CHAPTER XL 



NATURAL SELECTION BY THE STRUGGLE FOR EXIST- 

 ENCE. DIVISION OF LABOUR AND PROGRESS. 



[uteraction of the Two Organic Formative Causes, Inheritance and Adapta- 

 tion. — Natural and Artificial Selection. — Struggle for Existence, or 

 Competition for the Necessaries of Life. — Disproportion between the 

 Number of Possible or Potential, and the Number of Keal or Actual 

 Individuals. — Complicated Correlations of all Neighbouring Organisms. 

 — Mode of Action in Natural Selection, — Homochromic Selection as the 

 Cause of Sjnnpathetic Colourings. — Sexual Selection as the Cause.of the 

 Secondary Sexual Characters. — Law of Separation or Division of 

 Labour (Polymorphism, Differentiation, Divergence of Characters). — 

 Transition of Varieties into Species. — Idea of Species. — Hybridism. — 

 Law of Progress or Perfectioning (Progressus, Teleosis). 



In order to arrive at a right understanding of Darwinism, 

 it is, above all, necessary that the t^YO organic functions 

 of Inheritance and Adaptation, which we spoke of in 

 our last chapter, should be more closely examined. If we 

 do not, on the one hand, examine the purely mechanical 

 nature of these two physiological activities, and the various 

 action of their different laws, and if, on the other hand, we 

 do not consider how complicated the interaction of these 

 different laws of Inheritance and Adaptation must be, we 

 shall not be able to understand how these two functions, by 

 themselves, have been able to produce all the variety of 



