The relationship between inbreeding, migration and population density in Norway.

An investigation of the present levels of inbreeding and the proportion of non-migrants (residents in municipality of birth) in rural districts of Norway reveals a relationship between these two characteristics. There is a steady upward trend from 0.39% first- and second-cousin marriages in municipalities with less than 50% non-migrants to 4.3% such consanguineous matings in municipalities where 85% or more of the inhabitants are non-migrants. There is also a significant negative correlation (rs=-0.86, N=18) between inbreeding and population density per square km by county in Norway. In rural districts of Norway maximum inbreeding is observed in sparsley populated areas with maximum proportion of non-migrants, and the ratio of second- to first-cousin marriages ranges between 3.4 and 4.1. A similar high ratio (3.7) is also encountered in densely populated trading and industrial municipalities and in the smaller towns, whereas the semi-urban municipalities and the larger towns have the lowest inbreeding recorded and also a low ratio (1.9). The lowest proportion of non-migrants (39.3%) is recorded in the semi-urban municipalities.