In-and-in-breeding 157 



than those parts which are most highly developed 

 in the female. The improvement of domesticated 

 fowls depends upon the transmission of desired 

 characteristics which have been produced through 

 the action of this law or fact of variation. 



In-and-in-breeding. This term is often used 

 in a rather loose sense to indicate the breeding 

 together of animals which are more or less closely 

 related. It is generally used, however, to indicate 

 the breeding together of animals that are closely 

 related for several successive generations; and in 

 this sense it is used in this discussion. As breeders 

 have not agreed on an exact definition of in-and-in- 

 breeding, there is a considerable difference of opin- 

 ion as to just what the term implies. Some breeders 

 hold that the term implies only the mating of animals 

 of the closest relationship, while others strenuously 

 maintain that more distant relationship should be 

 included. It is held by some that breeding together 

 animals which have a more distant degree of relation- 

 ship than that known in the human family as aunt 

 and nephew or uncle and niece, should not be recog- 

 nized as coming within the meaning of this term. 

 On the other hand, others are emphatic in including 

 more remote relationship. 



In-and-in-breeding has played a most important 

 part in the formation of breeds and also in the 

 improvement of breeds that were well established. 

 As variation and selection enable the breeder to 



