Fig. 1.
The conceptual framework shared by two hypotheses for the evolution of selfing. Selfing will evolve by its gene-level transmission advantage if it is not erased by pollen discounting (px – ps) or inbreeding depression (δ). If selfing increases seed production, selfing will be selected if the number of alleles passed on by plants capable of selfing (2y + xs + ps) is greater than the number transmitted by outcrossers (xx + px), and exceeds a threshold inbreeding depression. Pollen and seed discounting (xx – xs) may both counter selection of selfing in this case.