THE PROGRESS OF SCIENCE 



435 



earlier volume of the Monthly (No- 

 vember, 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 Pro- 

 fessor 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 con- 

 sumed, but the sun's energy is bound- 

 less 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 ani- 

 mal 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 maxi- 

 mum productivity. It should also be 

 remembered that tropical lands are far 

 more productive and under an ideal 

 civilization would export food and im- 

 port 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 ac- 

 tual efficiency. But a population of 

 one billion could be supported com- 

 fortably. Our present food supply 

 feeds about a hundred million. Better 

 methods would double the production 

 from the area at present under cultiva- 

 tion 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 alco- 

 hol, tobacco and coffee as may be de- 

 sirable 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 



