92 THE THEORIES OF EVOLUTION 



De Vries goes a step farther and thinks that what- 

 ever of slight individual variations is created by se- 

 lection, whether the selection is natural or artificial, is 

 doomed to immutability; consequently, constant nat- 

 ural varieties cannot be produced by the same factors 

 as cultivated varieties, which are due to selection di- 

 rected by man. De Vries based upon this difference 

 a new theory of species which will form the subject 

 matter of Chapter XX. 



What general conclusion can we draw from this 

 lengthy expose of the objections raised against 

 the Darwinian or rather the Neo-Darwinian theory? 

 We have not mentioned all of them, we have merely 

 selected the ones which seemed to carry most weight 

 and which have not yet been answered. For instance, 

 a criticism frequently made against the theory of 

 natural selection is that it does not reveal the origin 

 of the different variations but takes them for granted, 

 while their origin is precisely the most puzzling prob- 

 lem. To this we can answer that no theory is ex- 

 pected to solve any problems but those which it raises, 

 and that it has a right to select its own problems. 

 Darwin considers the variations after their appear- 

 ance and believes them to be accidental. It is only 

 there that his explanations begin and it is only within 

 the limits he assigned himself that we may criticise 

 him. 



Other objections are based upon the period of time 



