Essays on Life 



chance cannot be supposed as likely to be 

 accumulated, for chance is notoriously incon- 

 stant, and would not purvey the variations in 

 sufficiently unbroken succession, or in a suffi- 

 cient number of individuals, modified similarly 

 in all the necessary correlations at the same 

 time and place to admit of their being accu- 

 mulated. It is vital therefore to the theory 

 of evolution, as was early pointed out by the 

 late Professor Fleeming Jenkin and by Mr. 

 Herbert Spencer, that variations should be 

 supposed to have a definite and persistent 

 principle underlying them, which shall tend 

 to engender similar and simultaneous modifi- 

 cation, however small, in the vast majority of 

 individuals composing any species. The exist- 

 ence of such a principle and its permanence is 

 the only thing that can be supposed capable 

 of acting as rudder and compass to the accu- 

 mulation of variations, and of making it hold 

 steadily on one course for each species, till 

 eventually many havens, far remote from one 

 another, are safely reached. 



It is obvious that the having fatally im- 

 paired the theory of his predecessors could 



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