20 HEREDITY AND INHERITANCE 



through six generations, and the pathologist Bouchut (cited 

 by Ziegler) refers the origin of the evil to the rage of an ancestor, 

 who terrified his wife during her pregnancy with the wish that 

 the fingers with which she had plucked an apple against his 

 orders might be cut off ! Apart from the story's quaint sugges- 

 tion of a much older episode, it requires but an elementary 

 knowledge of the facts of heredity and inheritance to convince 

 us that the alleged cause was inadequate to account for the 

 effects. 



In two hundred families tainted with a predisposition to 

 bleeding (haemophilia), which is partly due to inborn weakness 

 in the walls of the blood-vessels, Grandidier * found six hundred 

 and nine male " bleeders " and forty-eight female " bleeders." 

 It is a problem of inheritance (and partly perhaps of sexual 

 physiology) to discover why the disease should predominate 

 in males ; and the interest of the problem is enhanced by the 

 fact that the disease rarely passes from father to son, but usually 

 from a male (or female) parent, through an apparently una^eded 

 daughter, to a grandson. In short, the female offspring of 

 bleeders hand on the taint predominantly to male offspring, 

 without themselves showing the disease. 



De CandoUe f reported from American statistics that thirty 

 per cent, of the children of congenitally deaf-mute parents were 

 deaf-mute, but that the percentage was fifteen when only one 

 parent was congenitally deaf-mute. It is a problem of heredity 

 to interpret the greater frequency of inheritance when both 

 parents were affected. 



While there is much and justifiable uncertainty in regard to 

 the origin of what are called instincts, there is no doubt that an 

 organism's inheritance often includes the power of carrying out 

 a complex series of operations without experience and without 

 education when the appropriate stimuli occur. 



* Grandidier, Die HcBfnophilic (1876). . 



I De CandoUe, Arch. Sci. Phys. Nat. xv. p. 25, cited by Ziegler (1886). 



