614 



THE AMERICAN NATURALIST [Vol. XLVII 



than the latter. It is believed that the proposed coeffi- 

 cients of inbreeding' may be made extremely useful in 

 studies of the problem of the effect of inbreeding, whether 

 in relation to its purely theoretical aspects, or in the prac- 

 tical fields of stock-breeding and eugenics. In discussing 

 the relation of the proposed coefficients of inbreeding to 

 the zygotic constitution of individuals it is shown that the 

 common assumption, that (a) self-fertilization, and (b) 

 the closest inbreeding possible with obligate bisexual 

 organisms (brother X sister breeding), are equivalent 

 processes, is not well founded in fact. The automatic 

 increase of the proportion of homozygotes which neces- 

 sarily follows continued self-fertilization does not neces- 

 sarily follow inbreeding of any other sort. Inbreeding 

 of any other type than self-fertilization, unless accom- 

 panied by selection, does not change the proportion of 

 homozygotes and heterozygotes (with reference to any 

 possible genetic differences) in the progeny populations. 

 Inbreeding reduces the number of different hereditary 

 factors in the stock. 



