326 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1957 



there is no incentive to increase soil fertility, though there is a need 

 for the whole community to organize itself so that a minimum level of 

 soil fertility is maintained. This need is the basis of the tribal organi- 

 zation of many primitive societies living by nomadic, shifting culti- 

 vation which allows the soil to rest and recuperate between short 

 periods of cultivation. It was also the basis of the three-field system 

 of communal agriculture which maintained soil fertility in feudal 

 England or, rather, slowed down the inevitable soil exhaustion that 

 had to accompany social evolution. In these predominantly agricul- 

 tural stages of human societies Man is a consumer of soil fertility. 

 He cannot help it, any more than a young forest can help taking more 

 out of the soil than it gives back ; he cannot help it even when he is 

 armed with all the wisdom which past experience and twentieth- 

 century science can give him — because it is part of the nature of 

 economic Man. 



It seems also to be the nature of part of economic Man to congregate 

 in towns at a certain stage of his social development, and to abandon 

 agriculture for more profitable pursuits. The growth of towns has 

 a powerful effect on soil evolution. Towns create far more, and more 

 concentrated, wealth than agriculture can create, a rising standard of 

 living, and a greater demand for the produce of the soil. A small, but 

 very significant, fraction of this town-made wealth flows back into the 

 country, and the towns' demands for food, clothing, and, nowadays, 

 the agricultural raw materials of industry make it profitable for 

 farmers to produce as much as they can from their land. To begin 

 with, this results in an accelerated exhaustion of the soil, but if the 

 towns continue to grow in size and prosperity a stage is reached — 

 and has been reached in every successful civilization — when it pays 

 the farmers to intensify production, to increase output per acre and, 

 therefore, to raise soil fertility. If it pays Man to increase soil 

 fertility, he does it. That, I think, is the basic natural law governing 

 the growth and survival of civilization. 



A good example of the initial fertility-destroying and subsequent 

 fertility-making influence of towns is afforded by the recent history 

 of the United States. The drain on soil fertility to satisfy the 

 demands of British towns for cheap food in the last century was one 

 cause of the terrifying soil erosion which has afflicted the United 

 States. But very recently a small part of the immense wealth pro- 

 duced by American industry has begun to flow back into the soil. 

 Farmers are finding that it pays to conserve their soil and to raise 

 its fertility. Soil fertility, measured by crop yields, is rising more 

 rapidly in the United States than in any other part of the world. 



Towns increase a country's soil fertility by enabling farmers to 

 afford to put more into the soil than they take out of it. Fertility 



