1. Introduction

The more developed countries are experiencing an inexorable decline with respect to the population. Aging is reaching intolerable levels in the economy, both from the active (available workers) and the passive (e.g. health costs, pensions) point of view, redesigning a worrying scenario for the near future.

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On the other hand, fertility in many countries, and particularly in Italy, reaches such low levels that the prospects of a recovery, in terms of quantity, now seem impractical, unless of sociodemographic upheavals rather unlikely.

In this context, most likely, from the point of view of demographic and social, he is starting a new era in which the main actors on the global stage will certainly be different from those in the field today, with completely obscure scenarios and still in the making.

Surely, however, this situation has generated fears and concerns about the future of the population, especially for some signals that in the course of 2015 were recorded in Italy, such as the surge in mortality, especially with regard to older ages, where some observers have linked this phenomenon to a reduction in public spending in the health sector, a situation that would have penalized, certainly, the older age groups. On closer analysis, however, we realize that, precisely due to aging of the population of elderly, quotas have gradually increased, causing a swollen available to die, with the same probability of death.

We are at the dawn of a new world, and the population of the planet will be substantially transformed over the next 30–40 years, according to the latest update made by the World Bank (World Population Prospects: The 2015 Revision. New York: United Nations). The world population has reached 7 billion people in 2015 and will rise to 9 billion around 2050, an increase due mainly to developing countries.

But the most significant fact is that few countries will contribute to more than half the increase worldwide, especially this will be due to the contribution of India, Pakistan, Nigeria, Ethiopia, the United States, Congo, Tanzania, China, and Bangladesh.

The World Bank, which had already produced in the 1980s of the projections that had left the whole world into turmoil, when it predicted that the world population would reach 20 billion people already in 2020, has, as a precautionary measure, developed based on the assumption that projections fertility decline through woman from the current global level of 2.5 children to 2.1, from now until 2050. Population of the 49 least developed countries is growing still faster than the rest of the world, at a pace of 2–3% a year, as published by the Population Division.

While it is expected that the population of developing countries as a whole will increase from 6 billion today to 7.9 billion in 2050, the population of more developed regions will not change much, passing from 1.23 to 1.28 billion.

The latter would have had to decrease to 1.15 billion were it not for the projected net rate of migration from developing countries to developed countries, which provides for the annual shift of about 2–2.5 million people over the next 30–40 years.

Also, according to the projections of the World Bank, the scenario is even more disheartening for Europe, as a whole, in fact, to the middle of the twenty-first century the population of the old continent not even reach 8% of the world's population and, even more worrying, this will be characterized by a high seniority, against the rest of the world, however, will feature a very young population
