By the end of the 20th century most industrialized nations had undergone the so-called fertility transition, characterized by a reduction in fertility to below replacement level and a delay in age at initiation of child-bearing. An emerging concern is the severe economic and social consequences of this demographic decline. We present an overview of fertility changes in Italy in the second half of the 20th century and a mathematical model that may provide projections for the future of the demographic situation. Starting in 1950 the increment of the number of children born in Italy is initially positive; however, beginning in 1965 the trend suddenly becomes negative, and this negative trend further increased in 1975. A slight improvement is observed in 1980, followed by a stable situation beginning in 1987. Relevant socioeconomic and cultural events in Italy coincide with these variations in the fertility trend. Malnutrition, which had been endemic for centuries in some areas of central and southern Italy, disappeared rather abruptly in early 1960. The improvement in the economic situation was also associated with a decrease in illiteracy and with many sociocultural changes, with the emergence of new demands that decreased propensity for childbearing. The additional deceleration observed in 1975 corresponds to the diffusion of contraceptive procedures. The progression of sociocultural changes has led to a progressive liberation of women from the biological burden of childbearing. Two phenomena seem relevant in this context: women's emerging interest in entering the workforce and the possibility to disconnect sex from childbearing. The social function of feminism has overwhelmed the primary function of survival and diffusion of the species, giving rise to relevant and worrying demographic effects. However, the modern woman has an unconscious memory of her primary biological role, depending on both her genetic structure and cultural heritage, that should bring about a change in the present strong tendency to demographic decline. The basic notion of memory functions is widely recognized in sciences, for example, in the evolutionary theory of Darwin. Here, we introduce into the equations governing population growth a memory mechanism and a perturbation, and we estimate the reactions of the system to perturbations caused by environmental changes and subsequent delayed effects, such as those that appear in the birth rate beginning in 1965 and 1975. The mathematical modeling of the effects of perturbations of the fertility rate in the Italian population, with the introduction of a mathematical memory formalism, suggests that the effect is strongly reduced, with a relaxation time of about 10 years when the fertility rate approaches a stable value.
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Vol. 80 • No. 4