500 GENETICS IN RELATION TO AGRICULTURE 



tion which has been made use of in the establishment of modern breeds 

 of domestic animals has come from amphimixis, the result of polyphyletic 

 origin. But modern breeds have become highly standardized and they 

 are closely guarded by rigid rules of pedigree registration. In conse- 

 quence improvement within them has been effected purely by methods 

 of selection without hybridization between breeds. In poultry, however, 

 and here again we turn to Pearl for data, new breeds are still being 

 created, and almost entirely by methods of hybridization. Thus for 

 practically every variety of larger domestic fowl there is a corresponding 

 bantam variety. Pearl sent queries to bantam breeders in all parts of the 

 world for the purpose of obtaining information upon the method of 

 creating new varieties of bantams. Here it would seem was an ideal test 

 for the utility of Darwinian selection in the establishment of breeds, for 

 it would appear to be a very direct mode of attack in breeding bantams 

 corresponding to a given larger variety of fowl simply to select for smaller 

 size within the larger breed. Pearl's enquiries brought out the fact, 

 however, that in no case were bantam breeds created in this fashion, but 

 always by crossing the larger breed with some bantam variety and then 

 selecting within the hybrid progeny of subsequent generations. In view 

 of the demonstration of the relatively simple Mendelian heredity of body 

 weight in Seabright X Hamburg crosses which has been demonstrated 

 by Punnett and Bailey, we can readily understand how this method 

 should be quickly and uniformly successful. The creation of bantam 

 varieties of fowls, therefore, strikingly bears out this general thesis, that 

 so far as the results of selection go in actual practice, the isolation 

 interpretation is sufficient to account for all facts. The creative view 

 of selection is an uncertain doctrine to accept for guidance. 



Selection and Breeding Methods. Finally it becomes necessary to 

 again point out that a change in interpretation does not necessarily call 

 for a change in breeding methods. In fact it can be shown that in general 

 those breeding methods have been most successful which are most closely 

 in accord with the isolation view of heredity. This fact is particularly 

 patent when the earlier histories of breeds is taken into account, and the 

 vast amount of inbreeding which has been employed by the best of these 

 old pioneer breeders is given a true valuation. For inbreeding determines 

 the fixing of a given genotypic constitution, because in such a system of 

 breeding family excellence is the basis of judgment, just as in the suc- 

 cessful selection for high winter egg production progeny test was the 

 basis of selection for breeding stock. That most famous of all early 

 breeders, Robert Bakewell, when he set about establishing his herds 

 made excursions all over Britain for the purpose of selecting and purchas- 

 ing the best of all sorts for his foundation stock. However, after he had 

 brought this stock together he used only the progeny of these animals in 



