 This cladogram shows the relationship among various insect groups. In some cladograms, the length of the horizontal lines indicates time elapsed since the last common ancestor. Cladistics (Greek: clados = branch) is the most prominent of several methods of phylogenetic systematics (Greek: phyle = tribe, race and genetikos = relative to birth, from genesis = birth). Phylogenetic systematics occupies itself by researching evolutionary relationships, by descent, of living things (see biology). Cladistics is a method of rigorous analysis, using "shared derived properties" (synapomorphies: see below). Cladistic analysis forms the basis for most modern systems of classification, which seek to group organisms by evolutionary relationships. In contrast, phenetics groups organisms based on their overall similarity, while more traditional approaches tend to rely on key characters. Willi Hennig is widely regarded as the founder of cladistics. Image File history File links Typical example of a horizontally-oriented cladogram, with horizontal and vertical lines used to indicate relationships. ...
Jump to: navigation, search Charles Darwin, father of the theory of evolution by natural selection. ...
Main articles: Life All organisms (viruses not included) consist of cells, which in turn, are based on a common carbon-based biochemistry. ...
In biology, phenetics, also known as numerical taxonomy, is an attempt to classify organisms based on overall similarity, usually in morphology or other observable traits, regardless of their phylogeny or evolutionary relation. ...
Willi Hennig (April 20, 1913 - November 5, 1976) was a German biologist and is known as the founder of phylogenetic systematics (cladistics). ...
Introduction Based on a wide variety of information, including genetic analysis, biochemical analysis, and analysis of morphology, treelike relationship-diagrams called "cladograms" are drawn up to show different relationship possibilities. Morphology is the following: In linguistics, morphology is the study of the structure of word forms. ...
A 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. ...
 A vertical orientation yields a cladogram reminiscent of a tree. 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 correct cladogram 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 are a synapomorphy of beetles, while circinate vernation, or the unrolling of new fronds, is a synapomorphy of ferns. Image File history File links Typical example of a vertically oriented cladogram, with diagonal intersecting lines indicating relationships. ...
A 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. ...
A taxon (plural taxa) is an element of a taxonomy, e. ...
Shared characteristics that define a cladistic grouping. ...
A Laughing Gull on the beach in Atlantic City. ...
Jump to: navigation, search Suborders Adephaga Archostemata Myxophaga Polyphaga See subgroups of the order Coleoptera Beetles are one of the main groups 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. ...
Jump to: navigation, search Classes Marattiopsida Osmundopsida Gleicheniopsida Pteridopsida A fern, or pteridophyte, is any one of a group of some twenty thousand species of plants classified in the Division Pteridophyta, formerly known as Filicophyta. ...
Definitions Several more terms are defined for the description of cladograms and the positions of items within them. In an upright cladogram (one with species listed at the top, and a "root" at the bottom), a species or clade is basal to another clade if it branches off toward the bottom, or below the other group in question. Conversely, one clade or species can be described as nested within another clade. Thus in a cladogram that includes four mammals and a bird, the bird's branch is basal, but a dog would be nested within the mammals. Similarly, a character-state (see below) that is present in an ancestor of a group is called a plesiomorphy ('primitive' or ancestral state), and one that evolved later is called an apomorphy ("derived" state). The adjectives plesiomorphic and apomorphic are used instead of "primitive" and "advanced" to avoid placing value-judgements on the evolution of the character states.
Cladistic methods Typically, a cladistic analysis begins by collecting information on certain features of all the organisms in question. Features may come in different versions (e.g. feather-color may be blue in one species but red in another). These features are collectively called characters, and specific versions are called character states. Thus, "red feathers" and "blue feathers" are two character states of the character "feather-color."
After recording several character states, the researcher decides which ones were present before the last common ancestor of the species group (symplesiomorphies) and which were present in the last common ancestor (synapomorphies). Usually this is done by considering some outgroup of organisms known to not be too closely related to any of the organisms in question. Only synapomorphies are of any use in characterising cladistic divisions.
Next, different possible cladograms are drawn up and evaluated. Clades are typically drawn to have as many synapomorphies as possible. The hope is that a sufficiently large number of true synapomorphies will be large enough to overwhelm any unintended symplesiomorphies (homeoplasies), 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 convergent evolution is wings. Though the wings of birds and insects may superficially resemble one another and serve the same function, each evolved independently from the other). If a bird and an insect are both accidentally scored "POSITIVE" for the character "presence of wings", a homeoplasy would be introduced into the dataset, which may cause erroneous results. 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 practice, neutral features like exact ultrastructure (a term for extremely fine structure, microscopic or molecular composition of cellular structure) may be used to provide evidence for real relationships even when the appearance of organisms makes it otherwise difficult. When equivalent possibilities turn up, one is usually chosen based on the principle of parsimony: the most compact arrangement is likely the best (a variation of Occam's razor). Another approach, particularly useful in molecular evolution, is maximum likelihood, which selects the optimal cladogram that has the highest likelihood based on a specific probability model of changes. Occams Razor (also spelled Ockhams Razor), is a principle attributed to the 14th-century English logician and Franciscan friar, William of Ockham. ...
Maximum likelihood estimation (MLE) is a popular statistical method used to make inferences about parameters of the underlying probability distribution of a given data set. ...
Cladistics has taken a while to settle in, and there is still wide debate over how to apply Hennig's ideas in the real world. In particular, apomorphies are not always easy to distinguish and data are often unavailable due to a sparsity of available forms or a lack of knowledge of characters, and these may invalidate cladograms. There is also concern that use of widely different data sets (for instance, structural versus genetic characteristics) may produce widely different trees. However, by and large, the phylogenetic approach to systematics has proven useful and coherent and has gained general support.
As DNA sequencing has become easier, phylogenies are increasingly constructed with the aid of molecular data. Computational systematics allows the use of these large data sets to construct objective phylogenies. These can filter out true synapomorphy from parallel evolution more accurately. Space-filling model of a section of DNA molecule Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life (and many viruses). ...
Molecular systematics is a product of the traditional field of systematics and the growing field of bioinformatics. ...
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, by means of examining languages which are recognizably related through similarities such as vocabulary, word formation, and syntax, as well as the surviving records of ancient languages. ...
Textual criticism is a branch of philology that examines the extant manuscript copies of an ancient or medieval literary work to produce a text that is as close as possible to the original. ...
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. A recent trend in biology since the 1960s, called cladism or cladistic taxonomy, has been to require taxa to be clades. In other words cladists argue that the classification system should be reformed to eliminate all non-clades. In contrast, other evolutionary 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 ...
This cladogram shows the relationship among various insect groups. ...
In biology, Phylogenetics (Greek: phylon = race and genetic = birth) is the taxonomical classification of organisms based on how closely they are related in terms of evolutionary differences. ...
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). ...
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 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. Teleology should be avoided as outside the realm of science. Teleology is the supposition that there is design, purpose, directive principle, or finality in the works and processes of nature, and the philosophical study of that purpose. ...
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.
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 can not 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).
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. Types of clade PhyloCode is a draft for a formal set of rules governing phylogenetic nomenclature. ...
See also Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms. ...
The evolutionary tree of living things is currently supposed to run something along the lines of that listed below. ...
A phylogenetic tree is a tree showing the evolutionary interrelationships among various species or other entities that are believed to have a common ancestor. ...
Systematics is the term used by John G Bennett for the study of multi-term systems. ...
Taxonomy (from Greek ταξινομία (taxinomia) from the words taxis = order and nomos = law) may refer to either the classification of things, or the principles underlying the classification. ...
Willi Hennig (April 20, 1913 - November 5, 1976) was a German biologist and is known as the founder of phylogenetic systematics (cladistics). ...
Jump to: navigation, search // Aerobiology Blackley, C. H. (1873) Experimental Researches on the Causes and Nature of Catarrhus Aestivus (Hay-Fever or Hay-Asthma), (Oxford Historical Books). ...
References - Kitching IJ, Forey PL, Humphries CJ and Williams DM (1998) Cladistics, 2nd edn. Oxford: Oxford University Press.
- Patterson C (1982) Morphological characters and homology. In: Joysey KA and Friday AE (eds) Problems in Phylogenetic Reconstruction. London: Academic Press.
- Swofford DL, Olsen GJ, Waddell PJ and Hillis DM (1996) Phylogenetic inference. In: Hillis DM, Moritz C and Mable BK (eds) Molecular Systematics. Sunderland, MA: Sinauer Associates.
- de Quieroz K and Gauthier JA (1992) Phylogenetic taxonomy. Annual Review of Ecology and Systematics 23: 449–480.
- Wiley EO (1981) Phylogenetics: The Theory and Practice of Phylogenetic Systematics. New York: Wiley Interscience.
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