EVOLUTION OF THE COLORS OF BIRDS. 53 



that variations occurred in past geological ages different 

 in nature from those which occur to-day? If we do not 

 do so, from which class of the variations above enumer- 

 ated were feathers evolved, or horns, for example? 

 Singularly enough, Wallace, an avowed opponent of 

 Lamarckianism, triumphantly appeals to the principles 

 of use in the one difficult variation which he does really 

 explain, the shifting of the eye of the flatfish.* If in- 

 dividual variation does not normally originate new parts, 

 such as horns, for example, and I know of no reason 

 either theoretical or practical for assuming that it does, 

 then there must be some other factor occasionally called 

 into play; but if some factor exists which must be opera- 

 tive at rare intervals it is but reasonable to assume that 

 it is constantly operative to some extent rather than to 

 suppose that it is lying idle until natural selection is 

 obliged to call upon it to lend a helping hand. 



The above considerations lead to another frequently 

 urged difficulty that even supposing the necessary varia- 

 tions did occur, we are obliged to assume that they were 

 advantageous. That incipient modifications of an organ- 

 ism are always advantageous is considerable of an assump- 

 tion. It seems incredible, indeed, that some very pro- 

 nounced distinctions can be of utility. Thus it seems 

 difficult to explain, by utility or adaptation, the fact that 

 in California a species of magpie is found identical with 

 the one found east of the Sierra Nevada Mountains, with 

 the exception of being smaller and having the bill bright 

 yellow instead of black. The birds are well isolated geo- 

 graphically throughout the greater part or the whole of 

 their range, so the difference could hardly be accounted 

 for by the theory of recognition markings. This is but 

 one of a great number of instances of a similar nature 



* 1. c., pp. 129-130. 



