Editing Punctuated equilibrium (section)

===Punctuational change===

When Eldredge and Gould published their 1972 paper, [[allopatric speciation]] was considered the "standard" model of speciation.<ref name=pe1972 /> This model was popularized by Ernst Mayr in his 1954 paper "Change of genetic environment and evolution,"<ref name=Mayr1954 /> and his classic volume ''Animal Species and Evolution'' (1963).<ref name="Mayr1963">[[Ernst Mayr|Mayr, Ernst]] (1963). ''Animal Species and Evolution''. Cambridge, MA: [[Harvard University Press]].</ref>

Allopatric speciation suggests that species with large central populations are stabilized by their large volume and the process of [[gene flow]]. New and even [[Mutation#Beneficial mutations|beneficial mutations]] are diluted by the population's large size and are unable to reach fixation, due to such factors as constantly changing environments.<ref name="Mayr1963" /> If this is the case, then the transformation of whole lineages should be rare, as the fossil record indicates. Smaller populations on the other hand, which are isolated from the parental stock, are decoupled from the [[wikt:Homogeneous|homogenizing]] effects of gene flow. In addition, pressure from [[natural selection]] is especially intense, as peripheral isolated populations exist at the outer edges of [[ecological tolerance]]. If most evolution happens in these rare instances of allopatric speciation then evidence of gradual evolution in the fossil record should be rare. This [[hypothesis]] was alluded to by Mayr in the closing paragraph of his 1954 paper:

{{Blockquote|Rapidly evolving peripherally isolated populations may be the place of origin of many evolutionary novelties. Their isolation and comparatively small size may explain phenomena of rapid evolution and lack of documentation in the fossil record, hitherto puzzling to the palaeontologist.<ref name=Mayr1954 />}}

Although punctuated equilibrium generally applies to sexually reproducing organisms,<ref>[[Niles Eldredge|Eldredge, Niles]] and [[Stephen Jay Gould|S. J. Gould]] (1997). [http://www.stephenjaygould.org/library/science_on-punctuated-equilibria.html "On punctuated equilibria (letter)."] ''Science'' 276 (5311): 337-341.</ref> some biologists have applied the model to non-sexual species like [[virus]]es,<ref>Nichol, S.T, Joan Rowe, and Walter M. Fitch (1993). [http://www.pnas.org/content/90/22/10424.full.pdf "Punctuated equilibrium and positive Darwinian evolution in vesicular stomatitis virus."] ''Proceedings of the National Academy of Sciences'' 90 (Nov.): 10424-28.</ref><ref>Elena S.F., V.S. Cooper, and R. Lenski (1996). [https://web.archive.org/web/20030514101700/http://myxo.css.msu.edu/lenski/pdf/1996,%20Science,%20Elena%20et%20al.pdf "Punctuated Evolution Caused by Selection of Rare Beneficial Mutations."] ''Science'' 272 (June 21): 1802-1804.</ref> which cannot be stabilized by conventional gene flow. As time went on biologists like Gould moved away from wedding punctuated equilibrium to allopatric speciation, particularly as evidence accumulated in support of other modes of speciation.<ref name="GouldNewScientist"/> Gould, for example, was particularly attracted to [[Douglas J. Futuyma|Douglas Futuyma's]] work on the importance of reproductive isolating mechanisms.<ref>{{cite journal |last=Futuyma |first=Douglas |date=1987 |title=On the role of species in anagenesis |journal=[[The American Naturalist|American Naturalist]] |doi=10.1086/284724 |volume=130 |issue=3 |pages=465–473|bibcode=1987ANat..130..465F |s2cid=83546424 }}</ref>