310 



The Journal of Heredity 



Now, if it is ^oing to be necessary for 

 us to practice some degree of rational 

 selection, we must be svire that it is 

 rational — it must be based upon positive 

 knowledge. What has modern bio- 

 logical research to ofifer in the way of 

 contribution to such knowledge '1 In the 

 first place we can readily see that a large 

 part of the disagreement which has been 

 mentioned is due to difference in opinion 

 as to the influence which the environ- 

 ment ma\' have on the individual and 

 on the oflfspring. It is the old question 

 of Nature and Nurture. While I am 

 free to admit that in its abstruse aspects 

 this is one of the most dif^cult questions 

 confronting the biologist, I believe that 

 much unnecessary confusion and need- 

 less discussion has resulted from the 

 tendency of writers to exaggerate their 

 \'iews either on the one side or the 

 other, and not to accord the question 

 fair treatment. When I am asked, as 

 often hapjjens, which I consider of 

 greater importance, heredity or en- 

 vironment, I commonly give a Yankee 

 reply by asking in return. Which is of 

 more importance for sustaining life, 

 food or air? 



INFLUENCE OF ENVIRONMENT. 



Although we may concede what is 

 the almost universal biological ojjinion 

 of today, that the effects of environment 

 arc not in the crude sense heritable, we 

 must not, nevertheless, lose sight of the 

 fact that the environment is a most 

 injxjrtant determining factor in evo- 

 lution and in selection. This may 

 jjcrhaps best be illustrated by an 

 example. Let us supjxjse two cows, 

 one of which is inherently a low pro- 

 ducer, and is incaj^able of producing any 

 considerable quantity of milk beyond 

 that necessary to raise her calf. The 

 other, on the other hand, has inherited 

 the capacity to jjroduce a large quantity 

 (jf milk under certain conditions, namely 

 projjcr feeding, care and handling. Now 

 let us first consider these animals under, 

 say, range conditions, where they re- 

 ceive no special care, and where they 

 have to hustle for their own mainte- 

 nance. So far as milk production is 

 concerned they will measure up about 



the same — each will produce enough to* 

 raise her calf and no more — and very 

 likely the inherently low-producer will be 

 at an advantage under these more 

 severe conditions. But now take the 

 two animals and ]jlace them in a modern 

 dairy with scientifically jjrcpared rations, 

 and the best treatment that modem 

 dairy practice can provide. What is 

 the result '1 The animal which inherited 

 the capacit}' to respond to such treat- 

 ment does respond at once by a sus- 

 tained increase in the flow of milk; but 

 the other does not. The former was 

 hampered by conditions in the first 

 place, but the latter is now absolutely 

 prevented by her nature from the 

 possibility of a response to the improved 

 conditions. We see therefore that these 

 conditi(«is were necessary to make 

 apparent the differences which existed 

 in the hereditary make-up of the twO' 

 animals. Is not the same true of the 

 human race? It is only by giving 

 opportunity to all, that we may know 

 which are capable of profiting by that 

 opportunity. The good environment- 

 then is necessary for differentiation, and 

 without differentiation how may we 

 hope to make selection' 



Two other biological concepts are of 

 importance. These have grown out of 

 recent Mendelian investigations. The 

 first is the idea of hypothetical factors, 

 which are definite heritable units, and 

 upon the presence of one or more of 

 which all the characters of an organism 

 depend. Since the factors beha\'e for 

 the most part inde])endently in in- 

 heritance, the ])robleni of handling them 

 in selection becomes an extremely com- 

 l)lex one. Where only two factors are 

 concerned, any desired combination as 

 to their presence or absence may be 

 expected in at least one of sixteen 

 individuals in the second generation. 

 But as the number of factors to be dealt 

 with increases, the number of indi- 

 viduals necessary to give all the com- 

 binations increases at a most dispro- 

 1)ortionate rate, as is indicated in the 

 following table, which shows the number 

 of individuals which according to ex- 

 pectation would be necessary to pro- 

 duce at least one individual with each 



