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Genic and Organismic Selection

Sewall Wright
Evolution
Vol. 34, No. 5 (Sep., 1980), pp. 825-843
DOI: 10.2307/2407990
Stable URL: http://www.jstor.org/stable/2407990
Page Count: 19
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Genic and Organismic Selection
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Abstract

In a panmictic population, natural selection operates on the field of variability provided by mutation merely according to the average effects of allelic differences in all combinations. It is a creative process but one severely limited by the complexity of the relations between primary gene action and the characters involved directly in the fitness of individuals, a complexity that insures that each allelic difference has pleiotropic effects. Creativity is raised to the second power, however, if the field of variability is amplified by random differentiation among numerous partially isolated local populations, and selection is amplified by selective diffusion from those local populations that happen to have acquired superior coadaptive systems of genes by shifts to control by superior peaks in the adaptive topography. Theoretical studies indicate the probable occurrence in most species of population structures favorable to sufficient random drift to permit the occurrence of peak-shifts. The evidence from studies of species in nature, however, needs to be greatly extended since at present the data are somewhat ambiguous because of the difficulty that apparent random differentiation may be due to unrecognized differences in the conditions of selection. The data are, however, at least consistent with an important role of the shifting balance process in evolution. The likelihood of organismic, instead of merely genic, selection goes far toward meeting one of the most serious objections to the theory of natural selection encountered by Darwin.

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