Figure 1.

The curves labeled b_1s = 0 and b_1s = 1 give the minimum values of the inbreeding depression, d, for which the two norms of reaction b_1r = b_1s = 0 and b_1r = 0 with b_1s = 1 will be evolutionarily stable against all alternatives that satisfy b_2r > 0. The horizontal axis measures the probability, h, that an incestuous female mates with an unrelated male when her brother dies. For intermediate values of b_1s, there is a family of nonintersecting curves that lie between these two curves. The curve labeled b_1s = 0 meets the d axis at 1/3.