Recurrent Mutations 



pure ancestors and breed true inter se. Nor is 

 this all. 



Experience shows that where a mutation, or 

 sport, or discontinuous variation occurs, it fre- 

 quently repeats itself ; for example, the black- 

 winged sport of the peafowl has occurred several 

 times over and in different flocks of birds. The 

 sport or mutation must have a definite cause. 

 There must be something within the organism, 

 something in the generative cells, which causes 

 the mutation to arise ; and hence, on a priori 

 grounds, we should expect the same mutation to 

 arise about the same time in many individuals. 

 It seems legitimate to infer that things have 

 been quietly working up to a climax. When 

 this is reached there results a mutation. There- 

 fore we should expect sudden mutations to appear 

 simultaneously in a number of individuals. To 

 this important subject we shall return. 



8. An almost insuperable objection to the 

 theory that species have originated by the action 

 of natural selection on minute variations, is that 

 such small differences cannot be of a life-or-death 

 value, or, as it is usually called, a survival value 

 to their possessor. But if evolution is the result 

 of the preservation by natural selection of such 

 slight variations, it is absolutely necessary that 

 each of these should possess a survival value. 



As D. Dewar has pointed out, on page 704 of 

 vol. ii. of The Albany Review, it is only when the 



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