The article focuses on the economics of family partnerships. It states an allegory involving a prehistoric couple who split their responsibilities of gathering food and building a fire to create econometric models for family behavior. In theory, monogamous couples have exactly the same interest in their reproductive success, hence completely shared interest in their children. This is not the case in practice, as a variety of marital problems, divorce, and remarriage adversely affect the equation. The observed fact that an increase in a society's wealth tends to decrease family size runs counter to evolutionary biologic theory. No one theory in economics or biology has an adequate explanation for the reduction in family size as wealth increases. A variety of outside factors, notably the decline in child mortality and the change from an agricultural to an urban society, affect the models in both disciplines.