Document Type



This study examines the demographic structure and the changing opportunity for selection in a small, agricultural community in Central Pennsylvania. Fertility is examined for the years 1850, 1860, 1870, 1880, and 1900, utilizing the child-woman ratio and age-specific birth rates. Mortality is examined for two periods in which accurate records exist, 1845 to 1854 and 1895 to 1904. Life-tables were constructed using age-specific death rates, and bounds of standard error were calculated for each time period. Crow’s index of selection was calculated for 1850 and 1900.The study population had moderate levels of fertility and mortality in 1850. These levels had decreased by 1900. Crow’s index reflects these decreases, as the fertility component was 0.324 in 1850 and 0.308 in 1900. The mortality component was 0.318 in 1850 and 0.225 in 1900. Trends reported in other studies of opportunity for selection show similar tendencies. Migration was important, for there was a 70% turnover of the population every ten years. Drift and inbreeding affected the population very little, as the mean index of isolation was high, 134.5, and there were no consanguineous matings whose offspring remained in the Township after 1850.