180 EVOLUTION AND GENETICS 



species, they furnish clear-cut characters that are 

 sharply separated from normal structures, and hence 

 can be traced through successive generations. It may 

 properly be claimed that in studying the inheritance 

 of each defect we are also studying the inheritance of 

 a normal character that forms the other member of 

 the contrasted pair. This statement, however, calls 

 for an important reservation ; for, all that we mean 

 by such a contrast is that the "normal" is not the ab- 

 normal. We do not in reality know anything more 

 than this. This relation is, however, inherent in all 

 Mendelian contrasted character-pairs, unless mem- 

 bers of an allelomorphic series are somewhat more 

 specific. 



The presence of malformations of the body in 

 human stocks is not supposed to be due to a greater 

 tendency in the human species than in other species 

 to produce, de novo, defective mutants, but rather 

 to be due in man to the preservation of individuals 

 having such characters and allowing them to marry, 

 or at least not preventing them from mating. The 

 higher ethical standards of man lead him to preserve 

 human life, and in the absence of severe competition 

 (through which the maladjusted would go under) 

 the defective child reaches maturitv. 



If the new character is recessive its gene may 

 become widely disseminated in the human germ- 

 material before two individuals each with the reces- 

 sive gene mate. One-fourth of their offspring will 



