The Making of Species 



continuous and discontinuous variations. The 

 former are slight departures from the normal ; 

 the latter are considerable deviations from the 

 mean or mode ; great jumps, as it were, taken by 

 nature, as, for example, the pea and the rose 

 combs of fowls, which were derived from the 

 normal single comb. 



" At long intervals of time," wrote Darwin, 

 "out of millions of individuals reared in the 

 same country and fed on nearly the same food, 

 deviations of structure so strongly pronounced as 

 to deserve to be called monstrosities arise, but 

 monstrosities cannot be separated by any distinct 

 line from slighter variations." Therefore it is 

 evident that he regarded the difference between 

 continuous and discontinuous variations as not 

 one of kind, but merely of degree. To the 

 discontinuous variations Darwin attached very 

 little importance from an evolutionary point of 

 view. He looked upon them as something 

 abnormal. 



" It may be doubted," he wrote, " whether 

 such sudden and considerable deviations of 

 structure such as we occasionally see in our 

 domestic productions, more especially with plants, 

 are ever permanently propagated in a state of 

 nature. Almost every part of every organic 

 being is so beautifully related to its complex 

 conditions of life that it seems as improbable 

 that any part should have been suddenly pro- 



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