230 INBEEEDINa AND OUTBREEDING 



high degree of dominance. Among them may be men- 

 tioned the peculiar type of dwarfing known as achondro- 

 plasty, and the various digital malformations termed 

 medically brachydaetyly, Polydactyly and syndactyly. 

 Evidence of complete dominance is probably better in 

 these than in any other cases, but in view of the many 

 instances where subsidiary factors enhance or diminish 

 the expression of a primary factor, it seems decidedly 

 unwise to follow Davenport and to recommend marriage 

 with unaffected members of such families with the assur- 

 ance that the latter cannot transmit the trouble which 

 afflicts their relatives. If this advice could be accepted in 

 good faith, the inheritance of dominant traits, whether 

 disagreeable or desirable, would have little interest. They 

 would stand revealed in those possessing them; ithey alone 

 could transmit them. But this is not the whole truth. 

 Some of the so-called dominant characters in man are ab- 

 normalities which no one cares to see expressed in his or 

 . her children, and their dominance is imperfect or uncer- 

 tain. In many instances the records have been analyzed 

 hastily and carelessly; for example, hare-lip and cleft 

 palate, which is clearly a recessive condition in face of 

 the data, though passing as dominant in the various text- 

 books of heredity. In aU cases there is no guarantee that 

 the unaffected member of the stricken family is germinaUy 

 a pure normal. The family is one whose alliance is not to 

 be sought by those who have a proper pride in a normal 

 healthy posterity. Let us enumerate some of the troubles 

 that come in this category: Hereditary cataract, iehy- 

 thyosis or scaly skin, defective hair and teeth, diabetes 

 insipidus, Huntington's chorea — an affection of the 

 nervous system, imperfectly developed sex organs. 



