78 SPECIES NOT 



CHAPTER V. 



The intercrossing of individuals is the next 

 subject treated of by Mr. Darwin ; and it gives 

 him an opportunity of enunciating a most ex- 

 traordinary and uncomfortable doctrine, namely, 

 that he believes "that it is a general law of 

 nature, (utterly ignorant though he be of the 

 meaning of the law,) that no organic being 

 self-fertilizes itself for an eternity of generations; 

 but that a cross with another individual is 

 occasionally (perhaps at very long intervals) 

 indispensible." 



As this theory is supported in the present 

 volume by the weakest possible evidence, and as 

 Mr. Darwin confesses there are difficulties which 

 he is still endeavouring to solve, I will pass it 

 over with the simple expression, that I believe 

 it to be among the most improbable speculations 

 contained in the book. The circumstances 

 favourable to natural selection Mr. Darwin con- 

 siders are, 1. Large amount of inheritable 

 and diversified variability. 2. Large number of 

 individuals. 3. Large areas*of action. 4.- 

 I ntercrossing. 5 . Isolation. 



Extinction Mr. Darwin considers to be inti- 

 mately connected with "natural selection ;" because, 

 as this latter has to benefit the being, the less 



