Figure 2.

The potential role of inherited epigenetic changes, comparing the effects of spontaneous and induced epimutations. A population of genotypically identical individuals is shown, which contain a single locus that can exist in two epigenetic states. Like spontaneous epimutations, induced epimutations are maintained across generations, but revert randomly without the inducing environment (which almost never happens for DNA mutations). The epiallele marked in purple is disadvantageous in a normal environment (leading to increased death; red crosses). In a stress environment (indicated by a thunder bolt), the unmodified allele (shown in grey) is disadvantageous. If the environment changes randomly from generation to generation, induced epivariation is unlikely to be advantageous. If there are longer episodes of stress, induced epivariation could be advantageous, and Darwinian selection might favor alleles that can become subject to induced epivariation. However, formalization is needed to determine the boundary conditions for such a scenario.