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Punctuated equilibrium (also called punctuated equilibria) is a theory in evolutionary biology which proposes that once species appear in the fossil record they will become stable, showing little net evolutionary change for most of their geological history. This state is called ''stasis''. When significant evolutionary change occurs, the theory proposes that it is generally restricted to rare and geologically rapid events of branching speciation called cladogenesis. Cladogenesis is the process by which a species splits into two distinct species, rather than one species gradually transforming into another.〔Gould, Stephen Jay, & Eldredge, Niles (1977). ("Punctuated equilibria: the tempo and mode of evolution reconsidered." ) ''Paleobiology'' 3 (2): 115-151. (p.145)〕 Punctuated equilibrium is commonly contrasted against phyletic gradualism, the belief that evolution generally occurs uniformly and by the steady and gradual transformation of whole lineages (called anagenesis). In this view, evolution is seen as generally smooth and continuous. In 1972, paleontologists Niles Eldredge and Stephen Jay Gould published a landmark paper developing their theory and called it ''punctuated equilibria''.〔Eldredge, Niles and S. J. Gould (1972). ("Punctuated equilibria: an alternative to phyletic gradualism" ) In T.J.M. Schopf, ed., ''Models in Paleobiology''. San Francisco: Freeman Cooper. pp. 82-115. Reprinted in N. Eldredge ''Time frames''. Princeton: Princeton Univ. Press, 1985, (pp. 193-223 ).〕 Their paper built upon Ernst Mayr's model of geographic speciation,〔Mayr, Ernst (1954). ("Change of genetic environment and evolution" ) In J. Huxley, A. C. Hardy and E. B. Ford. ''Evolution as a Process''. London: Allen and Unwin, pp. 157-180.〕 I. Michael Lerner's theories of developmental and genetic homeostasis,〔Lerner, Israel Michael (1954). ''Genetic Homeostasis''. New York: John Wiley.〕 as well as their own empirical research. Eldredge and Gould proposed that the degree of gradualism commonly attributed to Charles Darwin is virtually nonexistent in the fossil record, and that stasis dominates the history of most fossil species. ==History== Punctuated equilibrium originated as a logical extension of Ernst Mayr's concept of genetic revolutions by allopatric and especially peripatric speciation as applied to the fossil record. Although some of the basic workings of the theory were proposed and identified by Mayr in 1954,〔 historians of science generally recognize the 1972 paper by Niles Eldredge and Stephen Jay Gould as the foundation of the new paleobiological research program.〔Mayr, Ernst (1992). ("Speciational Evolution or Punctuated Equilibria." ) In Albert Somit and Steven Peterson ''The Dynamics of Evolution''. New York: Cornell University Press, pp. 21-48.〕〔Shermer, Michael (2001). ''The Borderlands of Science''. New York: Oxford University Press.〕〔Geary, Dana (2008). ("The Legacy of Punctuated equilibrium." ) In Warren D. Allmon et al. ''Stephen Jay Gould: Reflections on His View of Life''. Oxford: Oxford University Press, pp. 127-145.〕 Punctuated equilibrium differs from Mayr's theory mainly in that Eldredge and Gould placed considerably greater emphasis on stasis, whereas Mayr was generally concerned with explaining the morphological discontinuity (or "sudden jumps")〔Schindewolf, Otto (1936). ''Paldontologie, Entwicklungslehre und Genetik''. Berlin: Borntraeger.〕 found in the fossil record.〔 Mayr later complimented Eldredge and Gould's paper, stating that evolutionary stasis had been "unexpected by most evolutionary biologists" and that punctuated equilibrium "had a major impact on paleontology and evolutionary biology".〔 A year before their 1972 Eldredge and Gould paper, Niles Eldredge published a paper in the journal ''Evolution'' which suggested that gradual evolution was seldom seen in the fossil record and argued that Ernst Mayr's standard mechanism of allopatric speciation might suggest a possible resolution.〔 The Eldredge and Gould paper was presented at the Annual Meeting of the Geological Society of America in 1971.〔 The symposium focused its attention on the possibility that modern microevolutionary studies could revitalize various aspects of paleontology and macroevolution. Tom Schopf, who organized that year's meeting, assigned Gould the topic of speciation. Gould recalls that "Eldredge's 1971 publication (Paleozoic trilobites ) had presented the only new and interesting ideas on the paleontological implications of the subject—so I asked Schopf if we could present the paper jointly." According to Gould "the ideas came mostly from Niles, with yours truly acting as a sounding board and eventual scribe. I coined the term ''punctuated equilibrium'' and wrote most of our 1972 paper, but Niles is the proper first author in our pairing of Eldredge and Gould."〔Gould, S. J. (1991). ("Opus 200" ) ''Natural History'' 100 (August): 12-18.〕 In his book ''Time Frames'' Eldredge recalls that after much discussion the pair "each wrote roughly half. Some of the parts that would seem obviously the work of one of us were actually first penned by the other—I remember for example, writing the section on Gould's snails. Other parts are harder to reconstruct. Gould edited the entire manuscript for better consistency. We sent it in, and Schopf reacted strongly against it—thus signaling the tenor of the reaction it has engendered, though for shifting reasons, down to the present day."〔Eldredge, N. 1985. ''Time Frames: The evolution of punctuated equilibria''. Princeton: Princeton University Press, p. 120.〕 John Wilkins and Gareth Nelson have argued that French architect Pierre Trémaux proposed an "anticipation of the theory of punctuated equilibrium of Gould and Eldredge."〔Wilkins, John S. and G.J. Nelson (2008). ("Trémaux on species: A theory of allopatric speciation (and punctuated equilibrium) before Wagner." ) ''History and Philosophy of the Life Sciences'' 30: 179-206.〕 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「Punctuated equilibrium」の詳細全文を読む スポンサード リンク
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