CHAPTER VI 



INBREEDING EXPERIMENTS WITH ANIMALS 



AND PLANTS 



Doubtless discussion has been rife since the dawn of 

 civilization as to the actual effect of more or less close 

 intermating in the various breeds of domestic animals, 

 since stock-raising was one of the earliest arts and was 

 brought to a high degree of perfection by the ancient 

 Semitic nations. One may surmise, from the rules they 

 made against the marriage of near relatives, that the pro- 

 ponents of cross breeding had the best of the argu- 

 ment ; but it is hardly likely that their practice was any- 

 thing more than rule-of -thumb adopted after a variety of 

 casual observations. At any rate, controversy is still spir- 

 ited, and one reads the opinion of stock-breeding authori- 

 ties without arriving at any definite knowledge of the 

 problems. Their results are confusing, and the only con- 

 clusion one may reach from their perusal is the wholly 

 unsatisfactory one that close mating, as a system of breed- 

 ing, has both advantages and disadvantages. Without 

 question, it has had great value in fixing certain desirable 

 types. Some breeds, as a whole, and many individual 

 herds, owe their uniformity in conformation and perform- 

 ance in a large measure to close inbreeding accompanied 

 by rigid selection. At the same time, it must be recog- 

 nized that certain evil effects may result from close inter- 

 mating. These effects have been frequently expressed in 

 lessened constitutional vigor, greater susceptibility to 

 disease, reduced fecundity, and, in some cases, even in 



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