It must be pointed out here that this high rate of family-mortality bore no relation to the economic status of these lignages. Death strikes equally rich and poor, baron and squire, the eminent and the insignificant. Causes general to the times were at work: high mortality in spite of a high birth-rate; the hazards of war; those of political upheavals, with their train of attainders and confiscations - which, at least up to the fourteenth century, were less important in France than in England. Other causes are particular to such social groups as attain some sort of eminence. Thus, the necessity, in order to avoid splitting estates through partition between children, of sending younger sons into the Church, would sooner or later bring the line to an untimely end. [. . .]
New families were thus constantly replacing the dying ones. Some of the newcomers came from junior branches of the local nobility itself, who, through marriage with heiresses, replaced in their lordships the old lines now extinct.'9 Others belonged to the gentry of neighbouring provinces and settled in Forez in the same way.20 None of these was really bringing new blood into an otherwise dwindling social class. More important for our purpose are the new men, those who suddenly appeared as knights or squires with no known ancestry in the nobility and who, given the chance, founded new noble lignages. To know where they came from, we must work mostly by inference and generalise from a few well-documented cases. We can be sure, however, that these newcomers were not recruited from a well-defined social group, but came from widely different strata [. . .]
In a country and at a time when society was almost entirely rural, the largest group of new noblemen came, so it seems, from peasant- stock. In Forez, there was no sharp dividing line between peasants and poor squires, except their different birth. By the thirteenth century, serfdom was as unknown there as in Normandy; all peasants were freemen, even those who owed tallage and a few labour service restricted to one or two days a year.
[Edouard Perroy. Social Mobility among the French Noblesse in the Later Middle Ages]