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Encyclopedia > Cladistics
This cladogram shows the relationship among various insect groups.
This cladogram shows the relationship among various insect groups.
Cladograms are tree-like relationship- diagrams.
Cladograms are tree-like relationship- diagrams.

Cladistics is a philosophy of classification that arranges organisms only by their order of branching in an evolutionary tree and not by their morphological similarity, in the words of Luria et al (1981). A major contributor to this school of thought was the German entomologist Willi Hennig, who referred to it as phylogenetic systematics (Hennig, 1979). The word cladistics is derived from the ancient Greek κλάδος, klados, "branch." Image File history File links Please see the file description page for further information. ... A clade is a term belonging to the discipline of cladistics. ... Image File history File links Typical example of a horizontally-oriented cladogram, with horizontal and vertical lines used to indicate relationships. ... Image File history File links Typical example of a horizontally-oriented cladogram, with horizontal and vertical lines used to indicate relationships. ... Image File history File links Typical example of a vertically oriented cladogram, with diagonal intersecting lines indicating relationships. ... Image File history File links Typical example of a vertically oriented cladogram, with diagonal intersecting lines indicating relationships. ... A labeled tree with 6 vertices and 5 edges In graph theory, a tree is a graph in which any two vertices are connected by exactly one path. ... Willi Hennig (April 20, 1913 - November 5, 1976) was a German biologist and is known as the founder of phylogenetic systematics (cladistics). ... A phylogeny (or phylogenesis) is the origin and evolution of a set of organisms, usually of a species. ... In biology, systematics is the study of the diversity of organism characteristics, and especially how they relate evolutionarily. ... Note: This article contains special characters. ...


As the end result of a cladistic analysis, tree-like relationship-diagrams called "cladograms" are drawn up to show hypothesized relationships. A cladistic analysis can be based on as much or as little information as the researcher selects. Modern systematic research is likely to be based on a wide variety of information, including DNA-sequences (so called "molecular data"), biochemical data and morphological data. A labeled tree with 6 vertices and 5 edges In graph theory, a tree is a graph in which any two vertices are connected by exactly one path. ... Comparative anatomy is the study of similarities and differences in organisms. ...


In a cladogram, all organisms lie at the leaves, and each inner node is ideally binary (two-way). The two taxa on either side of a split are called sister taxa or sister groups. Each subtree, whether it contains one item or a hundred thousand items, is called a clade. A natural group has all the organisms contained in any one clade that share a unique ancestor (one which they do not share with any other organisms on the diagram) for that clade. Each clade is set off by a series of characteristics that appear in its members, but not in the other forms from which it diverged. These identifying characteristics of a clade are called synapomorphies (shared, derived characters). For instance, hardened front wings (elytra) are a synapomorphy of beetles, while circinate vernation, or the unrolling of new fronds, is a synapomorphy of ferns. A taxon (plural taxa), or taxonomic unit, is a grouping of organisms (named or unnamed). ... Shared characteristics that define a cladistic grouping. ... Wing structure of a dragonfly (family Gomphidae) Insect wings are outgrowths of the insect exoskeleton that enable insects to fly. ... The elytra of this cockchafer are readily distinguished from the transparent hindwings. ... Suborders Adephaga Archostemata Myxophaga Polyphaga See subgroups of the order Coleoptera Wikispecies has information related to: Coleoptera Beetles are the most diverse group of insects. ... This Australian tree fern is producing a new frond by the process of circinate vernation Vernation (from vernal, since that is when leaves spring forth in Temperate regions) is the formation of new leaves or fronds. ... Classes Psilotopsida Equisetopsida Marattiopsida Polypodiopsida A fern is any one of a group of about 20,000 species of plants classified in the phylum or division Pteridophyta, also known as Filicophyta. ...

Contents

Definitions

A character state (see below) that is present in both the outgroups (the nearest relatives of the group that are not part of the group itself) and in the ancestors is called a plesiomorphy (meaning "close form", also called an ancestral state). A character state that occurs only in later descendants is called an apomorphy (meaning "separate form", also called a "derived" state) for that group. The adjectives plesiomorphic and apomorphic are used instead of "primitive" and "advanced" to avoid placing value-judgments on the evolution of the character states, since both may be advantageous in different circumstances. It is not uncommon to refer informally to a collective set of plesiomorphies as a ground plan for the clade or clades they refer to.


Several more terms are defined for the description of cladograms and the positions of items within them. A species or clade is basal to another clade if it holds more plesiomorphic characters than that other clade. Usually a basal group is very species-poor as compared to a more derived group. It is not a requirement that a basal group be present. For example, when considering birds and mammals together, neither is basal to the other: both have many derived characters. In phylogenetics, basal members of a group are subgroups that diverged very early from the others. ...


A clade or species located within another clade can be described as nested within that clade.


Cladistics as a break with the past

The school of thought now known as cladistics took inspiration from the work of Willi Hennig. But Hennig's major book, even the 1979 version, does not contain the term 'cladistics' in the index. He referred to his own approach as phylogenetic systematics, implied by the book's title (Hennig, 1979). A review paper by Dupuis (1984) observes that the term 'clade' was introduced in 1958 by Julian Huxley, 'cladistic' by Cain and Harrison in 1960 and 'cladist' (for an adherent of Hennig's school) by Mayr in 1965. Some of the debates that the cladists engaged in had been running since the 19th century, but they entered these debates with a new fervor, as can be learned from the Foreword to Hennig (1979) in which Rosen, Nelson and Patterson wrote the following:

Encumbered with vague and slippery ideas about adaptation, fitness, biological species and natural selection, neo-Darwinism (summed up in the "evolutionary" systematics of Mayr and Simpson) not only lacked a definable investigatory method, but came to depend, both for evolutionary interpretation and classification, on consensus or authority. (Foreword, page ix).

Cladistic methods

A cladistic analysis is applied to a certain set of information. To organize this information a distinction is made between characters, and character states. Consider the color of feathers, this may be blue in one species but red in another. Thus, "red feathers" and "blue feathers" are two character states of the character "feather-color."


The researcher decides which character states were present before the last common ancestor of the species group (plesiomorphies) and which were present in the last common ancestor (synapomorphies) by considering one or more outgroups. An outgroup is an organism that is considered not to be part of the group in question, but is closely related to the group. This makes the choice of an outgroup an important task, since this choice can profoundly change the topology of a tree. Note that only synapomorphies are of use in characterising clades.


Next, different possible cladograms are drawn up and evaluated. Clades ideally have many "agreeing" synapomorphies. Ideally there is a sufficient number of true synapomorphies to overwhelm homoplasies caused by convergent evolution (i.e. characters that resemble each other because of environmental conditions or function, not because of common ancestry). A well-known example of homoplasy due to convergent evolution is the character wings. Though the wings of birds and insects may superficially resemble one another and serve the same function, each evolved independently. If a bird and an insect are both accidentally scored "POSITIVE" for the character "presence of wings", a homoplasy would be introduced into the dataset, and this gives a false picture of evolution. It has been suggested that Morphological convergence be merged into this article or section. ...


Many cladograms are possible for any given set of taxa, but one is chosen based on the principle of parsimony: the most compact arrangement, that is, with the fewest character state changes (synapomorphies), is the hypothesis of relationship we tentatively accept (see Occam's razor for more on the principle of parsimony). Though at one time this analysis was done by hand, computers are now used to evaluate much larger data sets. Sophisticated software packages such as PAUP* allow the statistical evaluation of the confidence we have in the veracity of the nodes of a cladogram. Parsimony, in the general sense, means taking extreme care at arriving at a course of action; or unusual or excessive frugality, extreme economy or stinginess. ... William of Ockham Occams razor (also spelled Ockhams razor) is a principle attributed to the 14th-century English logician and Franciscan friar William of Ockham. ... This list of phylogenetics software is a compilation of computational phylogenetics software used to produce phylogenetic trees. ...


As DNA sequencing has become cheaper and easier, molecular systematics has become a more and more popular way to reconstruct phylogenies. Using a parsimony criterion is only one of several methods to infer a phylogeny from molecular data; maximum likelihood and Bayesian inference, which incorporate explicit models of sequence evolution, are non-Hennigian ways to evaluate sequence data. Another powerful method of reconstructing phylogenies is the use of genomic retrotransposon markers, which are thought to be less prone to the reversion and convergence that plagues sequence data. DNA sequencing is the process of determining the nucleotide order of a given DNA fragment, called the DNA sequence. ... It has been suggested that molecular phylogeny be merged into this article or section. ... Maximum likelihood estimation (MLE) is a popular statistical method used to make inferences about parameters of the underlying probability distribution from a given data set. ... Bayesian inference is statistical inference in which evidence or observations are used to update or to newly infer the probability that a hypothesis may be true. ... Retrotransposons as cladistic markers The analysis of SINEs – Short INterspersed Elements – LINEs – Long INterspersed Elements – or truncated LTRs – Long Terminal Repeats – as molecular cladistic markers represents a particularly interesting complement to DNA sequence and morphological data. ...


Ideally, morphological, molecular and possibly other (behavioral etc.) phylogenies should be combined: none of the methods is "superior", but all have different intrinsic sources of error. For example, character convergence (homoplasy) is much more common in morphological data than in molecular sequence data, but character reversions are more common in the latter (see long branch attraction). In evolutionary biology, convergent evolution describes the process whereby organisms not closely related independently acquire similar characteristics while evolving in separate and sometimes varying ecosystems. ... Long branch attraction (LBA) is a phenomenon in phylogenetic analyses (most commonly those employing maximum parsimony) when rapidly evolving lineages are inferred to be closely related, regardless of their true evolutionary relationships. ...


Cladistics does not assume any particular theory of evolution, only the background knowledge of descent with modification. Thus, cladistic methods can be, and recently have been, usefully applied to non-biological systems, including determining language families in historical linguistics and the filiation of manuscripts in textual criticism. Historical linguistics (also diachronic linguistics or comparative linguistics) is primarily the study of the ways in which languages change over time. ... Paternity is the social and legal acknowledgment of the parental relationship between a father and his child. ... Textual criticism or lower criticism is a branch of philology or bibliography that is concerned with the identification and removal of errors from texts. ...


Cladistic classification

Three ways to define a clade for use in a cladistic taxonomy.Node-based: the most recent common ancestor of A and B and all its descendants.Stem-based: all descendants of the oldest common ancestor of A and B that is not also an ancestor of Z.Apomorphy-based: the most recent common ancestor of A and B possessing a certain apomorphy (derived character), and all its descendants.
Three ways to define a clade for use in a cladistic taxonomy.
Node-based: the most recent common ancestor of A and B and all its descendants.
Stem-based: all descendants of the oldest common ancestor of A and B that is not also an ancestor of Z.
Apomorphy-based: the most recent common ancestor of A and B possessing a certain apomorphy (derived character), and all its descendants.

A recent trend in biology since the 1960s, called cladism or cladistic taxonomy, requires taxa to be clades. In other words, cladists argue that the classification system should be reformed to eliminate all non-clades. In contrast, other taxonomists insist that groups reflect phylogenies and often make use of cladistic techniques, but allow both monophyletic and paraphyletic groups as taxa. Types of biological clade, as used in PhyloCode Diagram by User:Gdr File links The following pages link to this file: Cladistics PhyloCode User:Gdr/Gallery Categories: GFDL images ... It has been suggested that Clade be merged into this article or section. ... Evolutionary taxonomy or evolutionary systematics seeks to classify organisms using a combination of phylogenetic relationship and overall similarity. ... In biology, phylogenetics (Greek: phylon = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e. ... In phylogenetics, a group is monophyletic (Greek: of one stem) if all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group. ... Paraphyletic - Wikipedia /**/ @import /skins-1. ... A taxon (plural taxa) is an element of a taxonomy, e. ...


A monophyletic group is a clade, comprising an ancestral form and all of its descendants, and so forming one (and only one) evolutionary group. A paraphyletic group is similar, but excludes some of the descendants that have undergone significant changes. For instance, the traditional class Reptilia excludes birds even though they evolved from the ancestral reptile. Similarly, the traditional Invertebrates are paraphyletic because Vertebrates are excluded, although the latter evolved from an Invertebrate. In phylogenetics, a group is monophyletic (Greek: of one stem) if all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group. ... Paraphyletic - Wikipedia /**/ @import /skins-1. ...


A group with members from separate evolutionary lines is called polyphyletic. For instance, the once-recognized Pachydermata was found to be polyphyletic because elephants and rhinoceroses arose from non-pachyderms separately. Evolutionary taxonomists consider polyphyletic groups to be errors in classification, often occurring because convergence or other homoplasy was misinterpreted as homology. In biology, a taxon is polyphyletic if it is descended from more than one root form (in Greek poly = many and phyletic = racial). ... It has been suggested that Morphological convergence be merged into this article or section. ... In evolutionary biology, convergent evolution describes the process whereby organisms not closely related independently acquire similar characteristics while evolving in separate and sometimes varying ecosystems. ... In biology, two or more structures are said to be homologous if they are alike because of shared ancestry. ...


Following Hennig, cladists argue that paraphyly is as harmful as polyphyly. The idea is that monophyletic groups can be defined objectively, in terms of common ancestors or the presence of synapomorphies. In contrast, paraphyletic and polyphyletic groups are both defined based on key characters, and the decision of which characters are of taxonomic import is inherently subjective. Many argue that they lead to "gradistic" thinking, where groups advance from "lowly" grades to "advanced" grades, which can in turn lead to teleology. In evolutionary studies, teleology is usually avoided because it implies a plan that cannot be empirically demonstrated. Teleology (telos: end, purpose) is the philosophical study of design, purpose, directive principle, or finality in nature or human creations. ...


Going further, some cladists argue that ranks for groups above species are too subjective to present any meaningful information, and so argue that they should be abandoned. Thus they have moved away from Linnaean taxonomy towards a simple hierarchy of clades. The validity of this argument hinges crucially on how often in evolution gradualist near-equilibria are punctuated. A quasi-stable state will result in phylogenies, which may be all but unmappable onto the Linnaean hierarchy, whereas a punctuation event that balances a taxon out of its ecological equilibrium is likely to lead to a split between clades that occurs in comparatively short time and thus lends itself readily for classification according to the Linnaean system. Gradualism, in biology, holds that evolution occurs through the accumulation of slight modifications over a period of generations. ... Punctuated equilibrium, or punctuated equilibria, is a theory of evolution which states that changes such as speciation can occur relatively quickly, with long periods of little change—equilibria—in between. ...


Other evolutionary systematists argue that all taxa are inherently subjective, even when they reflect evolutionary relationships, since living things form an essentially continuous tree. Any dividing line is artificial, and creates both a monophyletic section above and a paraphyletic section below. Paraphyletic taxa are necessary for classifying earlier sections of the tree – for instance, the early vertebrates that would someday evolve into the family Hominidae cannot be placed in any other monophyletic family. They also argue that paraphyletic taxa provide information about significant changes in organisms' morphology, ecology, or life history – in short, that both taxa and clades are valuable but distinct notions, with separate purposes. Many use the term monophyly in its older sense, where it includes paraphyly, and use the alternate term holophyly to describe clades (monophyly in Hennig's sense). As an unscientific rule of thumb, if a distinct lineage that renders the containing clade paraphyletic has undergone marked adaptive radiation and collected many synapomorphies - especially ones that are radical and/or unprecedented -, the paraphyly is usually not considered a sufficient argument to prevent recognition of the lineage as distinct under the Linnaean system (but it is by definition sufficient in phylogenetic nomenclature). For example, as touched upon briefly above, the Sauropsida ("reptiles") and the Aves (birds) are both ranked as a Linnaean class, although the latter are a highly derived offshoot of some forms of the former which themselves were already quite advanced. Adaptive radiation describes the rapid speciation of a single or a few species to fill many ecological niches. ... A synapomorphy is, in evolutionary biology, a derived character-state shared by two or more terminal groups (taxa included in a cladistic analysis as further indivisible units) and inherited from their most recent common ancestor. ... Superclasses Anapsida Eurapsida Diapsida Reptilia was an old kingdom or phylum classification that has since been divided into 4 classes. ... For other meanings of bird, see bird (disambiguation). ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ...


A formal code of phylogenetic nomenclature, the PhyloCode, is currently under development for cladistic taxonomy. It is intended for use by both those who would like to abandon Linnaean taxonomy and those who would like to use taxa and clades side by side. In several instances (see for example Hesperornithes) it has been employed to clarify uncertainties in Linnaean systematics so that in combination they yield a taxonomy that is unambiguously placing the group in the evolutionary tree in a way that is consistent with current knowledge. Types of Clade (Note: Stem-based is now branch-based, to avoid confusion with the term stem group which means total clade minus crown clade.) The PhyloCode is a developing draft for a formal set of rules governing phylogenetic nomenclature. ... Families Enaliornithidae Baptornithidae Hesperornithidae Synonyms Odontornithes Marsh, 1873 (partim) Odontolcae Marsh, 1875 Gaviomorphae Cracraft, 1982 (partim) Hesperornithes are an extinct and highly specialized subclass of Cretaceous toothed birds. ...


See also

The evolutionary tree of living things is currently supposed to run something along the lines of that listed below. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Simplified relationship diagram of molluscs evolution: Cladogram shows hypothetical molluscs evolution. ... Types of Clade (Note: Stem-based is now branch-based, to avoid confusion with the term stem group which means total clade minus crown clade.) The PhyloCode is a developing draft for a formal set of rules governing phylogenetic nomenclature. ... A phylogenetic tree, also called an evolutionary tree or a tree of life, is a tree showing the evolutionary interrelationships among various species or other entities that are believed to have a common ancestor. ... For other uses, see Scientific classification (disambiguation). ...

References

  • Ashlock, Peter D. (1974). "The uses of cladistics". Annual Review of Ecology and Systematics 5: 81-99. 
  • de Queiroz, Kevin; and Jacques A. Gauthier (1992). "Phylogenetic taxonomy". Annual Review of Ecology and Systematics 23: 449–480. 
  • Dupuis, Claude (1984). "Willi Hennig's impact on taxonomic thought". Annual Review of Ecology and Systematics 15: 1-24. ISSN 0066-4162. 
  • Felsenstein, Joseph (2004). Inferring phylogenies. Sunderland, MA: Sinauer Associates. ISBN 0-87893-177-5. 
  • Hamdi, Hamdi; Hitomi Nishio, Rita Zielinski and Achilles Dugaiczyk (1999). "Origin and phylogenetic distribution of Alu DNA repeats: irreversible events in the evolution of primates". Journal of Molecular Biology 289: 861–871. PMID 10369767. 
  • Hennig, Willi (1950). Grundzüge einer Theorie der Phylogenetischen Systematik. Berlin: Deutscher Zentralverlag. .
  • Hennig, Willi (1982). Phylogenetische Systematik (ed. Wolfgang Hennig). Berlin: Blackwell Wissenschaft. ISBN 3-8263-2841-8. 
  • Hennig, Willi (1975). "'Cladistic analysis or cladistic classification': a reply to Ernst Mayr". Systematic Zoology 24: 244-256. 
  • Hennig, Willi (1979). Phylogenetic systematics (tr. D. Dwight Davis and Rainer Zangerl). Urbana, IL: Univ. of Illinois Press (reprinted 1999). ISBN 0-252-06814-9. 
  • Hull, David L. (1979). "The limits of cladism". Systematic Zoology 28: 416-440. 
  • Kitching, Ian J.; Peter L. Forey, Christopher J. Humphries and David M. Williams (1998). Cladistics: Theory and practice of parsimony analysis, 2nd ed.. Oxford University Press. ISBN 0-19-850138-2. 
  • Luria, Salvador; Stephen Jay Gould and Sam Singer (1981). A view of life. Menlo Park, CA: Benjamin/Cummings. ISBN 0-8053-6648-2. 
  • Mayr, Ernst (1982). The growth of biological thought: diversity, evolution and inheritance. Cambridge, MA: Harvard Univ. Press. ISBN 0-674-36446-5. 
  • Patterson, Colin (1982). Joysey, Kenneth A; A. E. Friday (editors) "Morphological characters and homology". Problems in Phylogenetic Reconstruction, London: Academic Press.
  • Rosen, Donn; Gareth Nelson and Colin Patterson (1979), Foreword provided for Hennig (1979)
  • Shedlock, Andrew M; Norihiro Okada (2000). "SINE insertions: Powerful tools for molecular systematics". Bioessays 22: 148–160. PMID 10655034. 
  • Sokal, Robert R. (1975). "Mayr on cladism -- and his critics". Systematic Zoology 24: 257-262. 
  • Swofford, David L; G. J. Olsen, P. J. Waddell and David M. Hillis (1996). Hillis, David M; C. Moritz and B. K. Mable (editors) "Phylogenetic inference". Molecular Systematics, Sunderland, MA: Sinauer Associates.
  • Wiley, Edward O. (1981). Phylogenetics: The Theory and Practice of Phylogenetic Systematics. New York: Wiley Interscience. ISBN 0-471-05975-7. 

ISSN, or International Standard Serial Number, is the unique eight-digit number applied to a periodical publication including electronic serials. ...

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Topics in phylogenetics
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Relevant fields: phylogenetics | computational phylogenetics | molecular phylogeny | cladistics
Basic concepts: synapomorphy | phylogenetic tree | phylogenetic network | long branch attraction
Phylogeny inference methods: maximum parsimony | maximum likelihood | neighbour joining | UPGMA | Bayesian inference
Current topics: PhyloCode | DNA barcoding
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  Results from FactBites:
 
Cladistics - Wikipedia, the free encyclopedia (1727 words)
Cladistics (Greek: klados = branch) is a branch of biology that determines the evolutionary relationships between organisms based on derived similarities.
Thus, cladistic methods can be, and recently have been, usefully applied to non-biological systems, including determining language families in historical linguistics and the filiation of manuscripts in textual criticism.
Stem-based: all descendants of the oldest common ancestor of A and B that is not also an ancestor of Z. Apomorphy-based: the most recent common ancestor of A and B possessing a certain apomorphy (derived character), and all its descendants.
Cladistics - Wikipedia, the free encyclopedia (1348 words)
Cladistics (or phylogenetic systematics) is a branch of biology that seeks to erect classification groups for all organisms, based solely on their evolutionary relationships.
Cladistics has taken a while to settle in, and there is still wide debate over how to apply Henig's ideas in the real world.
Cladistic parsimony is a method of phylogenetic inference in the construction of cladograms.
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