creased wealth is sufficient to support a larger population at the accepted standards. This was the case in Germany previous to 1900, when the death rate declined more rapidly than the birth rate. During a transition period of this kind the decline in the birth rate lags behind the decline in the death rate because standards of living change slowly.

The Law of the Increase of Population. The conclusion reached from the discussions of the birth rates and the death rates may now be combined into a general statement of the law of population growth. The numbers of the human race, like those of other species of life, depend upon the environment. If conditions of life are easy, population will increase rapidly until conditions become more difficult, when the rate of increase will be lessened through the action of the environment. If the restricting force is the physical environment, population will be limited chiefly by a high death rate. If the restricting force is the social environment, population will be limited chiefly by a low birth rate.

A more specific statement regarding the action of the physical and the social environments cannot be made for the total population, because society is not a unit but is composed of different groups influenced by different motives. That part of the population influenced chiefly by the physical desires will tend to multiply more rapidly than the food supply and their numbers will be held in check by a high death rate. That part of the population influenced by the desire for approbation will limit their numbers to conform to their social positions. That part of the population influenced by cultural desires will also limit the number of births; but the limitation will be determined here by the nature of their work and their powers of achievement rather than by definite standards of living, hence the birth rate among them will be more variable.

Among the many possible measurements of the advance of civilization one would be the character of the dominant motives. Civilization advances as the social and cultural springs of action dominate over the physical; and one of the most important results of this psychological change has been the conscious regulation of population in accordance with social conditions. Thus far the exercise of reason in the regulation of population has applied to a part of society only and hence a single law of population cannot apply to society as a whole and explain all existing phenomena.

REFERENCES FOR COLLATERAL READING METCHNIKOFF, E., The Prolongation of Life. MINOT, C. S., Age, Growth, and Death. PEARL, R., The Biology of Death, The Scientific Monthly, Feb-Sept.

1921. SHALER, N. S., The Individual, Ch. 3. WEISMANN, A., The Duration of Life, in Essays upon Heredity.

CHAPTER XXI

MIGRATIONS

Migrations will in this chapter be discussed only so far as they affect the numbers and character of populations. The causes of migrations are usually economic, political, or religious; but, in their effects upon population, the causes are of less importance than are the characteristics of the peoples migrating. Such points as the size of a migrating group, - that is, whether it consists of a large band, family group, or isolated individuals, -economic status of the migrants, their ages, sex, and conjugal condition, would all influence in turn the size and character of the populations concerned in the movement.

When migrations assume considerable proportions they affect the country which the migrants leave, — which we may call

the emigrating country, - as well as the country to which they go, - the immigrating country. The effect on the immigrating country will be considered first.

Effects of Immigration. People migrate to two types of countries and with quite different results. They may go to a new, partly settled country, in which there is still plenty of free land; or they may go to a country which is already well settled, where competition is keen and class distinctions are in evidence.

The effect of a migration on a country of the first class is comparatively simple, and may be readily deduced from the general laws of population already given. As has been shown, a population under easy conditions of life will increase rapidly by an excess of births over deaths until the conditions of life become more difficult, when the rate of increase will be checked. Therefore the migration of peoples to a district where the conditions of life are still easy will populate that district more rapidly than would otherwise be the case and will hasten the advent of that struggle for life which brings its own automatic check on the natural increase of peoples.

When people migrate to a country which is already well settled the results are more complicated and depend upon the economic class to which the migrants belong, - that is, whether they belong to the highest, the middle, or the lowest class in society.

When immigrants belong to the highest class. Immigrants form the highest class in a country when they come as a conquering people to settle in the territory of the conquered. Such migrants will usually form a large compact body and will evolve a more complex social life than the native population and will probably soon tend to multiply less rapidly and therefore become a smaller and smaller proportion of the total population. Whether or not they multiply less rapidly than the native population, their final assimilation is almost certain. In a conquering people males usually predominate and they marry native women; and, provided no caste distinctions are maintained, the native population being much the larger finally absorbs the conquerors. This was the fate of the Gothic invaders of Italy and of the Norman conquerors in England. If invaders wish to preserve their racial identity they must form a closed caste as a measure of racial defence, for a caste protects them from intermarriage and also from economic competition with the native population. The successive conquerors of India retained their identities by this method, as did also apparently the Incas of Peru.

When immigrants belong to the lowest class. That type of migration where the immigrants belong to the lowest class finds its best illustration in the modern movement from Europe to the United States. When such a movement is as large as this one has been in recent years, the migrants become a disturbing factor in the process of adaptation. According to the principles already stated in a previous chapter, a given population undisturbed by outside forces adapts its birth and death rates to its economic environment and standards of living. But a considerable addition of immigrants to the lowest class will make the struggle for life much more intense, thus altering the economic environment. Now a change in the environment must also change either standards of living, or rates of multiplication, or both. That class in the population which has no special standard of comfort to maintain will show the effect of the excessive competition in a lower standard of living, indicated both by increased poverty and a higher rate of mortality, especially among infants. That class in the population which has acquired standards of comfort will show the effects of the increased competition by a lower marriage or birth rate, for it will not easily abandon its standard of living. The middle class, as well as the upper stratum of the lowest class, will be affected, and the results will be especially noticeable in the rising generation. The immigrants themselves may not become identified with the middle class, but they are likely nevertheless to compete with them either directly or indirectly and to render their position less secure.

This effect of extensive immigration on the birth rate has been felt in the United States, and is obvious in the birth rates for native and foreign born in Massachusetts and New Hampshire already presented, but the effect of increasing competition on the birth rate is shown more fully in the figures given by the United States Immigration Commission which investigated birth rates by nationalities in selected districts of the United States,

the state of Rhode Island and the cities of Cleveland and Minneapolis being chosen for urban rates, and 41 counties in Ohio and 21 counties in Minnesota for rural rates. The results are in complete accord with the theory of population here given. The birth rate of the native population was much lower than that of the foreign born. The rural birth rate was higher for both native and foreign born than the urban, although the most recent foreign immigrants showed the least difference in this comparison. And finally the birth rate of the native born of foreign parentage held a position intermediate between that of the native and that of the foreign born. The significant points in these statistics are that the newest immigrants belonging to the lowest economic stratum show the least tendency to

1 See Reports of Immigration Commission, Vol. 28, and Jenks and Lauck, The Immigration Problem, pp. 58–61.