| Abstract: | Having argued that phenotypic variation with respect to the component of fitness involved in withstanding density stress is useful for the persistence of populations through time, the sources of such variation are described. Age differences and differences caused by the accidental encounters of dissimilar microenvironments are non-genetic in origin. Genetic bases for phenotypic variation can either be proximate (each individual having a unique genotype) or ultimate. The latter case is one in which the genotypes of individuals are such that the progeny they produce are phenotypically variable. Selection favouring such genotypes can be shown to be Darwinian; group selection is not required. A means for revealing instances of the ultimate genetic control of phenotypic variation is suggested: measures of what should be error variance prove to be larger than those which should, under normal circumstances, include error variance. The last increment of variation that causes what might otherwise be repetitive structures to differ can be ascribed to decisions that are genetically pre-set within developmental programmes. |
