The 1960s changed premarital sex. Prior to the sexual revolution, unmarried heterosexual sex partners tended to marry each other (sometimes motivated by a shotgun pregnancy); in more recent decades, first sex usually does not lead to marriage. Figure 1 shows how the odds of having only one lifetime sex partner have declined over the 20thcentury for married Americans. The biggest declines occurred for people born between the 1920s and the 1940s, the latter of whom came of age during the sexual...
