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Taking account of the demographic and socioeconomic evolution of the population (Isle-aux-Coudres, Quebec), mother-daughter correlations and sister-sister correlations were computed on waiting times to first birth and first birth intervals. The results suggest that heritability of the correspond­ing fertility factors, namely fecundity and post-partum sterility, were higher than previously reported heritability values of fertility. Furthermore, the experimental design underlines the view' that migrant people might be genetically different from sedentary people as far as fecundity is concerned.