Before discussing our fluid-like migrations, it is necessary to determine what is overcrowding. We will call a place saturated when it contains as many men as can be fed with food raised in that place. Here, again, population acts like a fluid. The soil cannot possibly hold all the rain poured upon it. Some must run off or be evaporated after collecting in pools, nor can the surface hold the rain of babies poured upon it. They, too, collect in pools of humanity to be evaporated by death, or they must flow off in migrating streams as soon as able.
The depth of these pools of humanity, or the density of population, depends chiefly upon the stage of civilization; that is, the saturation point rises with knowledge, just as the saturation of air with moisture rises with the temperature. The higher the culture, the more food can be produced from a given area, for cultivated land produces two thousand times as much food as an equal area of hunting land, and in the future it will produce still more. A country that could support one savage hunter for each fifty square miles, might support ten pastoral people, or a hundred semi-civilized agricultural and pastoral, or 1,600 to 2,000 modern farmers, or 3,000 farmers in a short time. Within a century German farmers have trebled the amount yielded per acre. Only recently we ourselves have learned of new methods of raising corn, so that one State alone added 45,000,000 bushels to her yield without increasing the acreage. It is predicted that these new discoveries will eventually add a billion bushels to our crop, and every year, at least in every decade, there is a discovery which increases the yield of some food.
The whole world seems to be at work on this one line of making it possible for more men to exist on earth. In the studies of cereal raising, the strides have been enormous in the last seventy-five years - probably more than in any previous thousand. Even in the matter of fruit trees, the trend is toward the dwarf varieties, which bear earlier and which can be replanted almost like cereals, and the yield per acre is enormously increased.
As an illustration of the manner in which the inventions of civilization increase the food supply of deserts, we need mention only one - the new varieties of spineless cactus (opuntias) created by Luther Burbank, of Santa Rosa, California. These are most valuable foods for live stock, and enable us to raise fodder from lands otherwise worthless. They are very rich in starch and the fruit in sugar. The plants are hardy and live without cultivation. He estimates that they will yield an average of ninety tons of forage per acre besides enormous amounts of fruit, which means, of course, an enormous addition to the world's population, for it utilizes arid, rocky and rough ground now wholly unproductive, in both hot and cold climates.
Irrigation is another means by which civilization increases the saturation point. Not only docs it cause the desert to yield foods, but to yield them in progressively increasing amounts. Even when there is plenty of water, the fertile lands are often so high that it requires great engineering skill to design dams and canals. Barbarous peoples, as in ancient Egypt, could irrigate only the flat lowlands at or near river deltas, but modern man is creeping slowly up-stream. Until the twentieth century our irrigated lands were solely the lowest valleys, but we are now taking in higher land. As the work requires government initiative, we ushered in the new century by the formation of "A Reclamation Service" as a part of the Geological Survey.
By 1906 this service had built seventy-seven miles of main canals, fifty-four miles of distributing canals and one hundred and eighty-six miles of ditches, besides necessary dams, roads and tunnels. It had started thirteen different schemes and planned about twenty-four more. It was calculated that the re-claimable area in the Great American Desert is 75,000,000 acres, costing one and one-half billions to irrigate, but valued at two and one-half billions when watered, and capable of giving homes to 7,500,000 farmers and food for some millions of factory hands. It increases our saturation point year by year, and as time goes on we will get water on still higher levels, so that it might be said that the saturation point will constantly rise but at a steadily decreasing rate.
Our possible increase of population, through irrigation, is much overestimated. Though nearly two-fifths of our area is arid - much of the western half - less than twenty per cent, of it is irrigable. Fifteen per cent, is mountainous, and sixty per cent, permanently arid. If we limit a family to ten acres it adds only 40,000,000 to the population. The stress is always so great that crowds await the opening of each new area. In two months in 1901, September and October, the railroads took out 30,000 colonists, of whom 5,000 were permanently settled, yet in five years only 10,000 found homes in the new irrigated areas. At a very liberal estimate each farmer requires two people to supply him with necessaries, so the total increase will be 120,000,000, but that is a long way in the future.
Canada is a brilliant illustration of the fact that increase of population depends upon increase of food and not on a profusion of babies. Louis XIV and his advisers tried in every way to increase the number of marriages and to stimulate the birth rate. Women were sent over by hundreds and thousands to be wives of the discharged soldiers previously sent out as colonists, and bounties were given for large families. Louis wanted population to increase of itself, for he said he needed his young men for the armies. All these measures failed, while New England, left to its own devises, and wholly abandoned by the mother country, increased by leaps and bounds. The causes are evident. Canada was based on the fur trade, for which agriculture was neglected. It could not support a large population and what it had was in the most abject poverty. In New England, all energies were directed to the production of food, and the population instantly responded. The birth rate was not as great as in Canada but the increase was far greater.