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In biology, saltation (from Latin, ''saltus'', "leap") is a sudden change from one generation to the next, that is large, or very large, in comparison with the usual variation of an organism. The term is used for nongradual changes (especially single-step speciation) that are atypical of, or violate, gradualism—involved in modern evolutionary theory. ==History== Prior to Charles Darwin most evolutionary scientists had been saltationists.〔Henry Fairfield Osborn. (1894). ''From the Greeks to Darwin: An outline of the development of the evolution idea''. New York, London, Macmillan and Co.〕 Jean-Baptiste Lamarck was a gradualist but similar to other scientists of the period had written that saltational evolution was possible. Étienne Geoffroy Saint-Hilaire endorsed a theory of saltational evolution that "monstrosities could become the founding fathers (or mothers) of new species by instantaneous transition from one form to the next."〔Benedikt Hallgrímsson, Brian K. Hall. (2011). ''Variation: A Central Concept in Biology''. Academic Press. p. 18〕 Geoffroy wrote that environmental pressures could produce sudden transformations to establish new species instantaneously.〔Peter J. Bowler. (2003). ''Evolution: The History of an Idea''. University of California Press. p. 127〕 In 1864 Albert von Kölliker revived Geoffroy's theory that evolution proceeds by large steps, under the name of heterogenesis.〔Sewall Wright. (1984). ''Evolution and the Genetics of Populations: Genetics and Biometric Foundations Volume 1''. University of Chicago Press. p. 10〕 With the publication of ''On the Origin of Species'' in 1859 Charles Darwin had denied saltational evolution by writing that evolutionary transformation always proceeds gradually and never in jumps. Darwin insisted on slow accumulation of small steps in evolution and wrote "natural selection acts solely by accumulating slight successive favourable variations, it can produce no great or sudden modification; it can act only by very short steps". Darwin continued in this belief throughout his life. 〔Charles Darwin. (1859). ''On the Origin of Species''. p. 471〕 From 1860 to 1880 saltation had a minority interest but by 1890 had become a major interest to scientists.〔Gregory Radick. (2008). ''The Simian Tongue: The Long Debate about Animal Language''. University Of Chicago Press. p. 368〕 In their paper on evolutionary theories in the 20th century (Levit ''et al''. 2008) wrote: The advocates of saltationism deny the Darwinian idea of slowly and gradually growing divergence of character as the only source of evolutionary progress. They would not necessarily completely deny gradual variation, but claim that cardinally new ‘body plans’ come into being as a result of saltations (sudden, discontinuous and crucial changes, for example, the series of macromutations). The latter are responsible for the sudden appearance of new higher taxa including classes and orders, while small variation is supposed to be responsible for the fine adaptations below the species level.〔Levit, G. S, Meister, K. Hoßfeld, U. (2008). ''Alternative Evolutionary Theories: A Historical Survey''. Journal of Bioeconomics 10.1. pp. 71–96.〕 In the early 20th century a mechanism of saltation was proposed as large mutations. It was seen as a much faster alternative to the Darwinian concept of a gradual process of small random variations being acted on by natural selection. It was popular with early geneticists such as Hugo de Vries, who along with Carl Correns helped rediscover Gregor Mendel's laws of inheritance in 1900, William Bateson, a British zoologist who switched to genetics, and early in his career Thomas Hunt Morgan. Some of these geneticists developed it into the mutation theory of evolution. There was also a debate over accounts of the evolution of mimicry and if they could be explained by gradualism or saltation. The geneticist Reginald Punnett supported a saltational theory in his book ''Mimicry in Butterflies'' (1915).〔Reginald Punnett. (1915). (''Mimicry in Butterflies'' ). Cornell University Library.〕 The mutation theory of evolution held that species went through periods of rapid mutation, possibly as a result of environmental stress, that could produce multiple mutations, and in some cases completely new species, in a single generation. This mutationist view of evolution was later replaced by the reconciliation of Mendelian genetics with natural selection into a gradualistic framework for the neo-Darwinian synthesis.〔Peter J. Bowler. (2003). ''Evolution: The History of an Idea''. University of California Press.〕 It was the emergence of population thinking in evolution which forced many scientists to adopt gradualism in the early 20th century. According to Ernst Mayr, it wasn't until the development of population genetics in the neo-Darwinian synthesis in the 1940s that demonstrated the explanatory power of natural selection that saltational views of evolution were largely abandoned.〔Ernst Mayr. (2007). ''What Makes Biology Unique?: Considerations on the Autonomy of a Scientific Discipline''. Cambridge University Press; 1 edition〕 Saltation was originally denied by the "modern synthesis" school of neo-Darwinism which favoured gradual evolution but has since been accepted due to recent evidence in evolutionary biology (see the current status section).〔Bateman, R. M. and DiMichele, W. A. (1994). ''Saltational evolution of form in vascular plants: a neoGoldschmidtian synthesis''. In ''Shape and Form in Plants and Fungi'' (eds D. S. Ingram and A. Hudson), Academic Press, London. pp. 61-100.〕〔Gregory, T. R. and Hebert, P. D. N. (1999). (''The modulation of DNA content: proximate causes and ultimate consequences'' ). Genome Res. 9, 317–324.〕〔Eva Jablonka and Marion J. Lamb. (2005). ''Evolution in Four Dimensions: Genetic, Epigenetic, Behavioral, and Symbolic Variation in the History of Life''. A Bradford Book. ISBN 0262600692〕〔Serres MH, Kerr AR, McCormack TJ, Riley M. (2009). (''Evolution by leaps: gene duplication in bacteria'' ). Biology Direct 4: 46.〕 In recent years there are some prominent proponents of saltation, including Carl Woese. Woese, and colleagues, suggested that the absence of RNA signature continuum between domains of bacteria, archaea, and eukarya constitutes a primary indication that the three primary organismal lineages materialized via one or more major evolutionary saltations from some universal ancestral state involving dramatic change in cellular organization that was significant early in the evolution of life, but in complex organisms gave way to the generally accepted Darwinian mechanisms.〔Roberts, E., A. Sethi, J. Montoya, C.R. Woese and Z. Luthey-Schulten. (2008). (''Molecular signatures of ribosomal evolution'' ). Proc. Natl. Acad. Sci. USA, 105: 13953–13958.〕 The geneticist Barbara McClintock introduced the idea of "jumping genes", chromosome transpositions that can produce rapid changes in the genome.〔McClintock, B. (1984). ''The significance of responses of the genome to challenge''. Science Vol. 226, pp. 792-801.〕 Saltational speciation, also known as abrupt speciation, is the discontinuity in a lineage that occurs through genetic mutations, chromosomal aberrations or other evolutionary mechanisms that cause reproductively isolated individuals to establish a new species population. Polyploidy, karyotypic fission, symbiogenesis and lateral gene transfer are possible mechanisms for saltational speciation.〔Oladele Ogunseitan. (2004). ''Microbial Diversity: Form and Function in Prokaryotes''. Wiley-Blackwell. p. 13. ISBN 978-0632047086〕 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「Saltation (biology)」の詳細全文を読む スポンサード リンク
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