108 CONCLUDING EEMARKS. Chap. XXVllI. 



of fowls, by attending to tiie form of the comb, or to the 

 plume of feathers on the head. By attending to the external 

 form of the pouter-pigeon, he has enormously increased the 

 size of the oesophagus, and has added to the number of the 

 ribs, and given them greater breadth. With the carrier- 

 pigeon, by increasing through steady selection the wattles 

 on the upper mandible, he has greatly modified the form of 

 the lower mandible ; and so in man}^ other cases. Natural 

 species, on the other hand, have been modified exclusively 

 for their own good, to fit them for infinitely diversified con- 

 ditions of life, to avoid enemies of all kinds, and to struggle 

 against a host of competitors. Hence, under such complex 

 conditions, it would often happen that modifications of the 

 most varied kinds, in important as well as in unimportant 

 parts, would be advantageous or even necessary ; and they 

 would slowly but surely be acquired through the survival 

 of the fittest. Still more important is the fact that various 

 indirect modifications would likewise arise through the law 

 of correlated variation. 



Domestic breeds often have an abnormal or semi-monstrous 

 character, as amongst dogs, the Italian greyhound, bulldog, 

 Blenheim spaniel, and bloodhound, — some breeds of cattle 

 and pigs, — several breeds of the fowl, — and the chief breeds 

 of the pigeon. In such abnormal breeds, parts which differ 

 but slightly or not at all in the allied natural species, have 

 been greatly modified. This may be accounted for by man's 

 often selecting, especially at first, conspicuous and semi- 

 monstrous deviations of structure. We should, however, 

 be cautious in deciding what deviations oiight to be called 

 monstrous : there can hardly be a doubt that, if the brush 

 of horse-like hair on the breast of the turkey-cock had first 

 appeared in the domesticated bird, it would have been con- 

 sidered as a monstrosity ; the great plume of feathers on the 

 head of the Polish cock has been thus designated, though 

 plumes are common on the heads of many kinds of birds ; 

 w-e might call the wattle or corrugated skin round the base 

 of the beak of the English carrier-pigeon a monstrosity, 

 but we do not thus speak of the globular fleshy excrescence 

 at the base of the beak of the Carpopliaga oceanica. 



Some authors have drawn a wide distinction between 



