Down to the river: marital movement and genetic structure on the Hispanic Portuguese border

Abstract

The aim of this study was to provide preliminary evidence on the impact of the River Minho on die genetic structure of the Hispanic-Portuguese populations that occupy its valley. The study was aimed to be descriptive rather than analytical, so ethnographic material was used as background information to predict the constraints imposed by the river's dual role as a political and geographic barrier. These constraints were then examined in an analysis of marital mobility and genetic structure in the valley in an investigation which involved two stages. Firstly, information derived from dispensations and isonymy was used to understand the degree of inbreeding of the populations and underlying genetic structure. Secondly, marital migration data was used to describe the admixture of the populations in terms of extent, direction and orientation of marital movement, to provide evidence on the barriers imposed by the River Minho. Ethnographic material was used in the interpretation of results. Results obtained point to patrilocal agricultural communities with high inbreeding, low admixture rates, high endogamy and local mate exchange where short-range movement predominates. These characteristics are present in both sides of the river, regardless of national affiliation or of the presence in the Portuguese area of a growing urban centre. Preliminary findings suggest that the River Minho may well be acting as a geographic rather than a political boundary to gene flow and genetic differentiation.