Writing the prologue to a volume on demography, on population evolution in Catalonia, Spain and the world, which analyses the main demographic phenomena that explain this evolution (fertility, mortality and migration) from different angles, is necessarily an exercise in meta-demography. It is a reflection on demography in three aspects: first, as a system for the reproduction of populations, major life events and the decisions surrounding them, which give rise to demographic behaviours alongside structural transformations; second, as a scientific discipline, given its role and the paradigm shift brought about by the information revolution and, therefore, by statistical data (so-called big data) and its processing; and thirdly, as a tool for political intervention, both in governing and managing population and in terms of knowledge about it, which has now become a battleground for democracy.

A risky and necessary exercise in these times of doom-laden readings. This is particularly so because, in the 21st century, most developed societies have moved towards complex systems of demographic reproduction, in which the migratory balance (immigration minus emigration) has become the determining factor in explaining population change, rather than natural growth (births minus deaths). All this comes in a context of very low fertility and lengthening life expectancy, leading to population structures in which the older population carries ever greater weight: what we term population ageing. If the birth of demography and its early momentum lay in the process we call demographic transition, the present day is marked by post-transitional societies, which, at different paces, are confronted with new challenges.

During the transition from a traditional regime, known in demographic terms as pre-transitional and marked by high fertility and high mortality (resulting in almost zero population growth), to a post-transitional regime (characterised by very low fertility and mortality, with equally low or negative growth), a remarkable biological energy saving is achieved. In between the two, rapid population growth, resulting from an early decline in mortality followed by a decline in fertility, was accompanied by its own spectres: such as the demographic explosion now replaced by fears of both population implosion and replacement at state and national level and fears regarding sustainability, in terms of the environment, on a planetary scale.

The interest and fascination that demography arouses is born, first of all, out of its connection to our own biological and social reality, both as individuals and the society in which we live. The phenomena under study are those that will mark our lives from the beginning (birth) to the end (death), taking in rites of passage, events which are generally marked by irreversibility. Thus, demography studies the formation and dissolution of unions and families, but also the milestones of our education, our entry into and exit from the labour market, our use of time, our health and illness, how we settle in the territory, and migrations, which are easy to see as reflections of our own life trajectories. It does so by taking into account sex and associated gender roles, ages and the social construction of chronology, which is also altered by demographic change, adding years to life. It does so by framing us within our generational group of contemporaries, with whom we share our year of birth and the experiences and memories of our common historical moment. This interest, as mentioned above, is also caused by aggregation, because demography studies the characteristics, evolution and development of the populations and sub-populations that make up the societies in which we live. It refers to “demographic metabolism” as the impact that the succession of generations will have on social change and on the territory. In short, it invites us to examine the relationship between demographic and social reproduction, with a predictive intention, which partly explains its central role in the political debate.

In these times of dizzying change, the discipline has witnessed a paradigm shift that favours observation from a micro perspective over the traditional macro approach in classical demographic analysis. This has come about due to the information revolution and the production and processing of big data. This not only clarifies individuals’ decision-making on demographic issues, but should also help reduce uncertainty. In the case of Spain in particular, this change in the statistical field has resulted in the old census being replaced by a new one, which is linked to government registers. This statistical revolution promises us more frequent statistical data on population and greater depth in the information provided. It has led to the adoption of interdisciplinary perspectives previously found only on the periphery of formal demography. It is a methodological quantum leap. The media presence of the discipline has also grown, compared to the marginal presence of demography in academia (as it is not considered an area of knowledge) and the limited presence of professionals in the public debate.

Finally, demography is at the heart of governance in relation to the birth of capitalism and political liberalism, in what the philosopher Michel Foucault termed biopolitics: the desire to promote life and the intangible aspect represented by the power of life, starting with the labour force. It is not surprising, then, that demography – demographic behaviours, structural changes, but above all future projections – occupies a central place in the Zeitgeist, steeped in the Gramscian anguish of still bearing witness to the birth of a new world whose outline we cannot yet discern.

The erosion of the foundations of democracy has been accompanied by what I term the practice of “recreational demography”, mostly by people with absolutely no relation to the discipline: the call for “demographic common sense”, anchored in wholly outdated paradigms, such as a particular reading of Malthusianism, which takes equilibrium as an axiom, by which to organise knowledge on populations. In this way, one can fall back on what are seemingly self-evident truths, drawing on both empiricism and the prestige of the quantitative approach in the objectivist tradition, while reducing the complexity of the demographic system to a mere set of communicating vessels, an approach that eventually promotes moral fables, conspiracy theories or self-fulfilling prophecies.

It is for these reasons that we welcome the proposal that the Centre for Contemporary Studies made to us at the Centre for Demographic Studies (CED) of the Universitat Autònoma de Barcelona to commission a special issue of the journal IDEES in which to present our own perspective. This invitation arises, we believe, from having crossed the threshold of eight million inhabitants in Catalonia at the end of 2023, and from the public celebration of the 40th anniversary of the CED in February 2024. But it is also justified by the changes that seem to be occurring in the ebb and flow of globalisation, inviting us to situate demography as a key element in the mutating geopolitical landscape, as Professor Massimo Livi-Bacci warns us in the introductory article, addressing the open future of the world’s population. As mentioned in the first paragraph of this foreword, we have divided the volume into three sections, based on geographical scale: the first section is on Catalonia; the second, on Spain, and the third, the world, offering a more clearly prospective aspect than the first two. The intention is not to provide thorough coverage of the demographic evolution of the three areas, but rather to use the difference in scales as complementary prisms.

The first section, written by Julián López Colás and Albert Esteve, director of the Centre for Demographic Studies, begins with a presentation of the demographic challenges facing the Catalonia of eight million inhabitants in three defining elements: its volume; its structure by sex and age; and its changing origins due to international immigration. The second article in this section, written by Pau Miret, tackles one of the classic issues of public debate: the impact of population trends on the pension system – on affiliations, benefits and pensions – and the dependency ratio. In the third article, I, Andreu Domingo, highlight the role of migration in demographic and social reproduction, showing how Catalonia has anticipated with much greater intensity what is happening in most developed countries. To close this first section, the fourth contribution, by Jordi Bayona, is closely linked to the previous one: it analyses school results by the origin of pupils, as an indicator of the integration of the immigrant population and their descendants.

The section on Spain as a whole begins with a reflection on the implications of the process of population ageing by Dolores Puga, who contrasts the alarmist discourse on this demographic change with reality. In the second article, Roberta Rutigliano examines the relationship between the decline in fertility – which, in both the Spanish and Catalan cases, has been among the very highest – and the socioeconomic factors that help to explain its trends. To close the section on Spain, Diederick Boertien uses the data from the 2021 census to consider the impact of fertility on family transformations.

In the last section, covering the world as a whole, we return to the three essential phenomena of which demography consists. The first article provides a reflection on migration by Leo van Wissen, based on demographic and economic disparities in the world’s major regions, as well as recent changes in migration policy. Iñaki Permanyer then reflects on worldwide trends since the 1970s, in which increasing longevity is a key factor. Finally, Alícia Adserà presents an assessment of fertility decline on a global scale and analyses possible policies to address the phenomenon.

Due to limitations on space, we realise we have sacrificed the presentation of crucial issues: from the long-term view of historical demography to projections of future population growth and rural depopulation. Nor have we provided in-depth analysis of rather complex issues. But we hope we have compensated for these shortcomings by making every effort to use both comprehensible language and a rigorous, innovative approach to the challenges posed by population changes. In addition to providing a varied overview of changes in the main demographic phenomena at three different scales, the main purpose of this issue that each brushstroke in this volume contributes constructively to the public debate on the implications of demographic developments from a professional perspective.