HUMAN AND ANIMAL EVOLUTION CONTRASTED 37 



of his parents. It is necessary, however, clearly 

 to distinguish between the two types of inheritance, 

 and to recognize that they are brought about by 

 a different set of forces and controlled by differ- 

 ent laws. If for the one type of tranference we use 

 the term '' organic" or '^ germinal heredity," and 

 for the other ''social heredity," there can be no con- 

 fusion of meaning and our use of the terms in this 

 sense is perfectly defensible. 



Its Certainty of Action. — We next notice that social 

 heredity is just as sure in results as organic he- 

 redity; indeed, it is sometimes more sure. Organic 

 inheritance has always been recognized as a matter 

 of great uncertainty. Even though the parents both 

 have black eyes, it is by no means sure that the off- 

 spring will have the same. Some features are indeed 

 fairly certain to be inherited by the children, for we 

 may be reasonably confident that the child will have 

 arms and legs, inherited of course from its parents ; 

 though occasionally this rule is broken, for armless 

 children are sometimes born from normal parents. 

 In regard to the countless minor characters there 

 seems to be apparently no definiteness in the result. 

 Part of this doubtless may be due to our ignorance, 

 and we must believe that some day these obscure 

 facts may be made more clear. But it is certain that a 

 child's inheritance is still problematical, even though 

 his line of germinal inheritance is fixed. History i« 

 filled with instances of children departing wirl'^iy 

 from their parents, and cases will occur to the mind 

 at once of the "black sheep" in the family of excep- 

 tionally good inheritance, or of unexpected "white 

 sheep" in a family made up mostly of the black 

 variety. With an identical inheritance two brothers 



