82 HEREDITY AND ENVIRONMENT 



chemical events involved, (2) physiological 

 processes, (3) morphological features, (4) 

 ecological correlations and adaptations, (5) 

 psychological phenomena, (6) social and 

 moral characteristics. All of these phases of 

 development are correlated, indeed they are 

 parts of one general process, and a complete 

 account of this process must include them all. 

 General considerations may lead us to the be- 

 lief that each of the succeeding aspects of de- 

 velopment named above may be causally ex- 

 plained in terms of the preceding ones, and 

 hence all be reducible to physics and chemistry. 

 But this is not now demonstrable and may 

 not be true. Function and structure may be 

 related causally, or they may be two aspects 

 of one substance. The same is true of body 

 and mind or of matter and energy. But even 

 if each of these different phases in the develop- 

 ment of personality may not be causally ex- 

 plained by the preceding ones, at least the 

 principle of explanation employed for any 

 aspect of development ought to be consistent 

 and harmonious with that employed for any 

 other aspect. 



