Secular change in sex ratios is examined in relation to experience in the family. Two theoretical perspectives are outlined: Guttentag and Secord’s (1983) adaptation of social exchange theory, and sexual selection theory. Because of large-scale change in number of births and typical age differentials between men and women at marriage, low sex ratios at couple formation ages existed in the U.S. between 1965 and the early 1980s. The currently high sex ratios, however, will persist until the end of the century. (...) High sex ratios appear to be associated with lower divorce rates, male commitment to careers that promise economic rewards, male willingness to engage in child care, higher fertility, and higher rates of sexual violence. Sexual selection theory calls attention to intrasexual competition in the numerically larger sex. (shrink)