EVOLUTION OF THE COLORS OF BIRDS. 117 



Evolution Theory," ^ Mr. Wallace objects most em- 

 phatically to the view that any specific characters are 

 without use. He points to the progress which has been 

 made of late years in discovering the use of structures 

 or characters which were formally thought to be of no 

 utility, and calls particular attention to the colors of the 

 higher vertebrates as illustrating his point. He men- 

 tions the fact that while the colors of wild animals are 

 so generally constant (white or pied varieties being 

 speedily obliterated) domestic breeds exhibit the greatest 

 inconstancy and diversity in this respect; proving, as 

 he thinks, that the colors of all wild animals must be 

 useful, even though we cannot always see how they are 

 so, and that their lack of uniformity under domestica- 

 tion is due to the fact that they are no longer of utility. 

 He then gives illustrations of the various forms of 

 adaptive markings — protective and warning colors and 

 recognition markings. He says: " This need of easy 

 recognition by each species of its own kind and of the 

 sexes by each other, will probably explain at once those 

 slight diversities of colour and marking, which, more 

 commonly than any other characters distinguish closely 

 allied species from each other, and also the constancy 

 and bilateral symmetry of the colouration of wild ani- 

 mals." 



With regard to the swamping effects of free intercross- 

 ing, Mr. Wallace says the difficulty is removed by con- 

 ceding "that the same variation occurs simultaneously 

 in a number of individuals inhabiting the same area." 

 Mr. Romanes had denied this, but Mr. Wallace j^resents 

 an array of facts taken from Mr. J. A. Allen's Winter 

 Birds of Florida, in support of his contention. 



So far as the infertility of species with one another 

 is concerned, Mr. Wallace denies that the facts support 



*Fortuigbtly Eeview, slvi, pp. 300-316. 



