POPULATION. - The totality of all inhabitants of a country, a region, a city, etc. Its size and composition vary continuously due to births and deaths (natural movement), and, within a given area, also due to migrations (social movement). Therefore, it is quantitatively and qualitatively determinable if circumscribed in space, time, and under normal conditions. It can be considered from various perspectives, first and foremost in terms of its absolute size or mass, its relative size or density, and its growth.
I. THE ABSOLUTE SIZE OF THE POPULATION
The absolute size of the population is determined through the complex of operations known as a *census*: at a specific moment on a given day, the state organ expressly entrusted by law with this task proceeds to enumerate all persons found within the entire territory of the state by means of special forms, called household sheets (for family units) and conviviality sheets (for non-family units, such as hotels, barracks, convents, colleges, etc.). The totality of persons present in the state’s territory at the time of the census constitutes the so-called present or de facto population. In Italy, as of 4 November 1951 (the most recent general census), the present or de facto population was 46,737,704 persons. This, however, differs from the resident population, which consists of all persons whose domicile is in a given administrative district (municipality), some of whom may be temporarily absent at the time of the census because they are in another municipality or even outside the state’s territory. The size of the resident population is therefore obtained by adding to the total number of present persons the number of temporarily absent persons and subtracting the number of temporarily present persons who do not have their domicile in the municipality. According to current provisions in Italy, the resident population is taken as the legal population until another census is conducted. In Italy, as of 4 November 1951, according to the initial results of the latest census, the resident population was 47,138,235, of which 23,085,776 were male and 24,052,459 were female.Knowledge of the number of inhabitants is of great importance not only scientifically, as it constitutes the standard reference point in the study of social phenomena, but also practically, since it forms the basis of the political and administrative organization of the state, for whose purposes the resident population is taken as the legal population. In Italy, for example, the number of municipal councillors and assessors, the rates for certain local taxes (family tax, rental value), the number of notaries, and the number of state schools are all determined based on the number of inhabitants in municipalities and provinces. Even in international relations, knowledge of the population size of various countries is often an indispensable requirement. However, not all countries possess reliable data on the absolute number of inhabitants; in many, censuses are not conducted, and the number of inhabitants is estimated based on statistical indicators. Demographers have indeed had to resort to such estimates to determine the world population and its major divisions. In 1935, it was estimated at around 2,076 million, of which 524 million in Europe, 261 in America, 10 in Oceania, 145 in Africa, and 1,136 in Asia.
But beyond the absolute size of the population, it is also important to know its *structure*, that is, its composition by sex, age, marital status, profession or occupational condition, etc. The sex composition is relatively constant over time and space, except in countries with significant sex-selective migration; generally, the number of females slightly exceeds that of males due to the higher mortality rate among the latter. This is the case, for example, in European countries. In America, Australia, and New Zealand, there is a slight male predominance, plausibly due to immigration. Variations, whether increases or decreases, which are largely attributable to migratory movements or other social phenomena, can also occur over time. Thus, in Italy, the 1881 census revealed a very slight male predominance (1,005 males per 1,000 females), whereas in 1936 the ratio was 943 males per 1,000 females.
Far more variable, however, both over time and across space, are other characteristics (age, marital status, profession or condition). The age distribution of the population varies greatly from country to country and, within the same country, from one period to another. It is estimated that in 1940, the population under 15 years of age was 29.6% in Italy, 23.7% in France, 21.6% in Germany, and 36.2% in the U.S.S.R. Considerable differences are also found with regard to marital status. The proportions of single, married, widowed, separated, and divorced persons vary significantly from country to country; where divorce is permitted, the proportion of divorced persons (even excluding those who have remarried) differs greatly depending on the ease with which the law allows for the dissolution of marriage. Even more profound are the differences from country to country with regard to profession or occupational condition, and within the same country, from one region to another. According to the results of one survey, in the provinces of Sicily, persons in non-occupational conditions constituted 67% of the total, while in the province of Milan, they constituted 52%. The same proportion of various professions is linked to the socio-economic conditions of the country and region: where agriculture predominates, agricultural professions predominate, and so on.
II. POPULATION DENSITY
In addition to absolute size, it is also important to know the relative size or density. This is obtained by dividing the absolute size by the surface area, and the quotient expresses the number of inhabitants per square kilometer. However, when making comparisons between states or even smaller administrative divisions, it must be taken into account that the habitable part of the territory, or ecumene, varies greatly. In Italy, the population density, which was 139.6 in 1936, rose to 153.4 according to the census of 4 November 1951. However, it varies greatly from region to region; it is higher in Campania (314), Liguria (282), Lombardy (263), Veneto (210), and Lazio (200); and lower in Sardinia (50), Basilicata (62), and Umbria (94). According to demographers’ estimates, the population density in the various continents around 1935 was as follows: Europe 45.9; America 6.4; Oceania 1.2; Africa 4.8; Asia 27.1. Within smaller administrative divisions, a distinction is made between concentrated population, i.e., that residing in urban centers, and dispersed population; between urban population, i.e., that residing in cities, and rural population.### III. GROWTH OF POPULATION
As noted at the outset, the size and composition of the population are in constant flux from one moment to the next, due to births and deaths (natural movement) and migrations (social movement). The study of these movements is therefore of particular importance, since it is their intensity and direction that determine variations in the composition and size of the population. Such movements are recorded, for births and deaths, in civil registries. The difference between the number of births and the number of deaths over a given period constitutes the natural increase for that period. To this must be added or subtracted the social increase or decrease, i.e., the difference between emigrants and immigrants. Population growth is determined over longer intervals through censuses. This growth can be measured both in absolute terms and in relative terms. A relative measure is provided by the average annual growth rate, which demographers liken to that of a sum invested at compound interest, where the population at the initial moment constitutes the principal and the population at the end of the period constitutes the final amount. It is evident that the growth of the population, both in absolute and relative terms, is influenced by the various factors mentioned above, in proportions that vary greatly from country to country and, within the same country, from one period to another. Such analysis is the particular domain of demography (v.).
### IV. THEORIES ON POPULATION
The study of the factors determining population growth has long fascinated demographers and sociologists. The founder of demography himself, J. Graunt, noted in 1662 a tendency toward population growth. Later, A. Petty (1682) addressed the subject directly and hypothesized that the population tends to double in about 200 years. Subsequently, the German Protestant pastor G. P. Süssmilch (1707–67), in his work *Die göttliche Ordnung in den Veränderungen des menschlichen Geschlechts* (1741), observed that population tends to multiply due to the excess of births over deaths and would double at regular intervals if the increase in inhabitants were accompanied by a proportional increase in the means of subsistence. The question was taken up again by G. Ortes (1773), who argued that population tends to multiply geometrically every 30 years, if not restrained by various economic and social factors. This brings us to 1798, MALTHUS, THOMAS ROBERT (v.), in his work *An Essay on the Principle of Population*, formulated the theory that would gain such resonance and to which he owes his fame. From Malthus’s theory there subsequently arose the so-called neo-Malthusian movement (v. NEO-MALTHUSIANESIMO).
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