The genetic structure and its recent evolution in a small isolated village in the French Pyrenees, Arthez-d'Asson, have been characterized by calculating the probabilities of origin of genes and inbreeding values at every generation since the 17th century.
Arthez-d'Asson appears to be one of the most inbred populations in France, with an inbreeding coefficient of approximately 0·5%. This is due first to genetical and cultural isolation, and secondly to migration out of the village towards towns at the turn of the century. The valley of Ouzom, in which Arthez-d'Asson lies, constitutes a hierarchical population and some cultural and genetical turnover is drawing back to the valley genes which have been absent for some generations.