No. 602J THE SELECTION PROBLEM 



81 



shows that the principle of the gradual accumulation by 

 continued selection of minute somatic variations has had 

 no essential part in the origin or amelioration of cer- 

 tainly a great many of the best varieties of agricultural 

 plants which we have to-day. The essential factors which 

 have been involved in the production of our best fruits, 

 grains, vegetables, flowers, etc., have been (1) the im- 

 proved conditions of domestication, (2) mutations, lead- 

 ing at once to new and better forms, (3) hybridization, 

 wliich by new combinations of characters and as a result 

 of heterosis^^ j^^s led to amelioration, and (4) the puri- 

 fication of previously mixed races or varieties by selective 

 sorting. It is to the overwhelming importance of one or 

 a combination of these factors that the "experience of 

 breeders" points and not to Darwinian selection. 



But what of the animal side? Here the true facts are 

 much more difficult to get at; in part for reasons which 

 have been developed earlier in this paper, and in part for 

 the reason that the making of new breeds of domestic 

 animals is no longer going on to any extent except in the 

 smaller sorts such as poultry. As has been pointed out 

 elsewhere,^* this is primarily a result of the great devel- 

 opment of the system of pedigree registration, which 

 puts a ban on cross breeding in cattle, horses, etc. 



So then let us take as our first example one from poul- 

 try breeding where unequivocal facts are available. In 

 his "Organic Evolution" Metcalf^^ makes the following 

 statement : 



The extent of the modification produced by artificial selection is very 

 great in many cases. Notice the common domestic chickens, in which 

 the different breeds differ 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. Compare the slender " game " 

 which most closely of all resembles the ancestral "jungle fowl," with 

 the heavy " Brahma " or " Cochin-china," or with the long-tailed " Jap- 

 anese " cocks, or with the little " bantam." 



33 East, E. M., and Hayes, II. K., U. S. Dept. Agr., Bur. Plant Industry, 

 Bulletin 243, 1912. 



3* Pearl, R., "Modes of RcPearoh in Genetics." New York, 1915. 



35Metcalf, M. M., "Organic Evolution." New York, 1904. 



