CHAPTER IV 



CERTAIN LOGICAL AND MATHEMATICAL AS- 

 PECTS OF THE PROBLEM OF INBREEDING 1 



I. The Analysis and Measurement of In- 

 breeding 



The effect of inbreeding on the progeny is a 

 much-discussed problem of theoretical biology 

 and of practical breeding. It has been alternately 

 maintained, on the one hand, that inbreeding is 

 the most pernicious and destructive procedure 

 which could be followed by the breeder, and on the 

 other hand, that without its powerful aid most of 

 what the breeder has accomplished in the past 

 could not have been gained and that it offers the 

 chief hope for further advancement in the future. 

 While there is now, among animal breeders at 

 least, a more widespread tendency than was 

 formerly the case towards the opinion that in- 

 breeding per se is not a surely harmful thing, 

 nevertheless this opinion is by no means univer- 

 sally held, and in any case does not rest upon a 

 definite and well-organized body of evidence. 



1 This paper is based upon a series of "Studies on Inbreeding" 

 which have recently been published, chiefly in the American Naturalist, 

 during 1913, 1914, and 1915. 



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