This line of argument emphasizes that the breadwinner-housekeeper division of labor within a marital union creates “gains to trade”, and thus marriage is a rational choice for two individuals who wish to build a joint economic unit that maximizes productivity. It follows that the gains from marriage are largely reduced when women gain more ground in higher education and the labor market and become less dependent on their spouses‟ income. In turn, the opportunity costs of marriage increase, so that gainfully employed women tend to have a lower incentive to establish a family, and less time for childrearing and domestic work.