It may also become a factor in societal and demographic collapse. For example, the native population of Cusco, Peru at the time of the Spanish conquest was stressed by an imbalance in the sex ratio between men and women.[68] Analyses of how sex ratio imbalances affect personal consumption and intra-household distribution were pioneered by Gary Becker, Shoshana Grossbard-Shechtman,[69][70] and Marcia Guttentag and Paul Secord.[71] High ratios of males have a positive effect on marital fertility and women's share of household consumption and negative effects on non-marital cohabitation and fertility and women's labor supply. It has been shown that variation in sex ratio over time is inversely related to married women's labor supply in the U.S.[72][73]