Towards a New Horizon in Demographic Trends: The Combined Effects of 150 Years Life Expectancy and New Fertility Models

The hypothesis of a widespread and conclusive stabilization of the world’s population, the focus of recent United Nations’ forecasts, is obviously merely a reference model – the demographic transition. It is fairly plausible that initially populations will tend to follow this model. However, on the one hand, this is by no means certain and, on the other hand, it is unlikely that after this “transition” things will continue as before. Regarding the first point, the United Nations’ forecasts comprise, on both sides of the average hypothesis, “low” and “high” hypotheses whose difference with the former lies in the level to which fertility would tend, with mortality remaining unchanged (United Nations 1995). Among others, the United Nations is studying the consequences of a convergence of fertility levels towards 1.7 children per woman, on the one hand, and towards 2.5 on the other hand, as an alternative to the 2.1 that assures strict generation replacement. In both cases, the assumption that the world population’s size will stabilize is no longer valid. A level of 2.5 children per woman corresponds to an infinite growth, whereas with 1.7 children, growth would soon give place to diminution and the population would tend to become extinct.