On the basis of references to genealogy and blood, the author analyzes some evolutions in Basque nationalist ideologies. By re-establishing the importance of marriage, he studies the grogressive erosion of a sort of radical ius sanguinis considered to be the key to perpetuation of nation purity by the first nationalists. If genealogy expresses the Basque identity through references to autochtonous family names, the moment of formation of genealogies, the marriage, clearly remains potentially subversive. Racial nationalism progressively changes into a nationalism that puts more emphasis on topics such as territory, language and political will, as the Basque socio-genealogical fabric changes.