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In cladistics, an autapomorphy is a distinctive anatomical feature, known as a derived trait, that is unique to a given terminal group. That is, it is found only in one member of a clade, but not found in any others or outgroup taxa, not even those most closely related to the group (which may be a species, family or in general any clade).〔Futuyma, Douglas J. ''Evolutionary Biology.'' Sinauer Associaties, Inc., 3rd edition. 1998. Page 95.〕 It can therefore be considered an apomorphy in relation to a single taxon.〔Appel, Ron D.; Feytmans, Ernest. ''Bioinformatics: a Swiss Perspective.'' "Chapter 3: Introduction of Phylogenetics and its Molecular Aspects." World Scientific Publishing Company, 1st edition. 2009. 〕 The word "autapomorphy" is derived from the Greek words ''αὐτός'', ''aut'' = self; ''ἀπό'', ''apo'' = away from; and ''μορφή'', ''morphe'' = shape. An autapomorphy is not present in the closest relative of the terminal group and also was not present in their common ancestor. An example of an autapomorphy can be described in modern snakes. Snakes have lost the two pairs of legs that characterize all of Tetrapoda, and the closest taxa to Ophidia - as well as their common ancestors - all have two pairs of legs. Therefore, the Ophidia taxon presents an autapomorphy with respect to its absence of legs.〔 The words ''autapomorphy'' and ''synapomorphy'' technically describe the same derived character-state, but they differ in context: Synapomorphy describes the trait as it typifies the taxon and contrasts it with a different condition in outgroups, while autapomorphy should be correctly used when the component taxa are not mentioned.〔Carpenter, Kenneth and Currie, Philip J. ''Dinosaur Systematics: Approaches and Perspectives.'' Cambridge University Press, 1992. Page 134.〕 An autapomorphy at a given taxonomic level may therefore also be a synapomorphy at a less-inclusive level.〔Forey, Peter L. ''History of the Coelacanth Fishes.'' Sprinter, 1st edition. 1997.〕 The ''autapomorphic species concept'' is one of many methods that scientists might use to define and distinguish species from one another. This definition assigns species on the basis of amount of divergence associated with reproductive incompatibility, which is measured essentially by number of autapomorphies.〔Howard, Daniel J.; Berlocher, Stewart H. ''Endless Forms: Species and Speciation.'' Oxford University Press, USA; 1st edition. 1998.〕 This grouping method is often referred to as the "monophyletic species concept" or the "phylospecies" concept and was popularized by D.E. Rosen in 1979. Within this definition, a species is seen as "the least inclusive monophyletic group definable by at least one autapomorphy."〔Bull, Alan T. ''Microbial Diversity and Bioprospecting.'' ASM Press, 2004.〕 While this model of speciation is useful in that it avoids non-monophyletic groupings, it has its criticisms as well. N.I. Platnick, for example, believes the autapomorphic species concept to be inadequate because it allows for the possibility of reproductive isolation and speciation while revoking the "species" status of the mother population. In other words, if a peripheral population breaks away and becomes reproductively isolated, it would conceivably need to develop at least one autapomorphy to be recognized as a different species. If this can happen without the larger mother population ''also'' developing a new autapomorphy, then the mother population cannot remain a species under the autapomorphic species concept: it would no longer have any apomorphies not also shared by the daughter species. The term "autapomorphy" was first introduced in 1950 by German entomologist Willi Hennig, who is widely regarded as the father of modern cladistics.〔 ==See also== * Homoplasy – a trait that is found in several terminal groups but evolved independently (i.e., was not present in their common ancestor) * Synapomorphy – a trait that is found in some or all terminal groups of a clade, and inherited from a common ancestor, for which it was an autapomorphy (i.e., not present in ''its'' immediate ancestor). * * ''Underlying synapomorphy'' – a synapomorphy that has been lost again in many members of the clade. If lost in all but one, it can be hard to distinguish from an autapomorphy. * * ''Apomorphy'' – the underlying character state in question, whether unique to a single taxon (autapomorphic) or shared between taxa (synapomorphic). * Symplesiomorphy – an ancestral trait shared by two or more taxa. * * ''Plesiomorphy'' – a symplesiomorphy discussed in reference to a more derived state. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「autapomorphy」の詳細全文を読む スポンサード リンク
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