“…Indeed, when there are too many men, the nature of relationships change. For example, Angrist found that, among immigrants to the USA, high sex ratios had a large positive effect on the likelihood of female marriage and a large negative effect on female labor force participation; with men providing investment, women could avoid wage labor [37]. In general, malebiased sex ratios are associated with a greater proportion of males being married [34,38], less promiscuity in both sexes [36,39,40], and greater conjugal stability [41], all of which might contribute to the lower I s values for men shown in Box 2.…”