Although spontaneous rates of genetic mutations are well understood, the rates of epigenetic variation in DNA methylation have remained a mystery until now. Using the plant Arabidopsis thaliana (depicted in the center), generational variation in DNA methylation was identified in five lineages separated by 30 generations of growth as indicated by the methylated pink Cs and the unmethylated green Cs. Image Credit: Concept/artwork/ image design: Robert Schmitz, Joseph R. Ecker, Salk Institute for Biological Studies