234 INBREEDING AND OUTBREEDINO 



of genius are numerous. Only occasionally is the proper 

 combination brought together. The factors exist in the 

 population at large, distributed in part to one individual, 

 in part to another, but in the main the combinations make 

 but for mediocrity. Only on a rare occasion is a favored 

 one so showered with these gifts that he stands out 

 supreme among his fellow-men. 



No one knows what the component parts of these desir- 

 able qualities are, or can distinguish by external traits the 

 individual who carries them, but a knowledge of the opera- 

 tion of Mendelian heredity enables one to say in a general 

 way what ought to occur under given conditions with the 

 same confidence as when dealing with similar indefinite 

 qualities in the lower animals. Close selection, inbreeding, 

 tends toward the production of gametic purity with mathe- 

 matical precision. Does any one doubt but that close 

 breeding in families which have shown superior civic value 

 tends to concentrate, to purify, in genetic terms to render 

 homozygous, the particular factorial combinations which 

 cause this superior endowment? Will any one deny there 

 is a real privilege in being allowed to marry into a family 

 of proved worth, or a real reason for that family to scru- 

 tinize carefully the ancestry of one who asks to become 

 allied with it? 



We have seen how when certain hereditary factors 

 have been brought together by the proper breaks in link- 

 age, they tend to be transmitted together in the same man- 

 ner as did the previous set of coupled factors. This 

 same idea, followed to its logical conclusion, is a great 

 help in visualizing the inheritance of capacity. The indi- 

 vidual who owes his capacity to a complex which mav be 

 represented graphically by the linked series AbCd-aBcD 



