Chapter 5. Population Poverty and the Natural Environment This chapter studies the interface in poor countries of population growth rural poverty and deterioration of the local natural resource base a subject that has been much neglected by modern demographers and development economists. The motivations for procreation in rural communities of the poorest regions of the world are analyzed and recent work on the relevance of gender relationships to such motivations is summarized. Four potentially significant social externalities associated with fertility behavior and use of the local natural resource base are identified. Three are shown to be pronatalist in their effects while the fourth is shown to be ambiguous in that it can be either pro or anti natalist. It is shown that one of the externalities may even provide an invidious link between fertility decisions and the use of the local natural resource base. The fourth type of externality is used to develop a theory of fertility transitions in the contemporary world. The theory views such transitions as disequilibrium phenomena.