Fertility and malaria in Sardinia.

Using data from the 1961 Italian census, the study of fertility in Sardinia when malaria was endemic shows differential fertility between women living in areas with differing degrees of malaria. Cultural factors measured by women's level of education are negatively correlated with fertility, just as the 'urban' character of the area in which the women lived has a lowering effect on the fertility rate. The hypothesis of differential mortality according to social class, affecting lower-class women and in particular the more prolific among them, seems to be supported by data analysed through time. The subdivision of Sardinian towns and villages into those with a 'low' and a 'high' malaria rate was made on the basis of the classification given by Fermi in a period corresponding to the overall period of fertility of the women considered. Hypotheses about a greater acquired immunity and a higher frequency of heterozygotes for malarial genes, like thalassaemia and G-6-PD deficiency, in the area where malaria was more intense, are proposed to explain the higher fitness of women living in this area. The comparison between frequencies of heterozygotes for thalassaemia and G-6-PD deficiency, obtained by Siniscalco et al. for Sardinian villages in the two different malaria-infested areas, shows a significant difference when the areas are examined as a whole, but a great variability (principally for G-6-PD deficiency) between villages. Changes in ecological factors could have modified the geographical distribution of malaria today, compared with the distribution that may have determined the frequencies of heterozygotes many years ago.