352 



TRANSMISSION 



more nearly in harmony with the environment, and this cumu- 

 lative influence, constantly exerted, generation after genera- 

 tion, slowly but surely modifies the race in the direction of the 

 environment, giving again the appearance of inherited modifica- 

 tions. Now in nature this selective influence is always at work, 

 sometimes by actually destroying the less adaptive individuals, 

 more often by affecting not life, but fertility or longevity, or 

 both, through little-noticed but insidious agencies. 



This is, moreover, the most powerful of all the means by 

 which environment influences species. It entirely outstrips the 

 results of direct influences upon individuals, and is fully able 

 to account for all ordinary cases of environmental influence. 1 



The source of the difficulty. Here is an ever-present, all- 

 powerful influence, bending species into harmony with their en- 

 vironment, and its effects must be fully eliminated or accounted 

 for before we can determine whether a residue remains to be 

 attributed to direct transmission. This is the source of the 

 greatest difficulty in attempting to learn whether modifications 

 are directly transmitted. 



This selective process of the environment results in the indi- 

 rect transmission of such modifications as increase the chances 

 of the individual in the struggle for existence; but what farmers 

 want to know is whether modifications produced by the con- 

 ditions of life are directly transmitted as such, independently 

 of the question whether they increase or decrease the chances 

 of life in the individual, and independently of all questions of 

 selection. 



1 The individual and the type. The student must be clear as to what consti- 

 tutes type. Every individual must be considered with reference to at least two 

 generations, the one to which it belongs and the next. The type of a race at any 

 particular moment is fixed by the personal qualities of //its adult members, and 

 for this purpose all individuals are of equal weight, and one character or differ- 

 ence is as good as another. Everything counts in fixing the type of an existing 

 generation. 



But when the next generation is considered, it is not so. Only those individuals 

 count which succeed in reproducing, and only those differences count that are 

 transmissible. The initial or natural type, therefore, as secured by transmission, 

 is somewhat different in succeeding generations, nor is it ever fully expressed in 

 adult members. The existing and visible type of any race is, therefore, at best 

 but an incomplete expression of its possibilities. 



