Figure 2: Synergy model.
From: Coevolution of parental investment and sexually selected traits drives sex-role divergence
If the sexes differ only in their initial amount of care (a), equal care by both sexes evolves. Any deviation from 
and 
shifts the stable proportion of care towards the sex which faces stronger sexual selection (b), lower parentage certainty (c) or both, leading to unisexual care if the asymmetry is large enough (d). Parameter values: k=n=M=r=1; 
; α=γ=0.1.
