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COOK 



or otherwise. The degenerate nature of mutative variations of 

 narrow-bred groups and the fact that they usually fade out en- 

 tirely when brought into contact with the unrestricted descent 

 of the wild type, are further practical reasons for the complete 

 divergence between the mutation theory and that of kinetic pre- 

 potenc}''. But even mutations are usually prepotent among 

 their own equally narrow-bred relatives, and thus afford at least 

 an illustration of the power of genetic variations to maintain 

 themselves and gradually transform broad-bred species in nature. 



Instead of compelling us to abandon the conception of evolu- 

 tion as a process of gradual change in the characters of a spe- 

 cies, mutations and Mendelism in reality strengthen and rein- 

 force this older idea of continuity. They show that progress 

 does not depend upon environmental causes, either direct or in- 

 direct. The studies of mutations have made it certain that 

 diverse variations occur, even under the same condition, and 

 Mendelism demonstrates that such variations can also be pre- 

 served without isolation. Both Mendelism and mutation, in their 

 typical forms, represent abnormal conditions of restricted de- 

 scent, but they may still have great evolutionary interest if we 

 accept them as evidence, or even as suggestions, that less ac- 

 centuated forms of the same phenomena of inheritance are con- 

 cealed among the more nearly indiscriminate diversities shown 

 by the members of wild species in nature. 



Evolution is a process of change in the characters of spe- 

 cies, and not merely the origination of new species, either by 

 mutative leaps or by Mendelian combinations of characters. 

 Evolution is accomplished by the gradual, constructive synthesis 

 of variations. Darwin may have been in error in supposing 

 that evolution is actuated by selective agencies of the environ- 

 ment, or that the steps by which it is accomplished are infini- 

 tesimally gradual, but it has yet to be shown that he was in 

 error regarding the general continuity' of the motion as indicated 

 by the continuity of the differences inside the species and also 

 of the species themselves when viewed as members of genera, 

 or of genera when grouped in families. 



This fact of continuity convinced Darwin of evolution, and 

 not natural selection and other theories by which he attempted 



