The genetic and demographic impact of in-migrants in a largely endogamous community

Abstract

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.

An abnormal concentration of cases of Rendu-Osler disease in the Valserine valley of the French Jura: a genealogical and demographic study

“…Most of the isolates in Western European mountain populations have tended to disappear during the present century. A study of the village of Toerbel in the Swiss Alps has shown that, in spite of a high rate of endogamy, a small number of immigrants has resulted in a non-negligible modification of the local gene pool; 38% of the genes present in 1978 were contributed by the immigrants (Hagaman, Ellis and Netting 1978). In France, genetic isolation has been found to have been most pronounced in the village of Ouzom in the Pyrenees.…”

PROFESSIONS, GENERATIONS AND REPRODUCTIVE DYNAMICS OF A FRENCH ALPINE POPULATION (16th–20th CENTURIES)

“…The demographic data collected over several generations suggest that the Vallouise community was not a sociologically homogeneous entity. A divided society was observed during the nearly four centuries examined, despite a relatively high mean endogamy and consanguinity (Hagaman et al, 1978;Serre et al, 1985;Viazzo, 1989). The social strata resulting from the matrimonial choices and the professions of the heads of families were quite marked.…”

“…Here again, too many children would have led to impoverishment through partition. Outside the French context, several surveys have partially tackled these problems and in each case social groups practised different behaviours regarding their descent (Wrigley, 1966;Abelson, 1978b;Hagaman et al, 1978). In other instances, socio-professional homogamy was practised but this mainly concerned the strategy of alliance (Darrow, 1985).…”

Biologie et histoire de la population

“…Dans les zones rurales, il est également possible d'intégrer une variable sociale à ces patronymes et à leur dynamique géographique, par exemple en distinguant les patronymes portés par 11 des lignées de propriétaires fonciers ou ceux portés par des non-propriétaires. Des observations de cet ordre se retrouvent, par exemple, dans les Pyrénées, (Abelson, 1978), dans les Alpes suisses (Hagaman et al, 1978) et dans le Limousin (Crognier et al, 1984).…”