Developmental theory is based on the assumption that traditional societies are characterized by sharply differentiated gender roles that discourage women from working outside the home. An extensive literature in demography, sociology, anthropology, and social psychology has documented the familiar yet profound transformation of sex roles associated with the process of societal modernization. Virtually all preindustrial societies emphasize childbearing and child rearing as the central goal for women and their most important function in life, along with tasks like food production and preparation at home; jobs in the paid workforce are predominately male. In postindustrial societies, gender roles have increasingly converged because of a structural revolution in the paid labor force, in educational opportunities for women, and in the characteristics of modern families. In most affluent countries, people are marrying later than in previous generations and having fewer children. A rapid increase in premarital cohabitation is challenging the once-privileged position held by marriage. More and more women, especially those who are married, have entered the paid labor force, creating the transition from male breadwinner to dual-earning families. Although the gender gap in rates of economic participation is narrowing, women's and men's roles in the labor force continue to differ. Women still have to juggle the demands of family responsibilities and market work, and they hold different jobs than men do, often with lower status and rewards.