2 Psychophysical Evolution 



special problem is to determine what sort of a theory of 

 biological evolution is rendered the more probable, when 

 we recognize, together with all the established biological 

 facts and principles, also the principles and facts of the 

 mental life which as psychologists we are bound to 

 accept. In the earlier volumes, we have 'read up,' so 

 to speak, from the individual to his species and to his 

 social group, considered as being also psychological ; now 

 we * read down ' from the individual, considered as an 

 organism, to the simpler forms from which he has had 

 his origin — all taken together as constituting an organic 

 whole having a natural history upon the earth. 



Looked at in this way, the papers which follow are 

 seen to have the unity of a common purpose, despite the 

 gaps in the presentation of the evolution problem as a 

 whole. They may be treated as each dealing with a 

 narrower question, yet as having reference to the larger 

 problem which may be called psychophysical evolution — 

 the evolution of mind and body together. As thus falhng 

 into certain groups, the discussions may be classed under 

 the general headings given to the main divisions or Parts 

 of the volume: I., the problem of Genesis as such — some 

 of its main illustrations and data; II., that of the Method 

 of Evolution — involving the determination of the move- 

 ment, its direction, and the results in which the genetic 

 factors, taken together, actually issue ; and finally III., 

 that of Criticism or Interpretation — of finding out the 

 limits, tendencies, termini, and in general the competence 

 of the genetic method in the court of science and philoso- 

 phy. Genesis, Method, and Interpretation may be taken 

 as the catchwords of such a series of papers whose com- 

 mon motive is covered by the words * Development * and 



