574 



THE AMEBIC AN NATURALIST 



[Vol. XLIX 



From this table it appears that the values of the coefficients of 

 inbreeding- will be exactly the same for this type of mating as iti 

 the case of single cousin mating. Or, in other words, Z's form 

 the following series. 



TABLE II 



From the data presented in this and former papers it is clear 

 that inbreeding continued for about ten generations, quite re- 

 gardless of the type of mating, provided only it be continuously 

 followed, leads to within one or two per cent, of complete "con- 

 centration of blood. ' ' The bearing of this result upon the general 

 question of the degree of inbreeding which exists in the ancestry 

 of our domestic animals to-day is obvious. To consider but a 

 single case : In 1789 3 a law was passed prohibiting the importa- 

 tion of cattle into the Island of Jersey. Hence it follows that all 

 pure-bred Jersey cattle of the present time must be of 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 generations 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. This 

 is not the place to go in detail into the discussion of inbreeding in 

 Jerseys, especially as I hope shortly to publish the results of an 

 extensive study of this matter, but it seems desirable to emphasize 

 the bearing of such hypothetical pedigrees for particular types 

 of mating as are given in this and earlier papers, on the general 

 problem of inbreeding. 



It is possible to extend now somewhat the table of general 

 equations given by Jennings* for coefficients of inbreeding after 



s Teste Eees's Encyclopedia and H. S. Kedfield, Natl. StocTcman and 

 Farmer, December 15, 1892. 



* Amer. Nat., Vol. XLIII, p. 695, 1914. 



