“…Such differences, in turn, might lead to competition, disparities, and conflicts that might affect cognitive development (Downey 2001;Downey, Condron, and Yucel 2015). This compounding effect extends through the life course, with early cognitive development acting as a foundation upon which future educational achievements, career opportunities, and social capital are built (Barclay, Lyngstad, and Conley 2018;Downey et al 2015). The extent of resource dilution might differ by siblings' sex composition with sister-sister siblings share more emotional and instrumental support than brothers (Buist, Deković, and Prinzie 2013;Feinberg, Solmeyer, and McHale 2012).…”