NATURAL SELECTION 71 



hypothesis accords with, and explains the general 

 phenomena of Nature. On the other hand, the ordinary 

 belief that the amount of possible variation is a strictly 

 limited quantity is likewise a simple assumption." 



Before explaining the evolutionary action of the 

 individual variation that occurs in the course of 

 many successive generations, as it is described by 

 Darwin, I shall make a few remarks upon the last 

 three sentences of the above quotation. When he 

 asserts that individual differences of the same kind 

 perpetually recur, Darwin does not mean to affirm 

 that they occur uninterruptedly in successive genera- 

 tions, as the result of continuous and unbroken heredity 

 from both parents. He simply means that sporadically, 

 here and there, they occur frequently in individuals of 

 a species as the result of the variability of the species. 

 As my argument proceeds, it will be seen how un- 

 warrantable is Darwin's assumption that in such 

 circumstances individual differences should be per- 

 petuated, or preserved beyond a few generations. 



Again, let us consider what cogency we should attach 

 to the statement that we are to judge of the truth of 

 his hypothesis by seeing how far it accords with, and 

 explains the general phenomena of Nature. The 

 principle of evolution, per se, is one thing. A hypo- 

 thetical theory of the manner in which the principle 

 works is quite another thing. The hypothesis may be 

 capable of being disproved, as, for instance, being shown 

 to contravene inviolable laws of Nature ; and yet, so 

 long as it is allowed to go unchallenged, it may stand 



