ABSTRACT
This chapter discusses two theoretical models of population in which the link between the patterns of fertility and mortality, on the one hand, and the structure of the population, on the other, is made completely explicit. The manner in which birth cohorts progressively disappear under the impact of mortality leads to a first theoretical population model. In stationary populations, ageing is often the more marked the higher the expectation of life. The model of the stationary population resulted from the action of a life table upon a fixed annual number of births. Stable populations are richer and more variable models that stationary populations, since a given life table can be associated with an infinite number of stable populations, each one individualized by the given rate of natural increases.
