The genetic and demographic impact of immigrants in a largely endogamous community

Historical demographic data extending back approximately 300 years were analysed to determine the demographic and genetic impact of in-migrants to an endogamous Swiss Alpine village. In-migrants were involved in only 14% of the marriages recorded in the village. In addition, only slightly more than 50% of the in-migrants were represented in the 1970 gene pool of the village. However, in-migrants accounted for nearly 38% of this gene pool. This seemingly anomalous situation can be explained by the fact that while the fertility of in-migrants and the marriage rate among their children are reduced (accounting for the near 50% "drop-our rate" of in-migrants from the gene pool), the fertility of the children of in-migrants and the marriage rate among the grandchildren of in-migrants are increased relative to village natives (accounting for the high proportion of genes in the gene pool ultimately attributable to in-migrants). Our results clearly demonstrate that although this community forms an endogamous population, it is definitely not a genetic isolate. Other investigators are cautioned against automatic invocation of the simplifying (and, thus, extremely tempting) assumption that endogamy is equivalent to genetic isolation.