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As part of an interdisciplinary research program on Alpine populations, we studied the biodemographic evolution of two populations of the Dauphiné in the period 1690-1799. We analyzed several indexes derived from surname analysis to infer the genetic structure of the populations. Although situated in the same area of the Dauphiné, the two communities of Vallouise and Chiomonte had different biodemographic characteristics. Vallouise was heavily populated but genetically homogeneous, whereas Chiomonte was less populated but more heterogeneous. The two districts also differed in geographic position: Vallouise was a glacier-enclosed valley that did not attract new inhabitants; Chiomonte was situated in an open valley served by important roads and thuswas able to attract many newinhabitants. The demographic differences between the two populations explain the differences in genetic structure. The index of isonymous relationship (RI) being different from 0 is due to the rare marriages between members of the two populations. Because RI is based on surnames, which are mostly polyphyletic, it can overestimate the genetic relationships between the populations, as in the case of consanguinity assessed by matrimonial isonymy. [ABSTRACT FROM AUTHOR]

As part of a survey of the biological history of Alpine populations, the lineages of all the families of the Vallouise valley (a French 'department' of the Hautes Alpes) have been reconstructed over several centuries. The genealogies have been included in a computerized population record, known as 'Vallouise in the Briançon area (14th-20th centuries)', using the French-Canadian programme Analypop. Most of the professions of the family heads were included in the files. In this study, various profession groups were identified and their descents determined over successive generations. In this mountain area, where over 92% of marriages took place among relatives during the 19th century, the profession groups modulated their descents according to chosen strategies, sometimes with considerable differences among groups but with a remarkable consistency of behaviour. Moreover, there was weak interpenetration in the descents of each profession at both the 2nd and 3rd generations.

Sociocultural factors play a crucial role in the variation of consanguinity in a population. The choice of specific matrimonial strategies can favor the closure or opening of the group to the outside, whereas differential fertility affects the gene flow from one generation to another. In the present study we analyzed the role of socioprofessional groups in the maintenance of endogamy and consanguinity in a French Alpine valley: Vallouise in the Briançon area. In mountain environments, where the reproductive space is limited and quickly saturated, the autochthonous families adopt diversified matrimonial strategies. These marriage practices tend to prevent fragmentation of agricultural property. We analyzed the matrimonial behavior in the two main social groups of this population (décideurs and farmers) from 1550 to 1849. To better understand the behavior of the two social groups, we considered the two components of consanguinity, close and distant. Our study showed that the two groups had similar behavior regarding consanguinity. The way to prevent fragmentation of the patrimony was to choose a consanguineous spouse. This type of strategy inevitably leads to a high percentage of endogamy, which in this region of the Alps exceeded 90% through many centuries.

The present study considers the evolution of consanguinity in the Vallouise, a high glacial valley in the French Alps. The genealogical method was used to estimate consanguinity in this Alpine population from the 17th to the 19th centuries. This method was then compared with three other methods used to measure consanguinity. The results indicate that while consanguinity increased through time (marriage dispensations and genealogies), the structural consanguinity (isonymy) was very stable throughout the entire period.