During the 1930s in the Venezuelan village of San Carlos de Río Negro, the Baré practiced cross-cousin marriage. However, by the 1980s they married hypergamously among the Curripaco, Geral, and Criollos, all of whom had recently migrated to the village. There is considerable historical material on San Carlos, which when coupled with fieldwork, facilitate the formulation of a number of hypotheses to test what best accounts for this transformation of marital rules. Lévi-Strauss predicted the causes of the breakdown of elementary kinship structures and the creation of complex ones; this chapter suggests an alternative scenario. In a parallel case, Curripaco women migrated to San Carlos in the 1970s and 1980s, could marry someone employed directly or indirectly in the government project, Codesur (Comisión para el Desarrollo del Sur), and became incorporated into the complex kinship structure of this ex–rubber boom village. This chapter suggests their social transformation sheds light on the Baré transformation of some forty years earlier.