Increased fluctuating asymmetry (FA) of morphological traits occurs under environmental and genomic stress. Such conditions will therefore lead to a reduction in developmental homeostasis. Based upon temperature extreme experiments, relatively severe stress is needed to increase FA under field conditions. Increasing asymmetry tends, therefore, to occur in stressed marginal habitats. Genetic perturbations implying genomic stress include certain specific genes, directional selection, inbreeding, and chromosome balance alterations. It is for these reasons that transgenic organisms may show increased FA. As there is evidence that the effects of genomic and environmental stress are cumulative, organisms in a state of genomic stress may provide sensitive biological monitors of environmental stress.