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Demography

The statistical study of human populations (structure and change), the factors behind their dynamics and the consequences of population change.

 

The word démographie was first used in its current sense by Achille Guillard in 1855 but this marks the belated baptism rather than the birth of the discipline. The first stones were laid in the 17th and 18th centuries by the “political arithmetic” of John Graunt, Edmond Halley, Johann Peter Süssmilch, Willem Kersseboom, Antoine Deparcieux, Pehr Wargentin and others, with the common aim of applying the sciences of numbers (mathematics, statistics, probabilities) to a political purpose (human government). Indeed, the demographer must begin by reducing reality to measurable, computable data in order to describe, analyse and understand the mechanisms underlying population composition and change. The understanding of population dynamics lies at the heart of the discipline, and demography only really came of age with the qualitative and quantitative study of the causes and consequences of population change for individuals and societies.

Although demographic methods can be applied to any group that is subject to change (whether living or inanimate), demography in the strict sense deals solely with human populations, excluding animals from its usual objects of study. The simplest human group to define is obviously the entire set of human beings living on Earth, but demography can just as well apply to any fraction of that set, identified by one or more criteria: territory, religion, language, school attendance, economic activity, disease, gender, blood group, etc. Among these criteria there is a natural focus upon residence in a socially significant territory: a country, a region, a city, etc.

 

Understanding population dynamics


At any given time, a population is characterized by its size (number of individuals) and composition (frequency of the recorded values for the characteristics under study). But far from being fixed, this population varies constantly as people arrive (births, immigration) and depart (deaths, emigration). The propensity to reproduce, migrate or die is closely dependent on age and sex, so the first task is to calculate fertility, mortality and migration rates by sex and age in order to identify the functions (in the mathematical sense) of fertility, mortality and migration that determine change in a population and, in turn, its age-sex composition. It is by combining these various functions in population models that the permanent interaction between demographic structure and change becomes clear. While a single combination of mortality, fertility and migration functions may give rise to different population growth rates for populations with different age-sex structures, conversely, a population’s structure is wholly defined by the past history of its variation. Two populations, whatever their initial structure, exposed over the long term to the same combination of fertility, mortality and migration, will ultimately achieve the same structure: this is Lotka’s equation (1934, 1939).

 

Finding the determinants of the forces for change


Clearly, then, a major part of demographers’ work involves attempting to explain what lies behind changes in demographic behaviour. Basically, fertility, mortality and migration depend on similar processes: starting from biological preconditions inherent to the human species, the propensities to reproduce, migrate and die are strongly influenced by a highly complex set of determinants, both direct and indirect. These may be ecological, geographical, economic, sociological, political, cultural, philosophical, metaphysical, etc., and they vary over time and between societies. As a result of these determinants, each population, at every point in its history, acquires predispositions and adopts individual and collective behaviours that determine its dynamics. Each of the three major forces of demographic change, however, responds to these influences in a highly specific way. Each is a focus for specialization among demographers, so that fertility, mortality and migration have become virtually autonomous research fields with their own specific topics and methods, some of which stray far from the central question of population dynamics.

 

Retracing history in order to predict the future


As a human science, demography cannot be based on experiment. Its only possible source of evidence is the history and diversity of observable situations. Hence the importance of historical demography and comparative studies. History looms large in demographers’ thinking because humanity has undergone a major demographic revolution in the 250 years since the mid-18th century. In the latter half of the 20th century, it was even claimed that the theory of demographic transition devised to account for this upheaval (Landry, 1934; Davis, 1945; Notestein, 1945) was the major key not only for understanding past and current changes but also for speculating about future developments. Indeed, if the UN’s experts in the late 1950s were able to predict that the Earth would have a population of 6 billion by 2000, it was because the theory of demographic transition gave them, at that time, a particularly accurate set of hypotheses for the changing population dynamics of developing countries, seen as the main drivers of future global population trends. Since then it has become clear that the complexity of the phenomena involved, particularly in Europe but also already in many developing countries, cannot be reduced to this single paradigm. Demographers are now struggling to find a theory to predict future population trends by the end, or even the middle, of the present century.

 

Assessing consequences and evaluating policies


Finally, should we and can we attempt to influence population dynamics? Views on this issue have varied over time and demographers have obviously played a major part in the debate. In practice, demographic behaviour is so intimately connected with social life that any policy, consciously or unconsciously, has demographic consequences, and any demographic change affects the development of the society as well as the policies. Demographers therefore, must also reflect on these aspects. Not that they are best placed to judge the validity of policies but rather that their research must help to clearly identify the consequences of demographic change in all areas of economic, social, cultural and political life, and at all levels (individual, family, nation, world). Research must also examine the efficacy of population policies that explicitly aim to influence fertility, health or migration, and policies that seek to prepare society for the observed or predictable consequences of demographic change.


As an arithmetic of life and death, demography is, therefore, anything but a dry computation of individuals dehumanized in statistical tables. Rather, in its purpose and approach, it is a truly human science. Not only does it study the most intimate and crucial events for each human being, namely birth, parenthood, and death, but it also draws upon the history of peoples to retrace that of humanity as a whole.

 

Jacques Vallin 2014 

 

References

Davis, Kingsley (ed.), 1945. – “The world demographic transition”, Annals of the American Academy of Political and Social Science, n° 273, p. 1-11.

Guillard, Achille, 1855. – Éléments de statistique humaine, ou démographie comparée. – Paris, Guillaumin & Cie Libraire, 376 p.

Landry, Adolphe, 1934. – La révolution démographique. Étude et essai sur les problèmes de la population. – Paris, Librairie du recueil Sirey, 231 p. (republished 1982, Paris, Institut national d’études démographiques, 231 p.).

Lotka, Alfred J., 1934. – Théorie analytique des associations biologiques. Première partie: principes. – Paris, Herman & Cie, 150 p. (Actualités scientifiques et industrielles, n° 187).

Lotka, Alfred J., 1939. – Théorie analytique des associations biologiques. Deuxième partie: analyse démographique avec application particulière à l’espèce humaine. – Paris, Herman & Cie, 139 p. (Actualités scientifiques et industrielles, n° 780); translated in 1998 as Analytical Theory of Biological Populations. New York: Plenum Press.

Notestein, Frank W., 1945. – “Population, the long view”, Theodore W. Schultz (ed.), Food for the World, p. 36-57. – Chicago, University of Chicago Press, 367 p.

 

Note : This article is an English translation of the article Jacques Vallin wrote in French for the Dictionnaire de démographie et des sciences de la population, edited by France Meslé, Laurent Toulemon and Jacques Véron, published in 2011 by Armand Colin. 

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