8o The Origin of Modifications. 



of external conditions, of habit, and of correla 

 tion, Darwin found these factors incompetent to 

 produce the variations presupposed for natural 

 selection in his theory of the origin of species. 

 Accordingly, while they retain their place in the 

 later editions of his work, they are there over 

 shadowed by a more potent cause of modification, 

 which is nothing less than a force inherent in the 



O 



organism itself u an innate tendency to new va 

 riations &quot; or a &quot; spontaneous variability,&quot; as it is 

 indifferently called. The environment is, I have 

 said, still recognized as one of the factors of 

 change ; but since it is shown that similar varie 

 ties are produced from the same species in differ 

 ent environments, and dissimilar varieties in the 

 same environment, it is established that the nat 

 ure of the organism is a much more important 

 factor than the nature of the external conditions 

 of life. &quot;&quot;We clearly see,&quot; says Darwin, &quot; that 

 the nature of the conditions is of subordinate im 

 portance, in comparison with the nature of the 

 organism, in determining each particular form of 

 variation ; perhaps of not more importance than 

 the nature of the spark, by which a mass of 

 combustible matter is ignited, has in determining 

 the nature of the flames.&quot; And if he objects to 

 Ivageli s or Mivart s formulation of an innate 



