1 1 8 A Factor in Evolution 



selected. We have seen how it may be done by a certain 

 competition of functions with survival of the fittest among 

 them. But this illustrates the idea of natural selection. I 

 do not see how Henslow, for example, can maintain- -apart 

 from ' special creation ' the so-called ' self-adaptations ' 

 which justify an attack on natural selection. Even plants 

 must grow in determinate or ' select ' directions in order 

 to live, and their reactions are responses to stimulations 







from the environment. 



4. So we may say, finally, that plasticity, while itself 

 probably a congenital variation or an original endow- 

 ment, works to secure new qualifications for the creature's 

 survival, and its very working proceeds by securing a new 

 application of the principle of natural selection to the pos- 

 sible modifications which the organism is capable of under- 

 going. Romanes says : ' It is impossible that heredity can 

 have provided in advance for innovations upon or altera- 

 tions in its own machinery during the lifetime of a partic- 

 ular individual.' To this we are obliged to reply in sum- 

 ming up as I have done in another place: we reach 

 'just the state of things which Romanes declares impos- 

 sible- -heredity providing for the modification of its own 

 machinery. Heredity not only leaves the future free for 

 modifications, it also provides a method of life in the 

 operation of which modifications are bound to come.' 



8. Terminology 



In the matter of terminology some criticism is to be 

 expected from the fact that several new terms have been 

 used in this paper. Indeed, certain of these terms have 

 already been criticised. It seems, however, that some 



