OPTIMUM POPULATION. The origin of this term is not clear. Since the World War it has come into common use to indicate a conception of the relation between population and the produce of industry to which Prof. Edwin Cannan first gave clear expression. The optimum theory of population which is outlined in what follows was not held by Malthus or by the older authors who discussed the population problem. It was their failure to formulate this theory which robs their treatment of the matter of much of its value. This conception which lies at the basis of the position now taken by all authorities may be briefly expressed as follows. At any given time the population which can exist on a given extent of land, consistently with the attainment of the maximum return to industry possible at the time, is definite. In other words, for any given area of land under any given set of circumstances there is an optimum population. If population is at the optimum number the greatest return per head possible under the circumstances will be attained. Departure from the optimum, whether in the direction of deficiency or of excess, will be accom panied return per head less than the possible return. i Departure in the direction of deficiency is called under-population and i in the direction of excess is called over-population.
i It important to realize that no distinction is to be drawn between agriculture and manufacture in relation to this matter. In Prof. Cannan's words "if we start from what I have called the point of maximum return, we can say of manufacture as well as of agriculture that returns diminish as we move in either direction from that point." It is therefore essential from the point of view of economic prosperity that the population of any country should approach as closely as possible to the optimum. Over and under population alike imply a smaller income per head than could be attained with smaller and larger numbers respectively. Unf or tunately attempts to ascertain whether under- or over-population exist meet with the utmost difficulties. Unemployment is not necessarily an indication of over-population and the comparison of figures for the national income over a period of years is an uncertain guide. It is not possible to say whether or not England or the United States are over- or under-populated. It is, however, generally held that parts of India and China are probably over populated. It is in other words probably true that the inhabitants of these countries would be better off if the population was less dense. (See also POPULATION.)