BULLETIN No. 215. 



THE MEASUREMENT OF THE INTENSITY OF 

 INBREEDING/ 



Raymond Peari,. 



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 inbreed- 

 ing is the most pernicious and destructive procedure Which 

 could be followed by the breeder, and on the other hand, that 

 v/ithout its powerful aid most of what the breeder has accom- 

 plished 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 

 inbreeding per se is not a surely harmful thing, nevertheless 

 this opinion is by no means universally held and in any case 

 does not rest upon a definite and well-organized body of evi- 

 dence. Aside from a relatively small amount of definite experi- 

 mental data one's judgment in the matter (so far as it is not 

 wholly speculative) is finally formed on the basis of his inter- 

 pretation of the vast accumulation of material comprised in the 

 recorded experience of the breeders of registered (pedigreed) 

 livestock. 



iThis bulletin is essentially an abstract (with some new material — see 

 p. 134) of a more extended technical discussion of the subject published, 

 with the title "A Contribution towards an Analysis of the Problem oi 

 Inbreeding," in the American Naturalist (Vol. XLVII, 1913). The 

 complete paper contains illustrative pedigrees and examples of the cal- 

 culation of coefficients of inbreeding, together with a more detailed dis- 

 cussion of the theoretical significance of these coefficients. Anyone 

 wishing to make use of these coefficients of inbreeding should consult 

 the original paper, in addition to this abstract. The paper referred to 

 is not available for general distribution by the Maine Agricultural Ex- 

 periment Station. Recourse must be had by those wishing to examine 

 it to the files of the American Naturalist, a journal available in many 

 of the larger public libraries, or by purchase at a nominal cost from the 

 publishers. 



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