Fig. 1. Model of parental investment from behind a veil of ignorance.

A Zones of agreement and disagreement over which mother cares for which offspring (see main text), when b(x) = x(1 − x/2) (for x ≤ 1) and c(k;y) = k y². Two illustrative sets of parameter values are marked: point A (in the zone of disagreement) where we assume that initial asymmetries between parents and between offspring are smaller (k₁ = 1.25, k₂ = 0.75, x_hi = 0.25, x_lo = 0.15) and point B (in the zone of agreement) where initial asymmetries between parents and between offspring are larger (k₁ = 1.5, k₂ = 0.5, x_hi = 0.3, x_lo = 0.1). B The predicted prenatal (purple shading) and postnatal (light blue shading) investment received by each offspring given each of the two sets of parameter values A and B. For each set of parameter values A and B we show the outcomes when (i) the inferior carer, here mother 1, looks after the initially smaller offspring (outcomes A1 and B1), and when (ii) mother 1 looks after the initially larger offspring (outcomes A2 and B2). At point A, the mothers disagree over who should care for whom, so neither outcome is universally preferred; at point B, outcome B2 is preferred by both parents, so outcome B1 is never chosen and is crossed out. C Variance in offspring size before and after postnatal investment at point A, assuming either outcome A1 (solid red line) or that outcomes A1 and A2 are equally probable (dashed red line), and at point B, assuming the mutually preferred outcome B2 (solid blue line).