The Laws of Heredity. 163 



In the first place, if the author, basing his judgment entirely on 

 the fact of mental alienation, proposes thence to draw a conclusion 

 covering the whole question of heredity, physical as well as moral, 

 he makes so great a mistake in logic that the mere statement is a 

 sufficient condemnation. It would be too arbitrary to rely on a 

 single characteristic, for the heredity of insanity does not include 

 that of the muscular system, of the features, of the complexion, or 

 the apparatus of organic life. 



But if, as is probable, he means to speak only of mental here- 

 dity, the fault of his reasoning, though less grave, is still very serious. 

 The heredity of mental affections is only one of the forms of 

 psychological heredity, and it is not legitimate to argue from one 

 to all. To derive from parents a morbid predisposition which will 

 hereafter lead to mania, monomania, hallucination, or dementia, 

 by no means necessitates the inheritance of their entire psycho- 

 logical constitution, their character, their genius, their scientific 

 and artistic aptitudes, their memory, passions, or sentiments ; facts 

 prove the contrary. In very many cases the cause of mental 

 disease is altogether physical a lesion of the brain or of some 

 other organ ; and nothing justifies the assertion, that as these 

 lesions are inherited, therefore the whole mental dynamism is also 

 inherited. 



Thus the arguments drawn from mental pathology have not so 

 wide a range as Baillarger assigns to them. But if they are 

 insufficient to prove that heredity in the same sex is more frequent 

 than cross heredity, they do, however, prove that it is of frequent 

 occurrence. 



We now cite from history some well-established instances of this 

 form of heredity. 



HEREDITY FROM FATHER TO SON. 



FATHER. SON. 



Nicomachos . . . Aristotle 



Scipio (Publius Cornelius) Scipio (Africanus major) 



Vespasian . . . Titus 



Verus (^Elius) . . Verus (Lucianus) 



Pepin d'Heristal . . Charles Martel ' 



Charles Martel . Pepin the Short 



