such knowledge, it would be difficult to communicate, let alone indicate to others what plant is poisonous, what plant is edible, and so forth. The book of Genesis in the Bible references the naming of living things as one of the first activities of humanity. Some further feel that, beyond naming and describing, the human mind naturally organizes its knowledge of the world into systems, and taxonomy also satisfies a desire for humans to see their relatedness to other organisms.

In the later decades of the twentieth century, cladistics, an alternate approach to biological classification, has grown from an idea to an all-encompassing program exerting powerful influence in classification and challenging Linnaean conventions of naming.

Taxonomy, systematics, alpha and beta taxonomy: Defining terms

The term taxonomy is derived from the Greek τάξις/taxis ("arrangement" or "order" from the verb tassein, meaning “to classify”) and -νομία/nomos (“law,” "method," or “science,” such as used in “economy”). The term was introduced in 1813 by Augustin Pyramus de Candolle, in his Théorie élémentaire de la botanique (Singh 2004).

For a long time, the term taxonomy was unambiguous and used for the classification of living and once-living organisms, and the principles, rules and procedures employed in such classification. The use of the term in this sense is sometimes referred to as "biological classification" or "scientific classification," and it involves organization of taxonomic units known as "taxa" (singular "taxon")—a taxonomic group of any rank, such as sub-species, species, family, genus, and so on. Beyond classification, the discipline or science of taxonomy historically included the discovering, naming, and describing of organisms.

Over time, however, the word taxonomy has come to add a broader meaning, referring to the classification of things, or the principles underlying the classification. Almost anything may be classified according to some taxonomic scheme, such as stellar and galactic classifications, or classifications of events and places. In this article, the focus is the narrower usage of taxonomy in terms of biology and biological organisms.

Some definitions of taxonomy, in this narrower and original sense, are presented below:

1. Theory and practice of grouping individuals into species, arranging species into larger groups, and giving those groups names, thus producing a classification (Judd et al. 2007).
2. A field of science (and a major component of systematics) that encompasses description, identification, nomenclature, and classification (Simpson 2010).
3. The science of classification; in biology, the arrangement of organisms into a classification (Kirk et al. 2008).
4. "The science of classification as applied to living organisms, including the study of means of formation of species, etc." (Wordsworth Dictionary 1988).
5. "The analysis of an organism's characteristics for the purpose of classification" (Lawrence 2005).
6. "Systematics studies phylogeny to provide a pattern that can be translated into the classification and names of the more inclusive field of taxonomy" (listed as a desirable but unusual definition) (Wheeler 2004).

The varied definitions either place taxonomy as a sub-area of systematics (definition 2), invert that relationship (definition 6), or appear to consider the two terms synonymous. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy (definitions 1 and 2), or a part of systematics outside taxonomy (Laurin 2023). For example, definition 6 is paired with the following definition of systematics that places nomenclature outside taxonomy (Henderson 2005):

• Systematics: "The study of the identification, taxonomy, and nomenclature of organisms, including the classification of living things with regard to their natural relationships and the study of variation and the evolution of taxa."

In 1970, Michener et al. defined "systematic biology" and "taxonomy" (terms that are often confused and used interchangeably) in relation to one another as follows:

Systematic biology (hereafter called simply systematics) is the field that (a) provides scientific names for organisms, (b) describes them, (c) preserves collections of them, (d) provides classifications for the organisms, keys for their identification, and data on their distributions, (e) investigates their evolutionary histories, and (f) considers their environmental adaptations. This is a field with a long history that in recent years has experienced a notable renaissance, principally with respect to theoretical content. Part of the theoretical material has to do with evolutionary areas (topics e and f above), the rest relates especially to the problem of classification. Taxonomy is that part of Systematics concerned with topics (a) to (d) above.

A whole set of terms including taxonomy, systematic biology, systematics, scientific classification, biological classification, and phylogenetics have at times had overlapping meanings—sometimes the same, sometimes slightly different, but always related and intersecting (Small 1989). However, taxonomy, and in particular alpha taxonomy, is more specifically the identification, description, and naming (i.e., nomenclature) of organisms (Forte 2008), while "classification" focuses on placing organisms within hierarchical groups that show their relationships to other organisms.

In general, the term systematics includes an aspect of phylogenetic analysis (the study of evolutionary relatedness among various groups of organisms). That is, it deals not only with discovering, describing, naming, and classifying living things, but also with investigating the evolutionary relationship between taxa, especially at the higher levels. Thus, according to this perspective, systematics not only includes the traditional activities of taxonomy, but also the investigation of evolutionary relationships, variation, speciation, and so forth. However, as noted above, there remain disagreements on the technical differences between the two terms—taxonomy and systematics—and they are often used interchangeably.

"Alpha taxonomy" is a sub-discipline of taxonomy and is concerned with describing new species, and defining boundaries between species. Activities of alpha taxonomists include finding new species, preparing species descriptions, developing keys for identification, and cataloging the species. While the term alpha taxonomy is primarily used to refer to the discipline of finding, describing, and naming taxa, particularly species, in earlier literature, the term had a different meaning, referring to morphological taxonomy (Rosselló-Mora and Amann 2001). William Bertram Turrill, who introduced the term in a series of papers published in 1935 and 1937, explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy (Turrill 1938). Later authors have used the term in a different sense, to mean the delimitation of species (not subspecies or taxa of other ranks), using whatever investigative techniques are available, and including sophisticated computational or laboratory techniques (Steyskal 1965).

"Beta taxonomy" is another sub-discipline and deals with the arrangement of species into a natural system of classification. Ernst Mayr in 1968 defined "beta taxonomy" as the classification of ranks higher than species (Mayr 1968).

An understanding of the biological meaning of variation and of the evolutionary origin of groups of related species is even more important for the second stage of taxonomic activity, the sorting of species into groups of relatives ("taxa") and their arrangement in a hierarchy of higher categories. This activity is what the term classification denotes; it is also referred to as "beta taxonomy".

Universal codes and scientific nomenclature

Codes have been created to provide a universal and precise system of rules for the taxonomic classification of plants, animals, and bacteria. The International Code of Botanical Nomenclature (ICBN) is the set of rules and recommendations governing the formal botanical names given to plants and fungi. Its intent is that each taxonomic group ("taxon", plural "taxa") of plants has only one correct name, accepted worldwide. The International Code of Zoological Nomenclature (ICZN) is a set of rules in zoology to provide the maximum universality and continuity in the naming of animals. The International Code of Nomenclature of Bacteria (ICNB) governs the scientific names for bacteria.

The following basic rules apply to all three codes (UH 2024):

• Binomial name. Organisms are identified by their binomial name, comprised of the genus and species names (eg, brook trout's scientific name is Salvelinus fontinalis).
• Capitalization and italicization. The genus name is always capitalized, while the species name is not. Both genus and species names are always either italicized or underlined.
• Abbreviation. One can abbreviate genus names by their first letter, but species names cannot be abbreviated (eg. brook trout, Salvelinus fontinalis, can be written as S. fontinalis).
• References to unknown species. Unknown species can be listed with the abbreviation sp. This sp. is not italicized. For example, Danio is a genus of small freshwater fish. Should a new species be discovered, it could be listed as Danio sp.
• References to multiple species in a genus. To refer in general to multiple species within the same genus, one could use the genus name followed by the abbreviation spp, such as a Danio spp. to refer to a group of freshwater fish in the genus Danio. The abbreviation spp. is not italicized.

Most of the binomial names are Latin terms, but some are Greek, and some are derived from the names of their discovers or other personalities. A new species of pacu (a freshwater fish) was recently named Myloplus sauron, with the sauron given because a stripe on its side reminded the researchers of the eye of Sauron, referencing the dark lord Sauron in J.R.R. Tolkien's epic novel Lord of the Rings.

Classifying organisms: Taxonomic rank

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, the relative level of a group of organisms (a taxon) in an ancestral or hereditary hierarchy. A common system of biological classification (taxonomy) consists of species, genus, family, order, class, phylum, kingdom, and domain.

The major ranks: domain, kingdom, phylum, class, order, family, genus, and species, applied to the red fox, Vulpes vulpes.

A given rank subsumes less general categories under it, that is, more specific descriptions of life forms. Above it, each rank is classified within more general categories of organisms and groups of organisms related to each other through inheritance of traits or features from common ancestors. The rank of any species and the description of its genus is basic; which means that to identify a particular organism, it is usually not necessary to specify ranks other than these first two (Turland et al. 2018).

Consider a particular species, the red fox, Vulpes vulpes: the specific name or specific epithet vulpes (small v) identifies a particular species in the genus Vulpes (capital V), which comprises all the "true" foxes. Their close relatives are all in the family Canidae, which includes dogs, wolves, jackals, and all foxes; the next higher major rank, the order Carnivora, includes caniforms (bears, seals, weasels, skunks, raccoons, and all those mentioned above), and feliforms (cats, civets, hyenas, mongooses). Carnivorans are one group of the hairy, warm-blooded, nursing members of the class Mammalia, which are classified among animals with notochords in the phylum Chordata, and with them among all animals in the kingdom Animalia. Finally, at the highest rank all of these are grouped together with all other organisms possessing cell nuclei in the domain Eukarya.

Main ranks

In his landmark publications, such as the Systema Naturae, Carl Linnaeus utilized the ranks of kingdom, class, order, genus, species, and one rank below species. However, the Linnaean Natural System is a flexible one, and today there are seven main taxonomic ranks: kingdom, phylum or division, class, order, family, genus, and species. In addition, domain (proposed by Carl Woese et al. 1990) is now widely used as a fundamental rank, although it has not been canonized by any of the international taxonomic committee/nomenclature codes (van der Gulik et al. 2023), and is a synonym for dominion, introduced by Moore in 1974 (Moore 1974). More recently, van der Gulik et al. (2023) proposed to extend the Linnaean system to include the named rank of world (Latin alternative mundus) to include non-cellular entities (viruses) and empire (or imperium) to better delineate the diversity within unicellular eukaryotes. [Empire had also been proposed by Mayr (1998) and Woese (1998) as an alternative name for domain.]

Main taxonomic ranks

Latin	English
regio	domain
regnum	kingdom
phylum	phylum (in zoology) / division (in botany)
classis	class
ordo	order
familia	family
genus	genus
species	species

A taxon is usually assigned a rank when it is given its formal name. The basic ranks are species and genus. When an organism is given a species name it is assigned to a genus, and the genus name is part of the species name.

Domain and Kingdom systems

At the top of the typical taxonomic classification of organisms, one can find either Domain or Kingdom.

For two centuries, from the mid-eighteenth century until the mid-twentieth century, organisms were generally considered to belong to one of two kingdoms, Plantae (plants, including bacteria) or Animalia (animals, including protozoa). This system, proposed by Carolus Linnaeus in the mid-eighteenth century, had obvious difficulties, including the problem of placing fungi, protists, and prokaryotes. There are single-celled organisms that fall between the two categories, such as Euglena, that can photosynthesize food from sunlight and, yet, feed by consuming organic matter.

In 1969, American ecologist Robert H. Whittaker proposed a system with five kingdoms: Monera (prokaryotes—bacteria and blue-green algae), Protista (unicellular, multicellular, and colonial protists), Fungi, Plantae, and Animalia. This system was widely used for three decades but is largely abandoned today (van der Gulik 2023).

More recently, the "domain," a classification level higher than kingdom, has been devised. Also called a "Superregnum" or "Superkingdom," domain is the top-level grouping of organisms in scientific classification. One of the reasons such a classification has been developed is because research has revealed the unique nature of anaerobic bacteria (called Archaeobacteria, or simply Archaea). These "living fossils" are genetically and metabolically very different from oxygen-breathing organisms. Various numbers of Kingdoms are recognized under the domain category.

In the three-domain system, which was introduced by Carl Woese in 1990 (Woese et al. 1990), the three groupings are: Archaea; Bacteria; and Eukaryota. This scheme emphasizes the separation of prokaryotes into two groups, the Bacteria (originally labelled Eubacteria) and the Archaea (originally labeled Archaebacteria).

In some classifications, authorities keep the kingdom as the higher-level classification, but recognize a sixth kingdom, the Archaebacteria.

Coexisting with these schemes is yet another scheme that divides living organisms into the two main categories (empires) of prokaryote (cells that lack a Nucleus: Bacteria and so on) and eukaryote (cells that have a nucleus and membrane-bound organelles: Animals, plants, fungi, and protists).

In summary, today there are several competing top classifications of life, including:

• The three-domain system of Carl Woese, with top-level groupings of Archaea, Eubacteria, and Eukaryota domains
• The two-empire system, with top-level groupings of Prokaryota (or Monera) and Eukaryota empires
• The five-kingdom system with top-level groupings of Monera, Protista, Fungi, Plantae, and Animalia
• The six-kingdom system with top-level groupings of Archaebacteria, Monera, Protista, Fungi, Plantae, and Animalia

Ranks in zoology

There are definitions of the following taxonomic ranks in the International Code of Zoological Nomenclature: superfamily, family, subfamily, tribe, subtribe, genus, subgenus, species, subspecies.

The International Code of Zoological Nomenclature defines rank as: "The level, for nomenclatural purposes, of a taxon in a taxonomic hierarchy (e.g. all families are for nomenclatural purposes at the same rank, which lies between superfamily and subfamily)."

The International Code of Zoological Nomenclature divides names into "family-group names", "genus-group names" and "species-group names". The Code explicitly mentions the following ranks for these categories:^:§29–31

• Family-groups
  • Superfamily (-oidea)
  • Family (-idae)
  • Subfamily (-inae)
  • Tribe (-ini)
  • Subtribe (-ina)
• Genus-groups
  • Genus
  • Subgenus
• Species-groups
  • Species
  • Subspecies

The rules in the Code apply to the ranks of superfamily to subspecies, and only to some extent to those above the rank of superfamily. Among "genus-group names" and "species-group names" no further ranks are officially allowed. Zoologists sometimes use additional terms such as species group, species subgroup, species complex and superspecies for convenience as extra, but unofficial, ranks between the subgenus and species levels in taxa with many species, e.g. the genus Drosophila. (Note the potentially confusing use of "species group" as both a category of ranks as well as an unofficial rank itself.^{[citation needed]})

At higher ranks (family and above) a lower level may be denoted by adding the prefix "infra", meaning lower, to the rank. For example, infraorder (below suborder) or infrafamily (below subfamily).

Ranks in botany

Botanical ranks categorize organisms based on their relationships. They start with Kingdom, then move to Division (or Phylum), Class, Order, Family, Genus, and Species. Each rank reflects shared characteristics and evolutionary history. Understanding these ranks aids in taxonomy and studying biodiversity.

Ranks in ICN^:{{{1}}}

Rank	Type	Suffix
kingdom (regnum)	primary	N/A
subregnum	further	N/A
division (divisio) phylum (phylum)	primary	‑phyta -mycota (fungi)
subdivisio or subphylum	further	‑phytina -mycotina (fungi)
class (classis)	primary	‑opsida (plant) ‑phyceae (algae) -mycetes (fungi)
subclassis	further	‑idae (plant) ‑phycidae (algae) -mycetidae (fungi)
order (ordo)	primary	-ales
subordo	further	-ineae
family (familia)	primary	-aceae
subfamilia	further	‑oideae
tribe (tribus)	secondary	-eae
subtribus	further	‑inae
genus (genus)	primary	N/A
subgenus	further	N/A
section (sectio)	secondary	N/A
subsectio	further	N/A
series (series)	secondary	N/A
subseries	further	N/A
species (species)	primary	N/A
subspecies	further	N/A
variety (varietas)	secondary	N/A
subvarietas	further	N/A
form (forma)	secondary	N/A
subforma	further	N/A

There are definitions of the following taxonomic categories in the International Code of Nomenclature for Cultivated Plants: cultivar group, cultivar, grex.

The rules in the ICN apply primarily to the ranks of family and below, and only to some extent to those above the rank of family. Template:Crossref

Names of botanical taxa

Taxa at the rank of genus and above have a botanical name in one part (unitary name); those at the rank of species and above (but below genus) have a botanical name in two parts (binary name); all taxa below the rank of species have a botanical name in three parts (an infraspecific name). To indicate the rank of the infraspecific name, a "connecting term" is needed. Thus Poa secunda subsp. juncifolia, where "subsp". is an abbreviation for "subspecies", is the name of a subspecies of Poa secunda.

Examples

The usual classifications of five representative species follow: the fruit fly so familiar in genetics laboratories (Drosophila melanogaster); humans (Homo sapiens); the peas used by Gregor Mendel in his discovery of genetics (Pisum sativum); the fly agaric mushroom Amanita muscaria; and the bacterium Escherichia coli. The eight major ranks are given in bold; a selection of minor ranks is given as well.

Rank	Fruit fly	Human	Pea	Fly Agaric	E. coli
Domain	Eukarya	Eukarya	Eukarya	Eukarya	Bacteria
Kingdom	Animalia	Animalia	Plantae	Fungi	Monera
Phylum or Division	Arthropoda	Chordata	Magnoliophyta	Basidiomycota	Eubacteria
Subphylum or subdivision	Hexapoda	Vertebrata	Magnoliophytina	Hymenomycotina
Class	Insecta	Mammalia	Magnoliopsida	Homobasidiomycetae	Proteobacteria
Subclass	Pterygota	Placentalia	Magnoliidae	Hymenomycetes
Order	Diptera	Primates	Fabales	Agaricales	Enterobacteriales
Suborder	Brachycera	Haplorrhini	Fabineae	Agaricineae
Family	Drosophilidae	Hominidae	Fabaceae	Amanitaceae	Enterobacteriaceae
Subfamily	Drosophilinae	Homininae	Faboideae	Amanitoideae
Genus	Drosophila	Homo	Pisum	Amanita	Escherichia
Species	D. melanogaster	H. sapiens	P. sativum	A. muscaria	E. coli

Notes:

• Botanists and mycologists use systematic naming conventions for taxa higher than genus by combining the Latin stem of the type genus for that taxon with a standard ending characteristic of the particular rank. (See below for a list of standard endings.) For example, the rose family Rosaceae is named after the stem "Ros-" of the type genus Rosa plus the standard ending "-aceae" for a family.
• Zoologists use similar conventions for higher taxa, but only up to the rank of superfamily.
• Higher taxa and especially intermediate taxa are prone to revision as new information about relationships is discovered. For example, the traditional classification of primates (class Mammalia—subclass Theria—infraclass Eutheria—order Primates) is challenged by new classifications such as McKenna and Bell (class Mammalia—subclass Theriformes— infraclass Holotheria—order Primates). These differences arise because there are only a small number of ranks available and a large number of proposed branching points in the fossil record.
• Within species, further units may be recognized. Animals may be classified into subspecies (for example, Homo sapiens sapiens, modern humans). Plants may be classified into subspecies (for example, Pisum sativum subsp. sativum, the garden pea) or varieties (for example, Pisum sativum var. macrocarpon, snow pea), with cultivated plants getting a cultivar name (for example, Pisum sativum var. macrocarpon "Snowbird"). Bacteria may be classified by strains (for example Escherichia coli O157:H7, a strain that can cause food poisoning).

Group suffixes

Taxa above the genus level are often given names derived from the Latin (or Latinized) stem of the type genus, plus a standard suffix. The suffixes used to form these names depend on the kingdom, and sometimes the phylum and class, as set out in the table below.

Rank	Plants	Algae	Fungi	Animals
Division/Phylum	-phyta		-mycota
Subdivision/Subphylum	-phytina		-mycotina
Class	-opsida	-phyceae	-mycetes
Subclass	-idae	-phycidae	-mycetidae
Superorder	-anae
Order	-ales
Suborder	-ineae
Infraorder	-aria
Superfamily	-acea			-oidea
Family	-aceae			-idae
Subfamily	-oideae			-inae
Tribe	-eae			-ini
Subtribe	-inae			-ina

Notes

• The stem of a word may not be straightforward to deduce from the nominative form as it appears in the name of the genus. For example, Latin "homo" (human) has stem "homin-", thus Hominidae, not "Homidae".
• For animals, there are standard suffixes for taxa only up to the rank of superfamily (ICZN article 27.2).

Historical developments

Classification of organisms is a natural activity of humans and may be the oldest science, as humans needed to classify plants as edible or poisonous, snakes and other animals as dangerous or harmless, and so forth.

The earliest known system of classifying forms of life comes from the Greek philosopher Aristotle, who classified animals based on their means of transportation (air, land, or water), and into those that have red blood and have live births and those that do not. Aristotle divided plants into trees, shrubs, and herbs (although his writings on plants have been lost).

In 1172, Ibn Rushd (Averroes), who was a judge (Qadi) in Seville, translated and abridged Aristotle's book de Anima (On the Soul) into Arabic. His original commentary is now lost, but its translation into Latin by Michael Scot survives.

An important advance was made by the Swiss professor, Conrad von Gesner (1516–1565). Gesner's work was a critical compilation of life known at the time.

The exploration of parts of the New World next brought to hand descriptions and specimens of many novel forms of animal life. In the latter part of the sixteenth century and the beginning of the seventeenth, careful study of animals commenced, which, directed first to familiar kinds, was gradually extended until it formed a sufficient body of knowledge to serve as an anatomical basis for classification. Advances in using this knowledge to classify living beings bear a debt to the research of medical anatomists, such as Hieronymus Fabricius (1537 – 1619), Petrus Severinus (1580 – 1656), William Harvey (1578 – 1657), and Edward Tyson (1649 – 1708). Advances in classification due to the work of entomologists and the first microscopists is due to the research of people like Marcello Malpighi (1628 – 1694), Jan Swammerdam (1637 – 1680), and Robert Hooke (1635 – 1702).

John Ray (1627 – 1705) was an English naturalist who published important works on plants, animals, and natural theology. The approach he took to the classification of plants in his Historia Plantarum was an important step towards modern taxonomy. Ray rejected the system of dichotomous division by which species were classified according to a pre-conceived, either/or type system, and instead classified plants according to similarities and differences that emerged from observation.

Linnaeus

Two years after John Ray's death, Carolus Linnaeus (1707–1778) was born. His great work, the Systema Naturae, ran through twelve editions during his lifetime (1st ed. 1735). In this work nature was divided into three realms: mineral, vegetable, and animal. Linnaeus used four ranks: class, order, genus, and species. He consciously based his system of nomenclature and classification on what he knew of Aristotle (Hull 1988).

Linnaeus is best known for his introduction of the method still used to formulate the scientific name of every species. Before Linnaeus, long, many-worded names had been used, but as these names gave a description of the species, they were not fixed. By consistently using a two-word Latin name—the genus name followed by the specific epithet—Linnaeus separated nomenclature from taxonomy. This convention for naming species is referred to as binomial nomenclature.

Classification after Linnaeus

Some major developments in the system of taxonomy since Linnaeus were the development of different ranks for organisms and codes for nomenclature (see Domain and Kingdom systems, and Universal Codes above), and the inclusion of Darwinian concepts in taxonomy.

According to Hull (1988), "in its heyday, biological systematics was the queen of the sciences, rivaling physics." Lindroth (1983) referenced it as the "most lovable of the sciences." But at the time of Darwin, taxonomy was not held in such high regard as it was earlier. It gained new prominence with the publication of Darwin's The Origin of Species, and particularly since the Modern Synthesis. Since then, although there have been, and continue to be, debates in the scientific community over the usefulness of phylogeny in biological classification, it is generally accepted by taxonomists today that classification of organisms should reflect or represent phylogeny, via the Darwinian principle of common descent.

A vertical orientation yields a cladogram reminiscent of a tree.

Taxonomy remains a dynamic science, with developing trends, diversity of opinions, and clashing doctrines. Two of these competing groups that formed in the 1950s and 1960s were the pheneticists and cladists.

Begun in the 1950s, the pheneticists prioritized quantitative or numerical analysis and the recognition of similar characteristics among organisms over the alternative of speculating about process and making classifications based on evolutionary descent or phylogeny.

Cladistic taxonomy or cladism groups organisms by evolutionary relationships, and arranges taxa in an evolutionary tree. Most modern systems of biological classification are based on cladistic analysis. Cladistics is the most prominent of several taxonomic systems, which also include approaches that tend to rely on key characters (such as the traditional approach of evolutionary systematics, as advocated by G. G. Simpson and E. Mayr). Willi Hennig (1913-1976) is widely regarded as the founder of cladistics.

References

ISBN links support NWE through referral fees

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