OUR FUTURE COURSE 221 



result, but probably at such a slow rate that it 

 may not be experimentally demonstrable except 

 in very favorable cases. It is much more probable 

 that an induced change, if it can be brought into 

 relationship with other factors of the environment 

 than those which caused it to appear, may be fixed 

 in the species through experiments of suflScient 

 duration to afford convincing evidence of its im- 

 portance in evolution. The relation of such char- 

 acters to selective processes is a more delicate 

 matter, since any selection makes it necessary 

 to distinguish carefully between the heritage and 

 the somatic characters as the basis for selection. 

 The relationship is a valid field of inquiry in the 

 general process of evolution, but a dangerous one 

 for the study of acquired characters. 



The limited duration of experiments in this field 

 has been a necessity which will probably continue 

 to be felt. It has been possible to follow organisms 

 of short life through many generations, and for 

 this reason they are desirable material, but un- 

 fortunately experimental material must be sought 

 among species which show some capacity for varied 

 response to environment, whether or not their 

 other characteristics are favorable. Duration is 

 certainly an important factor in evolution, but it 

 may not be an unavoidable obstacle. Certainly 

 we cannot expect to work important changes in a 

 species in a few generations when individuals may 



