Document Type



The structure of the different categories of multiple consanguineous marriages (MCMs) and their historical variation patterns are analyzed in the Spanish dioceses of Alava (Basque Country) and Sigiienza-Guadalajara (Castile). Consanguineous marriages, up to third cousins, were taken from ecclesiastical dispensations, and the periods studied were 1831-1980 for Alava and 1861-1980 for Sigiienza-Guadalajara. Significant differences exist in the MCM rates in the two Spanish areas. In this study a model is proposed to prove that in a general population there may be dependence between MCM rates for specific relationships and the frequencies of those types of relationships in the form of simple consanguineous marriages (SCMs). The effects of avoidance and preferentiality and of underreporting are discussed to explain the deviations between observed and expected consanguineous marriage frequencies. A limit to the weight of remote consanguinity on the population inbreeding coefficient F is determined. The relationship between Ft1Fs and ms values from our two Spanish populations are fitted to curvilinear regressions. FT is the total population inbreeding coefficient, Fs is the contribution to Fr from SCMs, and ms is the relative observed frequency of SCMs in the general population.