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. 2018 Jun 2;5:101–113. doi: 10.1016/j.ssmph.2018.05.010

Fig. 1.

Fig. 1

Schematic illustration of fetal needs and maternal capacity to invest. TOP PANEL: X-axis describes Darwinian fitness. Y-axis on the left (orange) indicates level of resource need for fetuses F, which varies across pregnancies. Needs of fetuses F1 decline with increased fitness. Y-axis on the right (blue dash) indicates maternal capacity to invest in children M1; maternal capacity varies positively with maternal fitness. Selection in utero occurs when F1 > M1. Vertical dashed line indicates point at which F1 = M1. BOTTOM PANEL: To the left of this dashed line, the “left tail” of the frequency distribution of fetuses (shaded) undergoes selection in utero. Theory suggests that fewer high need infants will be born when the environment weakens women of reproductive age (i.e., down-shift of M1 to M2 while F1 remains fixed). Selection in utero, moreover, would increase when maternal resources remain fixed but needs of the fetus shift upward (i.e., F1 to F2, with M1 fixed). Perturbations of maternal capacity and fetal need may also occur simultaneously and interact according to parental-offspring conflict theory (Haig, 1993).