THE 



AMERICAN NATURALIST 



Vol. XLVII October, 1913 No. 562 



A CONTRIBUTION TOWARDS AN ANALYSIS OF 

 THE PROBLEM OF INBREEDING 1 



DR. RAYMOND PEARL 



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 destruc- 

 tive 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 ten- 

 dency 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 evidence. Aside from a relatively 

 small amount of definite experimental data one's judg- 

 ment in the matter (so far as it is not wholly speculative) 

 is finally formed on the basis of his interpretation of the 

 vast accumulation of material comprised in the recorded 

 experience of the breeders of registered (pedigreed) 

 livestock. 



This material recorded in the books of registration far 

 exceeds in amount and in diversity any which could pos- 

 sibly be obtained experimentally on the same forms of 

 life. It must be said, however, that the discussion of it 



1 Papers from the Biological Laboratory of the Maine Agricultural 

 Experiment Station, No. 47. 



577 



