Editing Quantum evolution (section)

==Mechanisms==
According to Simpson (1944), quantum evolution resulted from [[Sewall Wright]]'s model of [[genetic drift|random genetic drift]]. Simpson believed that major evolutionary transitions would arise when small populations, that were [[Allopatric speciation|isolated]] and limited from [[gene flow]], would fixate upon unusual gene combinations. This "inadaptive phase" (caused by genetic drift) would then (by natural selection) drive a [[deme (biology)|deme population]] from one stable adaptive peak to another on the [[fitness landscape|adaptive fitness landscape]]. However, in his ''Major Features of Evolution'' (1953) Simpson wrote that this mechanism was still controversial:

<Blockquote>"whether prospective adaptation as prelude to quantum evolution arises adaptively or inadaptively. It was concluded above that it usually arises adaptively . . . . The precise role of, say, genetic drift in this process thus is largely speculative at present. It may have an essential part or none. It surely is not involved in all cases of quantum evolution, but there is a strong possibility that it is often involved. If or when it is involved, it is an initiating mechanism. Drift can only rarely, and only for lower categories, have completed the transition to a new adaptive zone."<ref>Simpson, G. G. (1953). ''[http://www.stephenjaygould.org/library/simpson_evolutionary-rates.html The Major Features of Evolution]'', p. 390.</ref></Blockquote>

This preference for adaptive over inadaptive forces led [[Stephen Jay Gould]] to call attention to the "hardening of the Modern Synthesis", a trend in the 1950s where adaptationism took precedence over the pluralism of mechanisms common in the 1930s and 40s.<ref>Gould, S. J. (1983). [http://www.stephenjaygould.org/library/gould_synthesis.html "The hardening of the Modern Synthesis"] In Marjorie Grene, ed., ''Dimensions of Darwinism''. Cambridge UK: Cambridge University Press, pp. 71-93.</ref>

Simpson considered quantum evolution his crowning achievement, being "perhaps the most important outcome of [my] investigation, but also the most controversial and hypothetical."<ref name="Simpson1944p206"/>