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A clade (from Ancient Greek: κλάδος, klados, "branch"), also known as monophyletic group, is a group of organisms that consists of a common ancestor and all its lineal descendants, and represents a single "branch" on the "tree of life".[1] The common ancestor may be an individual, a population, a species (extinct or extant), and so on right up to a kingdom and further. Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over the last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms.[2] Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic. Some of the relationships between organisms that the molecular biology arm of cladistics has revealed are that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria, and multicellular organisms may have evolved from archaea.[3]

Contents

1 Etymology 2 History of nomenclature and taxonomy 3 Definitions 4 Clades and phylogenetic trees 5 Terminology 6 In popular culture 7 See also 8 Notes 9 References 10 External links

Etymology[edit] The term "clade" was coined in 1957 by the biologist Julian Huxley
Julian Huxley
to refer to the result of cladogenesis, a concept Huxley borrowed from Bernhard Rensch.[4][5] Many commonly named groups, rodents and insects for example, are clades because, in each case, the group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant, each of which consists of even smaller clades. The clade "rodent" is in turn included in the mammal, vertebrate and animal clades.

History of nomenclature and taxonomy[edit] Early phylogenetic tree by Haeckel, 1866. Groups once thought to be more advanced, such as birds ("Aves"), are placed at the top. The idea of a clade did not exist in pre-Darwinian Linnaean taxonomy, which was based by necessity only on internal or external morphological similarities between organisms – although as it happens, many of the better known animal groups in Linnaeus' original Systema Naturae
Systema Naturae
(notably among the vertebrate groups) do represent clades. The phenomenon of convergent evolution is, however, responsible for many cases where there are misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life. The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. Thomas Henry Huxley, an early advocate of evolutionary theory, proposed a revised taxonomy based on clades.[6] For example, he grouped birds with reptiles, based on fossil evidence.[6] German biologist Emil Hans Willi Hennig
Emil Hans Willi Hennig
(1913 – 1976) is considered to be the founder of cladistics.[7] He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on a "ladder", with supposedly more "advanced" organisms at the top.[2][8] Taxonomists have increasingly worked to make the taxonomic system reflect evolution.[8] When it comes to naming, however, this principle is not always compatible with the traditional rank-based nomenclature. In the latter, only taxa associated with a rank can be named, yet there are not enough ranks to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it is still controversial.

Definitions[edit] Gavialidae, Crocodylidae and Alligatoridae are clade names that are here applied to a phylogenetic tree of crocodylians. A clade is by definition monophyletic, meaning that it contains one ancestor (which can be an organism, a population, or a species) and all its descendants.[note 1][9][10] The ancestor can be known or unknown; any and all members of a clade can be extant or extinct.

Clades and phylogenetic trees[edit] Main article: Phylogenetics Main article: Cladistics The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics, the latter term coined by Ernst Mayr
Ernst Mayr
(1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms; they, and all their branches, are phylogenetic hypotheses.[11] Three methods of defining clades are featured in phylogenetic nomenclature: node-, stem-, and apomorphy-based (see here for detailed definitions).

Terminology[edit] Cladogram
Cladogram
of modern primate groups; all tarsiers are haplorhines, but not all haplorhines are tarsiers; all apes are catarrhines, but not all catarrhines are apes; etc. The relationship between clades can be described in several ways:

A clade located within a clade is said to be nested within that clade. In the diagram, the hominoid clade, i.e. the apes and humans, is nested within the primate clade. Two clades are sisters if they have an immediate common ancestor. In the diagram, lemurs and lorises are sister clades, while humans and tarsiers are not. A clade A is basal to a clade B if A branches off the lineage leading to B before the first branch leading only to members of B. In the adjacent diagram, the strepsirrhine/prosimian clade, is basal to the hominoids/ape clade. However, in this example, both Haplorrhine as prosimians should be considered as most basal groupings. It is better to say that the prosimians are the sister group to the rest of the primates.[12] This way one also avoids unintended and misconceived connotations about evolutionary advancement, complexity, diversity, ancestor status, and ancienity e.g. due to impact of sampling diversity and extinction.[citation needed][12][13] Basal clades should not be confused with stem groupings, as the latter is associated with paraphyletic or unresolved groupings. In popular culture[edit] Clade
Clade
is the title of a novel by James Bradley, who chose it both because of its biological meaning and also because of the larger implications of the word.[14] An episode of Elementary was titled "Dead Clade
Clade
Walking" and dealt with a case involving a rare fossil.

See also[edit]

Adaptive radiation Binomial nomenclature Biological classification Cladistics Crown group Monophyly Paraphyly Phylogenetic network Phylogenetic nomenclature Phylogenetics Polyphyly

Notes[edit]

^ A semantic case has been made that the name should be "holophyletic", but this term has not acquired widespread use. For more information, see holophyly.

References[edit]

^ Cracraft, Joel; Donoghue, Michael J., eds. (2004). "Introduction". Assembling the Tree of Life. Oxford University Press. p. 1. ISBN 978-0-19-972960-9..mw-parser-output cite.citation font-style:inherit .mw-parser-output .citation q quotes:"""""""'""'" .mw-parser-output .citation .cs1-lock-free a background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center .mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center .mw-parser-output .citation .cs1-lock-subscription a background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center .mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration color:#555 .mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span border-bottom:1px dotted;cursor:help .mw-parser-output .cs1-ws-icon a background:url("//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png")no-repeat;background-position:right .1em center .mw-parser-output code.cs1-code color:inherit;background:inherit;border:inherit;padding:inherit .mw-parser-output .cs1-hidden-error display:none;font-size:100% .mw-parser-output .cs1-visible-error font-size:100% .mw-parser-output .cs1-maint display:none;color:#33aa33;margin-left:0.3em .mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format font-size:95% .mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left padding-left:0.2em .mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right padding-right:0.2em

^ a b Palmer, Douglas (2009). Evolution: The Story of Life. Berkeley: University of California Press. p. 13.

^ Pace, Norman R. (18 May 2006). "Time for a change". Nature. 441 (7091): 289. Bibcode:2006Natur.441..289P. doi:10.1038/441289a. ISSN 1476-4687. PMID 16710401.

^ Dupuis, Claude (1984). "Willi Hennig's impact on taxonomic thought". Annual Review of Ecology and Systematics. 15: 1–24. doi:10.1146/annurev.es.15.110184.000245.

^ Huxley, J. S. (1957). "The three types of evolutionary process". Nature. 180 (4584): 454–455. Bibcode:1957Natur.180..454H. doi:10.1038/180454a0.

^ a b Huxley, T.H. (1876): Lectures on Evolution. New York Tribune. Extra. no 36. In Collected Essays IV: pp 46-138 original text w/ figures

^ Brower, Andrew V. Z. (2013). "Willi Hennig at 100". Cladistics. 30 (2): 224–225. doi:10.1111/cla.12057.

^ a b ” Evolution
Evolution
101.” page 10. Understanding Evolution
Evolution
website. University of California, Berkeley. Retrieved 26 February 2016.

^ "International Code of Phylogenetic Nomenclature. Version 4c. Chapter I. Taxa". 2010. Retrieved 22 September 2012.

^ Envall, Mats (2008). "On the difference between mono-, holo-, and paraphyletic groups: a consistent distinction of process and pattern". Biological Journal of the Linnean Society. 94: 217. doi:10.1111/j.1095-8312.2008.00984.x.

^ Nixon, Kevin C.; Carpenter, James M. (1 September 2000). "On the Other "Phylogenetic Systematics"". Cladistics. 16 (3): 298–318. doi:10.1111/j.1096-0031.2000.tb00285.x.

^ a b Krell, F.-T. & Cranston, P. (2004). "Which side of the tree is more basal?". Systematic Entomology. 29 (3): 279–281. doi:10.1111/j.0307-6970.2004.00262.x.

^ Smith, Stacey (19 September 2016). "For the love of trees: The ancestors are not among us". For the love of trees. Retrieved 23 March 2019.

^ "Choosing the Book title 'Clade'". Penguin Group Australia. 2015. Retrieved 20 January 2015.

External links[edit]

Look up clade in Wiktionary, the free dictionary. Evolving Thoughts: Clade DM Hillis, D Zwickl & R Gutell. "Tree of life". An unrooted cladogram depicting around 3000 species. Phylogenetic systematics, an introductory slide-show on evolutionary trees University of California, Berkeley vtePhylogeneticsRelevant fields Computational phylogenetics Molecular phylogenetics Cladistics Taxonomy (biology) Evolutionary taxonomy Basic concepts Phylogenesis Cladogenesis Phylogenetic tree Cladogram Phylogenetic network Long branch attraction Clade
Clade
vs Grade Lineage Ghost lineage Ghost population Inference methods Maximum parsimony Probabilistic methods Maximum likelihood Bayesian inference Distance-matrix methods Neighbor-joining UPGMA Least squares Three-taxon analysis Current topics PhyloCode DNA barcoding Molecular phylogenetics Phylogenetic comparative methods Phylogenetic niche conservatism Phylogenetics
Phylogenetics
software Phylogenomics Phylogeography Group traits Primitive Plesiomorphy Symplesiomorphy Derived Apomorphy Synapomorphy Autapomorphy Group types Monophyly Paraphyly Polyphyly Nomenclature Phylogenetic nomenclature Crown group Sister group Basal Supertree

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