Considerable attention has been paid to estimating genetic variability in quantitative traits and to how it is maintained and changed by selection in natural and domesticated populations, but rather little attention has been paid to how levels of environmental and phenotypic variance are influenced. We review recent estimates, showing there is substantial genetic variation in levels of environmental and phenotypic variation. We review evolutionary forces that can affect the level of environmental variation, and find that most models lead to a predicted reduction. We thus argue that its maintenance is a consequence of factors such as the intrinsic cost of homogeneity, phenotypic plasticity to variable environments, or mutants that increase variance. We show how to construct a selection index to predict the magnitude of changes in variance as a result of artificial selection, and consider the opportunities for artificial selection to increase uniformity
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