Constant global population with demographic heterogeneity

Joel E. Cohen, Rockefeller University and Columbia University

To understand better a possible future constant global population that is demographically heterogeneous, this paper analyzes several models. Classical theory of stationary populations generally fails to apply. However, if constant global population size P (global) is the sum of all country population sizes, and if constant global annual number of births B (global) is the sum of the annual number of births of all countries, and if constant global life expectancy at birth e(global) is the population-weighted mean of the life expectancy at birth of all countries, then B(global) · e(global) always exceeds P(global) unless all countries have the same life expectancy at birth, in which case B(global) · e(global) = P(global).