The degree to which people experience threats to their survival shapes their basic values. Throughout history, most people lived just above the starvation level, but in the years after World War II, unprecedented prosperity and social welfare safety nets launched an intergenerational shift from survival to self-expression values. When the first postwar birth cohort reached adulthood in the 1960s, student protests erupted, inaugurating pervasive cultural changes. Historically, a coherent set of pro-fertility norms evolved that limits women to producing as many children as possible and that stigmatizes any other form of sexual behavior not linked with reproduction. Because pro-fertility norms require people to repress strong drives, there is a built-in tension between them and their polar opposite, individual-choice norms. Throughout history, societies that lacked pro-fertility norms tended to die out, but in recent decades, a growing number of societies have attained high existential security, long life expectancy, and low infant mortality, opening the way for a shift from pro-fertility norms to individual-choice norms.