6 Introductory Remarks 



tion of new species by the cumulative effect of aimless 

 fluctuating variations is not tenable because fluctuating 

 variation is not hereditary ; but this would only demand 

 a slight change in the theory; namely a replacement of 

 the influence of fluctuating variation by that of equally 

 aimless mutations. With this slight modification which 

 is proposed by de Vries, ' Darwin's theory still serves 

 the purpose of explaining how without any pre-estab- 

 lished plan only purposeful and harmonious organisms 

 should have survived. It must be said, however, 

 that any theory of life phenomena must be based on 

 our knowledge of the physicochemical constitution of 

 living matter, and neither Darwin nor Lamarck was 

 concerned with this. Moreover, we cannot consider 

 any theory of evolution as proved unless it permits us 

 to transform at desire one species into another, and 

 this has not yet been accomplished. 



It may be of some interest to point out that we do 

 not need to make any definite assumption concerning 

 the mechanism of evolution and that we may yet be 

 able to account for the fact that the surviving organ- 

 isms are to all appearances harmonious. The writer 

 pointed out that of all the 100,000,000 conceivable 

 crosses of teleost fish (many of which are possible) 

 not many more than 10,000, i. e., about one-hundredth 

 of one per cent., are able to live and propagate. Those 

 that live and develop are free from the grosser type 



* de Vries, H., Die Mutationstheorie. Leipzig, 1901. 



