The proposal seeks funds to complete the analysis of fertility change on the American frontier using a body of individual level data derived from a set of genealogies selected from the reposi- tories of the Utah Genealogical Society. This computerized file of approximately 170,000 family group sheets has been linked to the 1880 manuscript census providing the opportunity to evaluate the strengths and limitations of genealogical files Which constitute the core of the database of RGE (Resource for Genetic Epidemiology) of The University of Utah. Funding has previously supported database development and enhancements. Research to date has confirmed the limitations of the concept of natural fertility and a range of methodological and conceptual formulations arising from European studies of the fertility transition, based upon either aggregate data or more limited microlevel data sets. Funds are requested here to complete a series of studies which elaborate a sequence of analyses designed to test the general thesis that the Utah historical fertility transition (a) is marked by changes in birth spacing as well as truncation of childbearing, and (b) represents a form of adaptation to changing ecological and economic conditions. Two related sets of operational hypotheses are specified. A sequence of studies extend the research at the individual, family and community level. We explore, for example, at the individual level a series of sequential decision making models. Specific analytical models will vary somewhat, dependent upon initial investigations, but will generally conform to straightforward parity specific hazards models.