This article examines the descendants of four cohorts of couples formed in the seventeenth and eighteenth centuries (two cohorts in two French mountain valleys and one on the Ile-d'Orléans in Quebec). The children are separated into four categories according to their fate (deceased while still unmarried, unknown fate, married but childless, "useful children"). "Useful children", a concept used in population genetics, are those who in turn bear children. In all three places, the useful children represent only from 26 to 31% of births. The study goes on to measure the contributions made by these couples to the next generation. In the mean, each couple gave birth to little over one useful child. But the contributions of couples turns out to be very unequal. Depending on the place, from 36 to 53% of couples left no useful children behind them, while a small minority of couples made an ample contribution to the next generation. The same measure is reproduced in the constitution of the next generation, thereby showing that inequality of couples in terms of reproduction is perpetuated.