CHAPTER IX 



THE EFFECTS OF INBREEDING 



WHAT is the probable source of the 

 evil effects which have been fre- 

 quently observed to follow in- 

 breeding? 



By inbreeding we mean the mating of closely 

 related individuals. As there are different de- 

 grees of relationship between individuals, so 

 there are different degrees of inbreeding. The 

 closest possible inbreeding occurs among plants 

 in what we call self-pollination, in which the 

 egg-cells of the plant are fertilized by pollen- 

 cells produced by the same individual. A simi- 

 lar phenomenon occurs among some of the 

 lower animals, notably among parasites. But 

 in all the higher animals, including the domes- 

 ticated ones, such a thing is impossible because 

 of the separateness of the sexes. For here no 

 individual produces both eggs and sperm. The 



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