Excessive twinning in a rural American genealogy

A family record of 1693 descendants in rural Missouri exhibits a twinning rate of 2 X 2%. Weinberg's Differential Rule estimates the level of monozygosity in this twin sample at 61-83%, unlike previous results dominated by dizygosity . These historical data cannot directly support a genetic basis for monozygosity though. Clinical studies seem the best solution to the genetics of twinning.