No. 602] 



THE SELECTION PROBLEM 



75 



from which they come. Here is real selection making 

 real evolutionary progress, because its point of applica- 

 tion is the germ and not the soma. That the same agent 

 may produce an evolutionary change in the opposite 

 direction in another organism, the guinea pig, as has been 

 shown by Stockard^*' to be the case, seems to mean, from 

 the point of view of the present discussion, nothing more 

 than that the direction and amount of any evolutionary 

 change is, fundamentally, a function of two variables, the 

 organism and the environment. If the same environ- 

 mental stress produced the same evolutionary effect upon 

 all organisms, then it would follow that all organisms in 

 the same environment must necessarily be alike at the 

 end of the process, which is, of course, not the case. 



II. The Expeeience of Pkactical Bkeeders 

 Let us at this point leave our discussion of natural 

 selection and turn to the other great aspect of the prob- 

 lem, artificial selection. Here we shall tread on surer 

 ground, first, because it is where the great bulk of the 

 experimental work on the selection problem has been con- 

 centrated, and second, because^ the considerable mass of 

 reliable historical material about the origin and improve- 

 ment of domestic animals and plants be€omes available 

 as a source of pertinent and critical evidence on the prob- 

 lem. At the outstart it may be recalled that it was on the 

 supposed results of artificial selection, as set forth in the 

 experience of practical breeders, that Darwin chiefly re- 

 lied for objective evidence in favor of natural selection. 



In general this evidence has been accepted very un- 

 critically by followers of Darwin. This is not strange in 

 view of tlie fact that there have been, and are now, rela- 

 tively few trained l>i(^loo-ists who know anything at first 

 hand about the ii]-actieal breeding of animals for the show 

 I'ing, advanced registry test, or any other purpose which 

 involves nect^ssarily the production of elite specimens 

 which shall rank measurably with the best of the breed. 



26 Cf. Stockara, C. E., and Papanicolaou, G., Amer. Xat.. Vol. 50, pp. 

 65-88, 144-177. 1916. 



