§ 5. Birth rates. The increasing population has not been due to any general increase in the birth rate. In most coun tries where there are any records it has been decreasing, and in some cases more rapidly than has the death rate. The world's birth rate in 1911 is estimated to be 36.5 per thousand of population; that of the more advanced industrial coun tries is much less. In the quarter century between 1886 and 1912 the birth rate decreased in certain countries as follows: § 6. Death rates. A general decrease of the death rate makes possible a growth of population even with a decreas ing birth rate. The food production has been increasing and famines have been decreasing, while great improvements in medical and in sanitary science have at the same time been made. The death rate in a community is a rough index of its general welfare : the death of a large proportion of the children before they arrive at maturity indicates poverty or ignorance. The urban death rate in Europe in the Middle Ages was tremendously high, but during the nineteenth cen tury, as a result of engineering and sanitary progress, it sank nearly to that of the country districts. The race of man, ever since the beginnings of volitional control, has had a smaller death rate relative to the total number of individuals coming into existence than has any other species of living creatures. Even in the most miserable industrial population where one half the children die before they are five years old, the death rate is much less than among the young of the lion or the eagle. The average human death rate became much less in the nineteenth century than it had ever been before. The death rate in the world as a whole in 1911 is estimated to be 28.9 per thousand, which is far greater than that of the more advanced countries. The decrease in a guar ter of a century in certain countries is as follows (for com parison with preceding table) : The estimates of world population indicate that the increase of numbers was at the greatest rate in the half century from 1830 to 1880 and that it is now much less. Population in creased so rapidly that the limit of resources began to be felt. The pressure of population makes itself felt in various ways, and on various levels of national culture in Japan, India, Germany, the United States, and in almost all other lands.
§ 7. Population growth and intensive cultivation. Let us analyze the process of change when population is a dy namic factor. A growth of numbers disturbs an established equilibrium of cultivation on the extensive and intensive mar gins (see Chapter 12), changes the relation of the value of labor-services to land uses (and to all instrumental uses), and leads to new levels of adjustment. Real changes are, of course, always complex, and along with population-changes go changes in machinery, area, methods, use of fertilizers, etc. Our question is as to the effect of population-change in itself considered, other things being equal, and for simplicity is limited here to the case of staple food crops.
A population on an area varying in fertility would apply its labor to the best tract. This, in an earlier example (Chap ter 15) would be A, where, by hypothesis, 10 days' labor produces 24 units. Wages would stand at the level of 2.4 bushels and rents would be nil. When the pressure of popu lation requires that B should be cultivated, the wages on A would be 22 bushels and rent about 2 bushels. When culti vation moves to tracts C and D, rent arises successively on B and C. If each tract continued to be cultivated with the
same amount of labor as before, the rent on A would be first 2, then 4, then 6 bushels when tract D first came under cul tivation; the rent on B would then be 4 bushels, and the rent on C, 2 bushels. (See Figure 59.) But with each extension of the margin of cultivation there should occur increasing intensity of cultivation on the older tracts, so that the return to a unit of labor should be equal in the two uses. When labor will yield but 2.2 bushels on B, it will be applied on A as long as it yields as much as 2.2 bushels (not 2.4 as before). Then this would work out as to rents and wages (in bushels) as shown in the table. (The amount of increase of labor for intenser cultivation is arbitrarily assumed. It would vary in practice but always be more intense as cultivation extended.) So far as the rent results from differences in fertility, it depends on the maintenance of the fertility. If the fertile qualities of the better fields are not restored and maintained, the yield on the once better land would fall at the same time that cultivation extended to the poorer land. Rent may, however, in some cases result from mere advantage of location as population extends.
When a change in the relative quantity of land (or other agents) occurs that imputes to labor less bountiful results, it is a case of decreasing returns; a change in the opposite direc tion (through discovery, opening of new lands, increase of agents, etc.) is a case of increasing returns.
§ 8. Law of increasing and decreasing returns. The law of increasing and decreasing (or diminished) returns may be thus stated. The amount attributable to the labor element of a whole population varies with the amount and efficiency of the material agents at the disposal of labor, increasing if they increase more rapidly than population, and decreasing if the population increases more rapidly than they do. It is one aspect of the law of proportionality as applied, not to a private enterprise, but to the relation of the whole population to its resources. The law of decreasing re turns received a name first, and the term has been loosely ap plied to many very difficult problems.° It was first used in England about 1815 with reference to land in agriculture un der steadily increasing intensity of cultivation of the soil year s See note at end of chapter on Various meanings of diminishing re turns.
by year in order to get more food per acre. It was called the law of "the decreasing returns of capital and labor as applied to land." The course of events in England called attention to the subject. Population was growing rapidly, and there was need for more food. During much of the time from 1793 to 1815 England was at war, and it was hard to obtain food from abroad. The English farmers, tempted by the higher prices, took poorer lands (marshy, cold clay, infer tile) into cultivation and sought to get larger crops from the older fields. This took more labor per acre, and yielded a larger total product, but less per day's labor. Grain and other produce rose in price, land rents and land values in creased, wages fell, and therefore the peasant's day of labor bought less food than before. The worst period of all for high wheat prices was from 1800 to 1813; the year of highest recorded annual average price was 1812, $3.80 a bushel. It was a lesson in dynamic economics on a large scale.