earlier volume of the Monthly (November, 1900) President Henry S. Pritchett predicted, a population of over a billion two hundred years hence and of about twelve billion six hundred years hence. We may agree with Professor Brigham that "population is a vast and wandering theme." It is, however, fascinating and not without practical interest. Emigration laws and even birth rates are not unaffected by such guesses as may be made.
The population of a country is in the main limited by the food supply. Man does not live by bread alone, but his higher needs are increasingly supplied by an increasing population. With a given stock and a given environment the-number of men of genius who add to the social heritage is proportional to the population. Material supplies other than food are needed, but they are not likely to become exhausted. Metals and clays are inexhaustible; the increasing difficulty of obtaining them will surely be met by improved methods. Metals—also wood and even the materials of clothing—can be used over and over again should this become desirable. Fuel, like food, is consumed, but the sun's energy is boundless and means are already at hand to obtain all that may be needed. It is safe to say that the population of the earth is limited only by its food supply.
The area of continental United States apart from Alaska is, in round numbers, two billion acres, of which one half is in farm lands and one fourth under cultivation. Probably three fourths of the total area could be brought under intensive cultivation and made to give fifty bushels of corn per acre or its equivalent. The food value of a bushel of corn is sufficient to support a man for nearly a month, and the product of an acre would about support four men for one year. If one half of the grain were turned into animal food for human consumption, two men per acre could be fed and the country would support a population of 3,000,000,000. Apart from the possible synthetic manufacture of food, it may be regarded as probable that improved agricultural methods will in the course of a century double the present maximum productivity. It should also be remembered that tropical lands are far more productive and under an ideal civilization would export food and import manufactures. The maximum population that might be supported in the United States may, a century hence, consequently be placed at about ten billions.
Such a maximum figure compares with a probable figure somewhat as the theoretically possible efficiency of a steam engine compares with its actual efficiency. But a population of one billion could be supported comfortably. Our present food supply feeds about a hundred million. Better methods would double the production from the area at present under cultivation and less wasteful methods would halve the consumption. If the area under cultivation were increased from 25 per cent, to 62.5 per cent, there would be food for a billion people. Allowing for a reasonable exchange with tropical countries and an ever increasing efficiency in production such a population would have an ample food supply with a reasonable amount of meat and fruit and even as much alcohol, tobacco and coffee as may be desirable for health. Such a population would not mean in any sense living under the conditions of the Asiatics. The more dense the population within the limits stated, the greater would be the per capita wealth. Nor will the country be crowded. Doubtless most of the people would prefer to live in villages or cities and for the quarter that might prefer the country there would be thirty acres for each family. What the actual population of the United States will be a hundred years hence is a very different question. In a state of nature the number of a species may be reduced by enemies or disease, but as a rule they are limited only by the food supply. But with
