This article identifies four types of social externalities associated with
fertility behavior. Three are shown to be pronatalist in their effects. The
se three are exemplified by the way theories of economic growth treat ferti
lity and natural resources, the way population growth and economic stress i
n poor countries are seen by environmental and resource economists, and the
way development economists accommodate environmental stress in their analy
sis of poverty. It is shown that the fourth type of externality, in which c
hildren are regarded as an end in themselves, can even provide an invidious
link between fertility decisions and the use of the local natural-resource
base among poor rural households in poor countries. The fourth type is use
d to develop a theory of fertility transitions in the contemporary world; t
he theory views such transitions as disequilibrium phenomena.