Heredity and Natural Selection. 281 



facts, that the logical conclusion seems to be, not that 

 natural selection is at fault, but that Darwin's opinion, 

 that variations are fortuitous, is an error. 



According to our view of the cause of variation, it is 

 plain that a change in the environment, affecting many 

 individuals of a species in the same way, will cause, in 

 succeeding generations, variation of the same cells in all 

 or nearly all of them. It is also clear that since a change 

 in one cell of an orsianism will disturb the harmonious 

 adjustment of all adjacent or related cells, any variation 

 "which makes its appearance will become more marked 

 instead of being obliterated, in the offspring of succes- 

 sive generations. 



I think it is clear, without further discussion, that 

 our theory of heredity entirely does away with this very 

 serious difficulty, and furnishes a firmer basis for the 

 theory of natural selection. It is also clear that this 

 cannot be said of the Pangenesis hypothesis, or of any 

 other hypothesis which has been proposed. 



Tlie Formation of Complicated Organs hy the Natural 

 Selection of Fortuitous Variations demands Unlimit- 

 ed Time. 



There is another objection of nearly the same char- 

 acter, which must have struck every thinker with more 

 or less force. How are the various organs of a highly 

 complicated organism, or the various structures w^hicli 

 enter into the formation of a complicated organ, kept in 

 harmonious adjustment to each other by the selection of 

 variations which are, in Darwin's sense, fortuitous? It 

 is plain that, as soon as one part has varied in any direc- 

 tion, the harmonious adjustment of related parts w^ill be 

 disturbed, and that tliey too must vary correspondingly 

 in order to restore the proper tone to the whole, and it 

 is equally clear that even a slight change in a compli- 



