4 Psychophysical Evolution 



Looked at in this way, the problem as a whole — that 

 of Psychophysical Evolution — requires some preliminary 

 dissection. Certain distinctions are quite essential, the 

 more because, if they are too often neglected by biologists 

 and psychologists ahke, it is no doubt partly because they 

 are dealing respectively with the biological or the psycho- 

 logical, not with both. The first of these distinctions 

 is that between the two general provinces of research, 

 Biology and Psychology. 



§ 2. The Psychological and the Biological 



By the psychological I mean the mental of any grade, 

 viewed from the outside ; that is, viewed as a definite set or 

 series of phenomena in a consciousness, recognized as 

 facts and as * worth while ' as any other facts in nature. 

 The phrase * natural knowledge ' includes knowledge of 

 psychological facts in just the same sense as that of bio- 

 logical or chemical facts. The occurrence of a psycho- 

 logical change in an animal is a fact in the same sense 

 that the animal's process of digestion is. And the genetic 

 explanations which we find it possible to offer, in this case 

 or that, may draw upon facts of psychology, no less than 

 upon facts of biology. In the case, for example, of one 

 animal's recognizing another and being led by this recog- 

 nition to carry out the act of mating, we have a complex 

 series of events involving the psychological process of 

 recognition, joined with that of mating in the production 

 of one of the great results of nature, and illustrating one 

 of the principles important to the last degree for the 

 theory of evolution — the principle of hereditary resem- 

 blance. The hereditary traits of the offspring are in this 



