36 IOWA ACADEMY OF SCIENCES. 



the same environment. It should here be particularly 

 noted, however, that in the same environment there w^ould 

 be no progressive adaptation under the influence of this 

 factor alone; each generation would be modified to the 

 same degree as the first that found itself in the new 

 environment. Nevertheless, large numbers of individuals 

 would be protected from extermination for successive 

 generations and so full opportunity given for favorable 

 fortuitous congenital variations to arise, which would be 

 perpetuated by selection. To be favorable, such variations 

 would be in the same direction as the acquired characters, 

 although not in any sense caused by them. In the words 

 of Conn, in a review of the theory, "The chief significance 

 of this theory, then, is that it greatly prolongs the time 

 over which the race might wait for the appearance of 

 proper congenital variations." 



For some time it has seemed to me that I could perceive 

 another method of evolution, similar in many features to 

 orthoplasy, which would still further harmonize some of 

 the apparently opposing views of Neo-Lamarckians and 

 Neo-Darwinians. 



It appears to me that insufficient emphasis has been 

 placed on the variation in the ability of different individ- 

 uals to respond to new stimuli, that is to changes in the 

 environment. AVhen a number of individuals are sub- 

 jected to new conditions, implying increased stimuli to 

 certain parts, either by increased use or the direct influ- 

 ence of the environment, it is impossible to predict how 

 much change will occur in the different individuals; but 

 certain it is that they will differ very much in this respect. 

 Some domestic animals respond feebly to better care, 

 others strongly; put a number of boys through a gymna- 

 sium course, and while the muscles of all may be much 

 developed at the end, the differences are usually startling; 

 send two children of the same parents to the same school, 

 and have one come out with a keenly developed intellect, 

 the other mediocre. 



Now, I believe such variations will be the most numer- 

 ous, and greatest in degree, when tJtere is a need of tiew 



