Fig. 6.

Results of simulations demonstrating that increased stochastic variation in the epigenome would increase fitness in a varying environment. (A) Simulations of natural selection. For each simulation, we computed the population average and SD of the phenotype as a function of generation. Two simulations are shown: simulation 1, natural selection in a fixed environment favoring positive Y but including a novel stochastic epigenetic element, such that eight mutations affect average Y and eight mutations affect variance of Y, and simulation 2, similar to simulation 1 but in this case allowing a changing environment across generations that favor at times positive Y and at times negative Y. The top panel shows the average (across all iterations) population average of Y as a function of generation for simulation 1 (green) and simulation 2 (orange). The dashed vertical lines indicate the generations at which the environment was changed in simulation 2. The bottom panel shows the average (across all iterations) population standard deviation of Y. Note that with a changing environment, the average Y fluctuates around a common point, but the SD of Y increases consistently. (B) Emulation of GWAS analysis based on simulation 2 (varying variance of Y). Observed odds ratios are for SNPs that change the mean phenotype.