TOPICS IN INHERITANCE. 99 



known. If, unconsciously or not, a unit character arising as a sport has 

 been preserved under domestication, it will persist even though the race 

 bearing it become feral. 



Positive support for the mutation theory is gained from a consideration of 

 the characteristics of poultry. ^'Our study has shown them to be, for the 

 most part, of the order of integral uaii^chjj,racters. As such they could 

 hardly have been "gradually built up." Being indivisible they must have 

 appeared at once, roughly in their present form. The very existence of unit 

 characters is proof of the mutation theory. 



That many characteristics of organisms have not been built up, but have 

 suddenly appeared complete, may be inferred from peculiarities of the char- 

 acters other than their integral nature. For, first, not all kinds of charac- 

 teristics have been evolved in domestic poultry, but for the most part only 

 such as occur elsewhere among wild races. Thus, for example, booted feet, 

 as found in the grouse ; crest on head, as seen in the umbrella bird (Ccf>halop- 

 terus), and long tail, as seen also in the widow bird (Chera). Secondly, 

 many of the characteristics of domestic poultry are of the order of mutations 

 in so far as they are almost pathological, e. g., taillessness, rose comb, silky 

 and frizzled feathers, cerebral hernia, polydactyl feet, albinism. These char- 

 acters, cropping out in the sporting organism and not being prejudicial to 

 its well-being, have been preserved by the fancier ; they doubtless arose sud- 

 denly, as we find arising suddenly to-day other characters, which we discard 

 because incompatible with a healthy stock such as featherlessness, cross-bill, 

 and. imperfect development of toes. If these characteristics appeared sud- 

 denly and not by being "built up," as we know is the case, then so, doubt- 

 less, have others. The evidence that many, if not most, characteristics of 

 poultry have arisen suddenly, without having been sought and laboriously 

 built up by man, is convincing, and there can hardly be any escape from the 

 conclusion that here evolution has been largely, though not exclusively, by 

 mutation. 



