Facts and Factors of Development 55 



7. Parallel Development of Body and Mind. The development 

 of all of these psychical faculties runs parallel with the develop- 

 ment of bodily structures and apparently the method of develop- 

 ment in the two cases is similar, viz., progressive differentiation 

 of complex and specialized structures and functions from relative- 

 ly simple and generalized beginnings. Indeed the entire organism, 

 structure and function, body and mind, is a unity, and the only 

 justification for dealing with these constituents of the organism 

 as if they were separate entities, whether they be regarded in 

 their adult condition or in the course of their development, is to 

 be found in the increased convenience and effectiveness of such 

 separate treatment. 



Development, like many other vital phenomena, may be con- 

 sidered from several different points of view, such as (i) physico- 

 chemical events involved, (2) physiological processes, (3) mor- 

 phological features, (4) ecological correlations and adaptations, 

 (5) psychological phenomena, (6) social and moral characteris- 

 tics. 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 belief that each of the succeeding aspects of devel- 

 opment named above may be causally explained in terms of the 

 preceding ones, and hence all be reducible to physics and chem- 

 istry. 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 development 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. 



The phenomena of mental development in man and other ani- 

 mals may be summarized as follows: 



