44 INHERITANCE, VARIATION AND SELECTION. 



animals are mated there is little probability that the same dormant 

 defects will exist in both, but when both parents are from the same 

 stock the probabilities of the same defect existing in both are in- 

 creased, and the mating of these two may cause the dormant defect 

 to become a manifest one. Of all animals, man is the most vicious 

 in respect to his personal life. By immoderate indulgences in 

 intoxicants and narcotics, and by dissipation and excesses of all 

 kinds, man acquires a great variety of defects, both dormant and 

 manifest, and these defects are transmitted to his offspring. It 

 therefore happens that with man even a remote kind of in-and-in 

 breeding often results in insanity or degeneracy of some kind, and 

 much has been written about the evil effects of marriage between 

 cousins. Such evil effects, however, do not arise from the rela- 

 tionship itself, but from similar dormant defects inherited from 

 the same vicious ancestor some few generations back. 



In-and-in breeding is therefore the mating of animals having 

 identical characteristics, the result of which is to make manifest 

 what was before dormant, or to accentuate and fix what was before 

 mildly manifest and transient. The expression is usually applied 

 to the mating of closely related animals, but in future pages I shall 

 refer to marriage between persons inheriting similar characteristics 

 from different ancestors as a species of in-and-in breeding. 



PREPOTENCY. 



If the offspring of parents differing considerably from each 

 other be carefully examined, it will usually be found that they 

 resemble one parent more than the other. The power that one 

 parent has more than the other to impress the offspring is called 

 prepotency, and may exist in either the male or female. Usually 

 the male is more apt to be prepotent than the female, as in recip- 



