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.
PIP: Researchers used 1961 census data from Italy to study fertility in Sardinia when malaria was endemic. Results show differential fertility between women living in 335 towns and villages with varying degrees of malaria. The mean number of children/woman rose significantly from areas of low to medium to high incidence of malaria (p .001). Further, a 1984 survey on the association between fertility and diseases showed that in areas of intense transmission of malaria, infant mortality was high, but surviving adults were greatly immunized and pregnant women were protected to some degree from the risks of placental parasitization and consequent fetal loss or stillbirths. On the other hand, in areas of medium or low malarial endemicity, infant mortality was low and surviving adults were not immunized enough to protect them from malaria. Further, pregnant women whose immune systems are naturally suppressed often developed fever, anemia, and placenta parasitization. In the 1960s, a researcher analyzed 52 Sardinian villages for thalassemia and G-6-PD deficiency. The results showed that for both genes, the overall frequencies of heterozygotes were significantly higher in the areas of high malarial endemicity (p.001). When the researcher compared the variation between villages, however, the difference was not significant, especially for G-6-PD deficiency. Therefore, the increased fertility in high endemic areas may be due to the greater acquired immunity and a higher frequency of heterozygotes for malarial genes, such as thalassemia and G-6-PD deficiency. In addition, as the level of education increased the fertility rate decreased. Fertility was lower in urban areas (20,000 inhabitants) than in rural areas.