A considerable number of studies on historical and some third world populations have reached a magnificent consensus that both mortality and fertility do respond to economic changes in a surprisingly shared pattern. Such response, however, remains a great deal of controversy, obscure and inconsistency in the secular industrialized countries. As a result, a great variety of alternative hypotheses have been developed to account for the secular decline in mortality and fertility. While there is widespread interest in this subject with particular focus on short-term fluctuations, I further study the impact of severe economic crises on these demographic variables.