EVOLUTION OF THE COLORS OF BIRDS. 105 



of the genus Homo, even though every individual had a 

 nasal twang which unerringly indicated the section from 

 which he came? The Code of Nomenclature of the 

 American Ornithologists Union^ contains the following 

 apt sentences on this subject: ^' There is no inherent 

 zoological difference between a ' generic ' and a ' specific ' 

 name, — the nomen genericum and the nomen triviale of 

 earlier zoologists. Both alike designate a 'group' in 

 Zoology, — the one a group of greater, the other a group of 

 lesser classificatory value. Some necessary distinction, 

 which has been misconceived to exist between these two 

 names, is simply a fortuitous matter of the technique of 

 nomenclature, apparently arising from the circumstance 

 that the generic and the specific names form the con- 

 trasted though connected terms of a binomial designa- 

 tion. Recognition of the scientific fact, that a 'species,' 

 so called, is not a fixed and special creation, as long 

 supposed, but simply a group of the same intrinsic 

 character as that called a ' genus,' though usually less 

 extensive, and always of a lower taxonomic rank, has 

 done more than any other single thing to advance the 

 science of Zoology; for the whole theory of evolution 

 turns, as it were, upon this point." 



From the above it is apparent that the decision of 

 whether any particular group of individuals constitutes 

 a species or some greater or lesser taxonomic division, 

 must be more or less arbitrarily settled. In general, 

 however, it may be said that a species in science is a 

 group of individuals morphologically isolated from every 

 other group by at least one peculiar character.! 

 Wherever a group is not completely isolated, but con- 

 nected by living intervening forms with some other 



* pp. 26-27. 



t The word morphological is here used in its broadest interpretation, as 

 distinguished from i^hysiological, and of course includes color changes. 



