20 THE TREND OF THE RACE 



But while it is futile to argue over this question in the abstract, 

 it may become a very practical problem if it is narrowed down to 

 particular characteristics of a given breed under a specified range 

 of conditions. We may illustrate this by considering the effects 

 of heredity and environment in raising corn. Everyone knows 

 that corn grown on rich fertile soil produces a much greater yield 

 than corn grown on poor soil. Everyone knows also that, in a 

 given soil, the yield depends largely on the variety of corn that 

 is used for seed. There are varieties which in fair soil will yield 

 over ICO bushels per acre; others under the same condition which 

 produce only miserable nubbins yielding less than five bushels 

 per acre; and some, to take an extreme case, which would produce 

 no seed at all. We get a variation due to heredity between say 

 150 bushels per acre and o. If we take extreme environmental 

 conditions we get a variation in a given strain between the 

 maximum yield (say 200 bushels per acre) and o, for it is obvious 

 that if we planted our corn in an environment sufficiently unfa- 

 vorable it would not grow at all. There is no use arguing which is 

 the more important in raising com, good seed or good soil and 

 climate. If, however, we ask whether it is more important to 

 make the best choice of seed between variety A and variety B 

 or to make the best choice of one or the other of two pieces of 

 ground, our question is a sensible one and capable of fairly easy 

 solution. We may test our varieties under given conditions and 

 compare our yield. We could then obtain a measure of their 

 hereditary difference under a given constant environment, and 

 express it in a ratio such as A:B: 1^:4. Similarly we might test 

 out the yield of each variety in our two fields and we might find 

 that one field C is so much better than the other that both vari- 

 eties produce twice as much in the first as they did in the second. 

 If they continue to do so over a period of years varying with 

 temperature, rainfall, etc., we might say that for these particular 

 varieties of corn the relative influence of fields C and D is as 2:1. 

 Therefore we might conclude that the choice of a proper field is 

 more important than the choice of the best seed. If, however, it 

 was a question of the seed of variety B and the seed of variety C 



