et al.54 have served as groundbreakers, discovering that, with respect to intelligence, children carrying one variant of FADS2, a gene involved in the genetic control of fatty acid pathways, benefit from breastfeeding, whereas those carrying a different allele are not so affected. What has not been determined as of yet, because all mothers in this study were apparently in relatively good nutritional state, is whether those individuals found to benefit from breastfeeding for genetic reasons actually are adversely affected by it when mothers are in poor nutritional condition. Not only is this just what a differential-susceptibility perspective would predict, but is also what might explain why the gene associated with increased intelligence in the context of breastfeeding, most certainly the universal condition in ancestral times, has not gone to fixation.
