198 THE PROBLEMS OF EVOLUTION 



must be met within this latitude of response if 

 the individual is to persist, and the most extreme 

 change that can be expected is an adjustment of 

 the function in the direction of the environmental 

 demand, not a sudden complete shift to an en- 

 tirely new response. An opportunity may be 

 extended of which, if it has the power, the organ- 

 ism may take advantage. The results in evolution 

 must necessarily be slow, perhaps too slow to be- 

 come evident as a true evolutionary change within 

 a reasonable span of experimental study, but this 

 is clearly the direction which our investigations 

 must take. 



If this procedure should ultimately demonstrate 

 that organisms still have some capacity for evolu- 

 tion, that they may still meet new environmental 

 conditions and become adjusted to them as species 

 by an actual change in the heritage, then all of the 

 significant facts and observations relating to evo- 

 lution would be harmonized. The process would 

 not be Lamarckian, for the environment would 

 not have impressed itself upon the organism and 

 organic responses would not be wholly adaptive. 

 It would not be Darwinian, for the organism would 

 actually be undergoing change in direct response 

 to the environment, and it would not be muta- 

 tional, for it would involve a gradual building up 

 of a character in the heritage under the proper 

 environmental stimulus. Yet it would be all of 



