24 Comparative Conceptions 



the further operation of natural selection upon the organ- 

 ism's functions. 



So we have certain comparative conceptions : variation 

 with natural selection, consciousness or intelligence with 

 plasticity, and accommodation by functional selection. 

 They are comparative in the sense which is now occupy- 

 ing us, that is, psychophysically ; since the meaning of any 

 one of them is not exhausted in its application to either 

 mind or body, without appeal also to the other of these 

 two psychophysical terms. 



For example, the meaning of the evolution of the brain 

 cortex, with the extreme plasticity which is its main char- 

 acter, through the entire Hne of mammalian descent, can 

 be understood only when we recognize the evolution of 

 intelligent endowment which accompanies it ; and the 

 method of the selective function of consciousness can only 

 be understood, in my opinion, in the light of the method 

 of survival by selection from overproduced variations, 

 which is the method of natural selection. 



§ 3. Correlation of CJiaractcrs 



Another highly interesting comparative conception is 

 that connoted by the biological term 'correlation.' ^ This 

 idea covers the fact that certain characters of the organ- 

 ism are correlated with, connected with, or in other regu- 

 lar ways related to, certain other characters, in such a way 

 that modifications or variations of the one are accom- 

 panied by changes in the other also. This is true, not 

 only of those characters in which it is difficult to deter- 

 mine the precise function, and of which, therefore, the 

 definition itself is difficult and uncertain, since it involves 



1 Sec instances given in Chap. XIV. §§ I-3. 



