Human Biology Open Access Pre-Prints

Document Type

Open Access Preprint

Anticipated Volume


Anticipated Issue



In the twentieth century Spain maintained some of the highest rates of consanguineous marriage in Europe. In many regions these rates were still high in the 1950s and 1960s, but then decreased rapidly, and by the 1970s a generalized transformation in mating patterns was underway. In the following decades the marriage of persons closely related by birth became rare. Consanguinity and inbreeding have been much studied in Spain, but almost exclusively in the central and northern regions of the country. This is the first study of a whole large diocese in the southern region of Andalusia. This paper is based on the analysis of 15,440 records of consanguineous unions registered between 1900 and 1979 in the Archbishopric of Granada in Andalusia. In this period, the rate of consanguinity up to second cousins was 5.51%, and the mean coefficient of inbreeding, α, was 2.04 × 10−3. There is a high range of variability within the research area. Thus, the rate of consanguinity was more than three times higher in rural areas (6.74%; α = 2.44 × 10−3) than in the capital city (2.03%; α = 0.93 × 10−3). There was a high frequency of unions between first cousins and first cousins once removed. These amounted to 35.3% and 13% of all consanguineous marriages, respectively, and contributed to 70% of α values. Consanguinity here has been strongly related to local endogamy. Thus 76% of all consanguineous couples were born in the same locality, and 89% resided in the same locality at marriage. By the end of the 1960s premarital migration increased and local endogamy started to decrease. On the other hand, inbreeding is inversely related to spatial endogamy. The more inbred couples such as uncles-nieces (C12) or first cousins (C22) show significantly higher exogamy rates and than second cousins (C33) and third cousins (C44), and higher rates of premarital migration. Neither males nor females in intra-family unions seem to be significantly younger than those in non-consanguineous unions. Considering their temporal evolution, consanguinity rates increased in the first third of the century, reaching a maximum in the late 1920s, when over 7.4% of all marriages were consanguineous (8.3% for the rural areas), and the resulting α value was the highest of the century (α = 2.71 × 10−3 for the whole diocese; α = 3.00 × 10−3 for the rural areas). Rates of inbreeding remained high until the 1950s and decreased thereafter in a period of accelerated emigration to cities, urbanization, industrialization and social modernization. Overall, levels of inbreeding are similar and sometimes larger than those found in dioceses in the Northwest of Spain, although marriages between uncle and niece were less common. Some of the counties in the diocese had very high consanguinity levels, not only the isolated area of La Alpujarra, previously studied, but also other ecological and historical micro-regions (comarcas). These results indicate that the widely accepted North-South divisions of the Iberian Peninsula in terms of consanguinity and inbreeding patterns require considerable re- evaluation.