156 MODES OF RESEARCH IN GENETICS 



individual from one not inbred is that the former 

 has fewer different ancestors than the latter. It 

 is believed that the proposed coefficients of inbreed- 

 ing 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 practical fields of stock breeding and eugenics. 



In the second place, attention is called to the 

 fact that inbreeding of considerable degree may be 

 brought about in the entire absence of any kinship 

 between the two individuals bred together, and there 

 is described a method of separately measuring what 

 proportion of the observed inbreeding in a par- 

 ticular case is due to kinship of the parents, and 

 what to earlier ancestral reduplication. A pro- 

 posed coefficient of relationship is described, and 

 its application illustrated by concrete cases. 



In a final section it is shown that logically the 

 general problem of inbreeding must be considered 

 as composed of three distinct elements, viz. : 



1. Inbreeding itself — a system of mating with 

 definite mathematical characteristics. 



2. The genetic consequences of inbreeding. 



3. The physiological consequences of inbreed- 

 ing. A discussion of the second of these elements, 

 the first two sections of the paper having been 

 devoted to a consideration of the first, reviewed 

 the meager work so far done on the theoretical 

 side of the problem. No attempt is made here to 

 discuss in any way the third element of the problem. 



