Characters as Adaptive and Specific. 181 



dispute the consequence is tantamount to denying the 

 theory from which it is derived. In short, as before 

 stated, it is a question of theory, not a question of 

 fact : our difference of opinion is logical, not biological : 

 it depends on our interpretation of principles, not 

 on our observation of species. It will therefore be 

 my endeavour to show that the reasoning in question 

 is fallacious : that it is not a necessary deduction 

 from the theory of natural selection that no character- 

 istic form or marking, no peculiarities of instinct or 

 of habit, can exist, but which must now be, or once 

 have been, useful, or correlated with some other 

 peculiarity that is useful. 



' The tuft of hair on the breast of a wild turkey- 

 cock cannot be of any use, and it is doubtful whether 

 it can be ornamental in the eyes of the female bird ; 

 indeed, had the tuft appeared under domestication, 

 it would have been called a monstrosity 1 /' 



As a matter of common sense, unprejudiced by 

 dogma, this appears to be a perfectly sound judgement; 

 but if Wallace had asked Darwin to prove such 

 a negative, Darwin could only have replied that it 

 was for Wallace to prove the affirmative and thus 

 the issue would have been thrown back upon a dis- 

 cussion of general principles. Then Wallace would 

 have said " The assertion of inutility in the case of 

 my organ or peculiarity which is not a rudiment or 

 a correlation is not, and can never be, the statement 

 of a fact, but merely an expression of our ignorance of 

 its purpose or origin 2 ." Darwin, however, would have 

 replied : " Our ignorance of the laws of variation is 



1 Origin of Species, p. 70 : italics mine. 

 * Darwinism, p. 137 : italics mine. 



