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The expression "population theory" (cf. 101-1) is used with widely differing meaning. In one restricted sense it refers to a systematic treatment of the logical and mathematical foundations of formal demography (102-3). At the other extreme it is sometimes used for a purely speculative treatment of population questions. In the past, studies of interrelations between demographic and other phenomena have necessarily tended to be somewhat speculative. There is now an increased emphasis on more objective interdisciplinary studies dealing with specific relations between the results of demographic investigations and the results obtained by other kinds of scientific inquiry. The theoretical treatment of population was largely centred in the past on the relationship between total population and resources 1, i.e., the means available to maintain the population, or production 2, the creation of goods and services.
Consideration of the relation between population and resources leads to the concepts of over-population 1 aud under-population 2. These terms are, of course, defined only at a given fixed level of development 3. There is said to be over-population when the elimination of a number of inhabitants would yield certain advantages to the remainder. Under-population, on the other hand, implies that such advantages would accrue from a rise in numbers. When neither an increase nor a decrease would yield advantages, there is said to be an optimum population 4, sometimes briefly called an optimum 4. The advantages yielded may be economic in character and in that case it is an economic optimum 5. The discussion of economic optima generally proceeds in terms of economic welfare but as this is difficult to ascertain empirically, the level of living 6 or standard of living 6 is sometimes substituted. This is approximated by the real national income per head 7, i.e., the total amount of goods and services produced in a particular period (or its equivalent in money income adjusted for variation in purchasing power) divided by the total population during the period.
- 5. Some writers have used the concept of a power optimum and a social optimum as well as of an economic optimum.
- 6. The expression "standard of living" is restricted by some economists to mean an accepted goal or recognized set of needs, as contrasted with the level of living actually attained. Others use these terms interchangeably.
- 7. The erroneous term per capita is sometimes used.
Recently economists have emphasized the dynamic relations between economic growth 1 or economic development 1 and rates of population growth and changes in population structure; they tend to use the concept of the optimum rate of change 2 of population, i. e., the rate of growth which will be consistent with the maximum rate of increase of the level of living. This problem is particularly acute in countries with a low level of living, which have come to be called under-developed 3 countries, where the relationship between population growth and economic well-being has been the subject of investigation.
The maximum population 1 of a territory, sometimes called its carrying capacity 1, is generally understood in an absolute sense to mean the largest number of persons that could be sustained under specified conditions; but it is sometimes used to denote the largest number that could be supported at an assumed standard of living. Conversely the minimum population 2 is generally taken to be the smallest number of persons in an area which is consistent with group survival 3.
The term population pressure 1 is used in a number of different senses. According to the Malthusian population theory 2 (101-4), so called after its originator, there will inevitably be pressure of population on the means of subsistence 3. Any change in the volume of available means of subsistence would generate population growth (701-1) until population equilibrium 4 would again be attained when the level of living had reached a subsistence level 5, i. e., a level just sufficient to maintain life. The equilibrium would be maintained by the elimination of any surplus population either through positive checks 6, sometimes known as Malthusian checks 6 (famine, pestilence and war), or through the preventive check 7 of moral restraint 8 consisting of postponement of marriage 9, coupled with abstinence from sexual relations before marriage.
- 7. The term preventive check in English is generally used only with reference to the doctrines of Malthus.
The term Malthusianism 1 denotes the doctrine that a check in the rate of population growth is desirable. Neo-Malthusianism 2, whilst accepting the desirability of checking population growth, advocates that such restriction should be achieved through the use of birth control methods (624-3).
- 1. Malthusianism n. — Malthusian n., one who accepts the doctrines of Malthus. The French term "malthusianisme" has acquired an extended meaning. It applies to any doctrine advocating a restriction in population growth, for whatever reason, and has even been used for economic restrictionism.
The process of transition from a situation in which both fertility and mortality were relatively high to one in which they are relatively low which has been observed in many countries, is sometimes called the demographic revolution 1 or vital revolution 1. It has been suggested that the process of industrialization tends to bring about a type of demographic change which is characterized by a fall in mortality, followed after a period of time by a fall in fertility, thus resulting in rapid population growth during the period of demographic transition 2. Economists have studied changes in productivity 3, i. e., in the production per member of the labour force, or per head of the population, associated with this transitional period.
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