Abstract
A stable population theory is constructed where income, rather than age, takes the dominant role in the dynamics. The model's structure is based on a Becker (1960) and Willis (1973) household-utility-maximizing assumption where both the desired number of children and the optimal per-child bequest are endogenously determined. Yet, the stable population results still will apply even if the utility-maximizing hypothesis is dropped. Under weak assumptions about individual preferences and household structure, the existence of a unique stationary state which implies both a constant population growth and a stationary income distribution is formed. These 2 facts form an income-specific stable population theory that differs from Lotka's age-spectific stable population theory. It is shown that classifying people on the basis of their incomes is a promising alternative to classifying people on the basis of their ages. Theoretically, the paper extends the Becker-Willis micro-level, static fertility demand model to a macro-level, dynamic population growth structure. Empirically, it is demonstrated that the model can be applied to analyzing the relations between income distribution and population growth, average savings rate and population growth, and long-run population projections.