108 MODES OF RESEARCH IN GENETICS 



Bruce Low, though somewhat differently stated, 

 comes to essentially the same thing, so far as I 

 am able to determine from abstracts, this author's 

 original writings not having been accessible to me. 



All systems based on the number of "free 

 generations" alone do not furnish a precise or 

 reliable measure of the real intensity of inbreeding. 

 The essential reason for this failure, stated baldly, 

 is that they do not take account of the composition 

 of the generation to which the "common ances- 

 tors " of an inbred pair belong. 



In developing a general measure of the intensity 

 of inbreeding we may well start from the con- 

 ception set forth in the preceding section ; namely, 

 that the inbred individual possesses fewer different 

 ancestors than the maximum possible number. 

 Besides this factor account must be taken of the 

 generation or generations in which the reduced 

 number of different ancestors is found, and the 

 extent to which these generations are removed 

 (in the sense of Lehndorff discussed above) from 

 the individual or generation under consideration. 

 In other words, the two factors which must be 

 included in a general measure of the intensity of 

 inbreeding are (a) the amount of ancestral reduc- 

 tion in successively earlier generations, and (6) the 

 rate of this reduction over any specified number of 

 generations. 



Both of these demands are met, I think, by 

 taking as a measure of the intensity of inbreeding 



