EARLY SELECTION AND SEX COMPOSITION IN ITALY - A STUDY AT THE REGIONAL LEVEL

We have chosen four Italian regions with different degrees of industri alization and socioeconomic levels to study environmental differences in the sex ratio. The improvement in living and sanitary conditions du ring the last century has led to a progressive reduction in early male extramortality, and the sex ratio at birth has been almost unchanged at least to the first year of life and probably up to reproductive age . To investigate whether socioeconomic, cultural, or biological factor s still influence the sex ratio at birth, we studied the stillbirth ra te and the relations between newborn viability and sex composition as a function of maternal age and educational level. Our results suggest that in less favorable environments early selection against male newbo rns is almost twice that against female newborns when the mothers are the least favored for socioeconomic status, cultural level, and biolog ical conditions (older than 39 years).