Figure 1.
Predicted effect of extrinsic risk on offspring fitness as a function of parental effort. Note: adapted from Pennington & Harpending (1988). Smax (saturation point of parental effort) is a function of extrinsic risk. Smax is the point at which additional parental effort does not improve offspring fitness (i.e. the point at which the derivative of the offspring fitness function equals zero).