THE ORGANIC TENDENCY 199 



these together, for Lamarck recognized the activ- 

 ity of the organism in evolution, Darwin beUeved 

 in the potency of use and disuse as sources of 

 change, and any change in the heritage fits the 

 modern definition of mutations. Under these con- 

 ditions the biological world would be forced to 

 recognize the necessity which Whitman pointed 

 out thirty-five years ago and which I have sought 

 to emphasize in these pages, that it is not a ques- 

 tion of finding the potent factor in evolution, but 

 of learning how the obvious factors interact.^ 



But, as in so many biological problems, experi- 

 ment is necessary before this discussion can be 

 extended beyond a summary of the pertinent facts 

 and the apparent possibilities of evolution. We 

 know little or nothing of several of the most sig- 

 nificant questions involved, including the nature 

 of individual response, its possible effect on the 

 heritage, and its importance in connection with 

 such other evolutionary processes as preadapta- 

 tion and selection. It is completely illogical to 

 abandon this field of investigation without ade- 

 quate reason, or to deny its importance in the study 

 of evolution. It is the one field in which our knowl- 

 edge is at such an unsatisfactory point that we 

 can say neither "true" nor "untrue." We may 

 call it the inheritance of acquired characters and 

 arbitrarily discard it through the prejudices of the 



' Whitman, C. O., Woods Hole Biol. Lect, 1894, 1895. 



