METHODS OF BREEDING 581 



educated people. The old Mosaic laws forbade the marriage of closely 

 related individuals, and complex systems of marriage apparently directed 

 against consanguineous marriages are found even among many uncivilized 

 tribes of peoples. Undoubtedly the existence of these systems of mar- 

 riage in human society has had some influence in shaping the methods 

 which have been adopted by animal breeders, but at most the influence 

 has been small. The most potent factor in livestock practice has un- 

 doubtedly been the type of results which has been attained by following 

 one system or another, and the general utility which the given system 

 has in the hands of the average breeder. With respect to the degree of 

 kinship permitted in matings there are three general systems of breeding: 

 out-breeding, in which consanguinity is avoided as much as possible; 

 line-breeding, which is based upon matings of moderate blood relation- 

 ship; and inbreeding, which is based upon matings of animals closely akin 

 to each other. Each of these methods of breeding will be discussed below. 

 Inbreeding. Specifically inbreeding is a system of breeding in which 

 sire is bred to daughter, dam to son, or brother to sister. It is, therefore, 

 based upon the closest possible types of mating. This system of breeding 

 naturally has had its origin in the desire to intensify the blood of notably 

 superior individuals. The most used form of it, perhaps, is that in which 

 a famous sire is bred to his daughters and even at times to the second 

 generation of daughters which have been produced by inbreeding. The 

 method of inbreeding has been particularly useful in fixing types in the 

 early, formative period of the breed. It was the powerful tool which 

 that great breeder of the eighteenth century, Robert Bakewell, employed 

 in the improvement of horses, cattle, and sheep; and with astonishing 

 success. Evidently at that time the popular prejudice existing against 

 inbreeding was even stronger than it is today, as we may judge from 

 the statements of Culley written in 1794. 



The great obstacle to the improvement of domestic animals seems to have arisen 

 from a common and prevailing idea amongst breeders that no bull should be used in 

 the same stock more than three years, and no tup more than two; because (say they) 

 if used longer, the breed will be too near akin, and liable to disorders; some have im- 

 bibed the prejudice so far as to think it irreligious; and if they were by chance in posses- 

 sion of the best beast in the island, would by no means put a male and female together 

 that had the same sire, or were out of the same dam. Mr. Bakewell has not had a 

 cross for upward of twenty years; his best stock has been bred by the nearest affinities; 

 yet they have not decreased in size, neither are they less hardy, or more liable to 

 disorder; but, on the contrary, have kept in a progressive state of improvement. 



Culley might have written in the twentieth century, for even today 

 inbreeding is popularly blamed for a variety of ill effects. Of these we 

 have discussed decrease in fertility and vigor somewhat, and have reached 

 the tentative conclusion that inbreeding of itself does not always result 

 in diminished vigor and fertility, and therefore in all probability does 



