ORGANIC EVOLUTION 



in such a way as to give more perfect conformity to the 

 environmental conditions; while in artificial selection the 

 modification is such as to make the altered form more per- 

 fectly suit the uses to which man wishes to put it. The 

 results of artificial selection are usually more quickly seen ; 

 for the selection for breeding purposes of individuals with 

 the desirable qualities is generally more rigid than in nature, 

 where the more and the less adapted forms will for a time 

 breed side by side, the more perfect gradually predominat- 



ino- more and more. 



O 



The extent of the 

 modification produced by 

 artificial selection is very 

 great in many cases. 

 Notice the common do- 

 mestic chickens, in which 

 the different breeds differ 



FIG. 5. Skull of Polish fowl, showing the pe- 

 culiar knob that has been developed in front of the 

 brain case. From Wright's A T ew Book of Poultry, 

 by the courtesy of Cassell & Company. 



from one another to such 

 a degree that if they 





occurred in nature the several kinds would be referred not 

 only to different species, but to different genera (Plates 12-19 

 and Fig. 5). Compare the slender "game" (Plate 12, A; 

 16, B], which most closely of all resembles the ancestral 

 " jungle fowl " (Plate 16, A\ with the heavy " Brahma " (Plate 

 15, A, B] or "Cochin-china" (Plate 15, C,D\ 19, B\ or with 

 the long-tailed "Japanese" cocks (Plate 17), or with the little 

 "bantam" (Plate 14, D ; 19, C). Or notice the varieties of 

 pigeons, as shown in another illustration (Fig. 6; Plate 20). 

 These races differ from one another anatomically and 

 in disposition as much as do natural species, yet in one 

 important particular they fail to resemble natural species. 



