THE PROBLEM OF INBREEDING 127 



exists in the ancestry of our domestic animals 

 to-day is obvious. To consider but a single 

 case : In 1789 1 a law was passed prohibiting the 

 importation of cattle into the island of Jersey. 

 Hence it follows that all pure-bred Jersey cattle 

 of the present time must be the descendants of 

 the relatively few animals on the island in 1790. 

 Taking three years as about the average generation 

 interval in cattle, this means about forty genera- 

 tions since the island was closed to importation. 

 The concentration of lines of descent which must 

 have occurred in this time merely by the dropping 

 of lines and quite regardless of the type of mating 

 is obvious. 



ILLUSTKATION V. THE PEDIGREE OF THE JERSEY 

 COW, BESS WEAVER (155121) 



Leaving now the hypothetical cases, we may 

 consider some pedigrees of actually existing 

 animals. For a first illustration of this sort the 

 Jersey cow, Bess Weaver, may be taken. Her 

 pedigree through four ancestral generations is 

 shown in Pedigree Table VI. 



In the twelfth ancestral generation the theo- 

 retically possible number of different ancestors is 

 4096. In a relatively long pedigree, such as 

 arises in dealing with registered cattle, it would 

 obviously be an extremely tedious business to 



1 Teate Rees's Encyclopedia and H. S. Redfield, Notl. Stockman 

 and Farmer, December 15, 1892. 



