Psychophysical Parallelism in Evolution 17 



so far as there are known facts in the particular case which 

 lend themselves to such procedure. 



The philosophical problem is illustrated by a similar dia- 

 gram in the section below already referred to (Chap. IX. 

 § 3). In that connection it is a question of reaching an inter- 

 pretation in a statement in which the independence of the 

 two series is in so far denied — the representation being that 

 of a possible single line which can be substituted for the two 

 in their development. A similar philosophical problem is 

 open also in the matter of evolution. Such an interpreta- 

 tion in either province, it is maintained in the later place, is 

 not possible to the scientific inquirer as such, although it 

 may be possible to arrive at a philosophical explanation of 

 the dualism of mind and body. In our present connection 

 the urgent need is in another direction — to hold a level 

 balance and give each side its due. It is an equally 

 embarassing thing for the scientific inquirer in one case to 

 be a monist to such a degree as to deny one of these lines 

 altogether — the mental in favour of the physical * short- 

 hand, ' or the physical in favour of the mental — and in 

 another case to insist upon the separateness of what nature 

 shows us always joined together, to the extent of refusing 

 to use facts from one of the series to illumine and even 

 to explain facts in the other. 



This last-mentioned attitude is especially to be con- 

 demned in the discussion of genetic questions — those of 

 development and evolution. Here the question turns upon 

 the genetic antecedents of a given fact, be it function, 

 act of behaviour, mental state, instinct, or other, in this 

 organism or that. No tracing of genesis is possible, of 

 course, except by actual observation of the facts under 

 which the phenomenon in question arises. Now to refuse 

 c 



