Sex Ratio and Individual Variability Analysis within mountain Communities of the Western Alps

Average values worldwide show a birth ratio of 105-106 males each 100 females, nevertheless the sex ratio changes from populations to populations and also in time. The cause of these variations are not well known, although is known a certain genetic influence in particular from the father. Among the factors which have a role on the sex ratio: the age of the parents, the birth order, the social economical status, nutritional state of the mother, the environmental ors such as the season. In the present work is assessed the sex ratio in relation with the season of the births (and related conception) in two western mountain villages Chiomonte (high Susa Valley) and Argentière la Bessée (Hautes Alpes). The sex ratio observed from the end of the XVII century to the beginning of the XX century are part of the range of variability for the two villages although there are some periods in which the sex ratio go off the average values observed. A bayesan hierarchic model has been tested on Chiomonte families based on individual variability of the sex ratio. The model deals with the fact that each couple getting married lead to the creation of children mainly of a sex or of the other and that this represents the same family lines of the respective parents.