MAIXl-: ACRICULTURAL EXPERIMENT STATION. I913. 2^ 



The distinction here is ohviously verbal and not biological. 

 The essential and important biological point is that what is 

 actually done is to purify the stock in respect to all characters 

 tc as great a degree as possible. What the successful breeder 

 aims to do is to get his stock into such condition that he has 

 only one kind of "blood" in it. Expressed more precisely, 

 though unfortunately more technically, it may be said that the 

 breeder endeavors to get his stock homozygous with reference 

 to all important characters or qualities. The quickest way, in- 

 deed the only way, practically to obtain this result is by the 

 practice of some degree of inbreeding. Sometimes a great 

 stride towards the desired end may be made by mating brother 

 and sister or parent and offspring together. 



That a mating of such close relatives will surely result in 

 disaster is one of the carefully nursed superstitions of breeding, 

 which has often been exploded, but will doubtless always be 

 with us. It may be said that all the evidence which may be 

 gleaned from the experience of stock breeders indicates that the 

 results which follow inbreeding depend entirely upon the nature 

 of the individuals inbred. If one inbreeds weak animals, lack- 

 ing in constitutional vigor, and carrying the determinants of 

 undesirable qualities in their germ cells, the offspring resulting 

 from such a mating will undoubtedly be more nearly worthless 

 than were their parents. If, on the other hand, one inbreeds in 

 the same way strong and vigorous animals, high in vitality, and 

 carrying the germinal determiners of desirable qualities there 

 may be expected a corresponding intensification of these quali- 

 ties in the offspring. The time has come when a vigorous pro- 

 test should be made against the indiscriminating condemnation 

 of inbreeding. It should be clearly recognized that if the ex- 

 perience of stock breeders extending throughout the world, 

 and as far back as trustworthy data are available, means any- 

 thing at all it plainly indicates that some degree of inbreeding* 

 is an essential to the attainment of the highest degree of suc- 

 cess in the breeding of animals. 



This contention receives full support from the results of 

 modern exact studies in genetics. Such studies show that tlie 



* Of course if the term "inbreeding" makes too violent a strain upon 

 anyone's prejudices, there is no objection to his using for the practice 

 the term "line-breeding," or some other even milder designation. 



