646 Studies in the Theory of Descent. 



those philosophers who have approached this 

 question with a manv-sided scientific preparation. 

 It can nevertheless be perceived in his case how 

 difficult, and indeed how impossible, it is to esti- 

 mate the trut- value of the facts furnished bv the 



* 



investigation of nature, when we attempt to take 

 up only the results themselves, without being 

 practised in the methods by which these are 

 reached, i. e. without being completely at home 

 in one of the scientific subjects concerned through 

 one's own investigations. It appears to me that 

 the denial of the purely mechanical value of the 

 Darwinian factors of transformation arises in most 

 part from an erroneous classification of the scien- 

 tific facts with which we have to deal. There can 

 certainly be no mistake that the entire philo- 

 sophical conception of the universe, as laid down 

 by Von Hartmann in his " Philosophy of the Un- 

 conscious," is unfavourable to an unprejudiced esti- 

 mate of scientific facts and to their mechanical 

 valuation. 



Variability, heredity, and above all correlation, 

 would not be regarded by Von Hartmann as purely 

 mechanical principles, but he would therein assume 

 a metaphysical directive principle. 



In the first place, as regards variability, Von 

 Hartmann endeavours to show that it is only a 

 quite unlimited variability which suffices for the 

 explanation of necessary and useful adaptations 

 by means of selection and the struggle for ex- 



