166 ORGANIC EVOLUTION CONSIDERED 



sibility arises from the occurrence in nature of a 

 principle which has been called the Correlation of 

 Growth." 



Thus correlation of growth is brought in as a sup- 

 plement to natural selection in attempting to account 

 for organs through their long functionless period. 

 It is evident that correlation of growth would cause 

 the propagation of any new parts that might arise, 

 and that a useless part would be preserved as readily 

 as a useful one. Siuce variations take place in all 

 sorts of directions, most of which could never be of 

 any use, we would, by this law, expect to find any 

 animal possessing a large number of parts that are 

 useless. Such, however, is not the case. The rule is 

 that useless parts are the rare exceptions. 



To rely upon correlation of growth to explain the 

 preservation of eyes, ears, legs, wings and other es- 

 sential organs through their incipient stages is far 

 beyond what the known facts warrant. 



It is admitted by most evolutionists that natural 

 selection alone is insufficient, and that it must be sup- 

 plemented in various ways. The supplement, how- 

 ever, sometimes becomes the principal thing, as in 

 the above case of correlation of growth to account for , 

 the origin and preservation of the most important 

 organs. 



Herbert Spencer, after showing " the inadequacy 

 of natural selection," explains such difficulties, al- 

 though he does not specify these organs, by referring 

 them to " a cause which it is now the fashion among 

 biologists to ignore or deny." "This cause is the in- 

 heritance of acquired characters." * He shows that 

 the sense of touch, as we find it in different parts of 

 the body, has not been developed by natural selection, 

 and he claims that " inheritance of acquired charac- 



* Popular Science Monthly, April, 1893. 



