 If people have economic and social opportunities that make it advantageous to limit fertility they will be more willing to limit it.There must be economic and psychosocial costs involved such as the cost of birth control or abortions.It is hypothesized that the observed trend in many countries of having fewer children has come about as a response to increased life expectancy, reduced childhood mortality, improved female literacy and independence, and urbanization that all result from increased GDP per capita, consistent with the demographic transition model.