THE CLASSIFICATION OF BIRDS 13 



recent origin, in any scheme in which it is attempted to arrange 

 Birds in natural groups. I propose, therefore, to confine my 

 attention to the inquiry, how far it is possible to classify existing 

 birds in a natural manner that is to say, to arrange them in 

 groups which may be diagnosed by the possession of certain 

 characters which have probably been inherited from common 

 ancestors, and which, there is every reason to believe, have not 

 been acquired by some species in the group independently of other 

 species in the same group. This assumption, however, does not 

 exclude the possibility of the same character, or a very similar 

 character, having been independently acquired by species in other 

 groups. 



Much has been published respecting the classification of 

 Birds since Huxley's celebrated paper on the bones of the palate 

 astonished the ornithological world by proving at least that the 

 existing systems of classification had no scientific basis. 



A great deal of scientific work has been done in various de- 

 partments of Ornithology since then, but little or no progress has 

 been made towards a true classification of Birds. Every one admits 

 that the ideal system of classification must be based upon genetic 

 affinity, and it is further admitted by most ornithologists that the 

 only clue to genetic affinity between any two birds is the discovery 

 that they both possess a certain character or characters which 

 they have presumably inherited from common ancestors. 



An ideal classification would, if it could be discovered, arrange 

 birds in groups so constituted that each character could be traced 

 to its origin. Every attempt to discover this ideal classification 

 has hitherto been an absolute failure ; and it can almost be proved 

 that it involves a mathematical impossibility, unless we admit that 

 a primitive character may be independently modified in a special 

 direction by two distantly related families under the influence of 

 similar causes, and also that the influence of other causes may 

 afterwards produce a reversion to the primitive character in some 

 of the descendants. This admission is almost tantamount to a 

 confession that the attempt to arrive at finality in the classifica- 

 tion of Birds is hopeless. 



We seem to be compelled to assume the truth of one or both 

 of the following hypotheses : Identical characters in different 

 species may in some cases have been independently acquired ; 

 or, having been acquired, they may be subsequently lost by one 

 or more groups of descendants. 



