No. 562] 



THE PROBLEM OF INBREEDING 



587 



In the limiting case of the closest inbreeding possible 

 the successive Z 's will have the values given in the fol- 

 lowing table. 



TABLE I 



Case of the Most Ixtknsk Inukkkimnc. Possible (Brother X 



From this table it is apparent that while the narrowing 

 or exclusion of the possible different source lines of 

 descent proceeds very rapidly in the first few generations 

 of brother X sister breeding, only relatively little change 

 is made by further generations of this sort of breeding. 

 Thus in seven generations of brother X sister breeding 

 all but about 1.5 per cent, of the potentially different an- 

 cestral "blood-lines" will have been eliminated. After 

 16 generations of this sort of breeding (a number easily 

 attainable in ordinary breeding experiments) an indi- 

 vidual so bred can by no chance possess more than 3/1000 

 of one per cent, of the different lines of ancestral descent 

 which are theoretically possible. This table strongly sug- 

 gests that if, in an experiment to test the influence of in- 

 breeding, no particular effect is observed during ten gene- 



