Exceptions to the Law of Heredity. 201 



place with such ideal simplicity. In the first place, there are 

 ordinarily in the act of generation two sexes, and consequently 

 two antagonistic heredities ; this is the first cause of diversity. 

 There are, furthermore, accidental causes which are in action at the 

 very moment of generation ; and this is another cause of diversity. 

 Finally, there are external and internal influences subsequent to 

 conception. 



It is clear, says M. Quatrefages, that in every procreation the 

 parents import influences which may be ranged in the following 

 three orders of facts : their characters may be similar, or opposite, 

 or different. In the first case there will be a persistence or an 

 augmentation of the characters transmitted ; in the second a 

 diminution of them, or a reciprocal neutralization. Suppose two 

 parents, one of them presbyopic and the other myopic ; the child 

 will have the chance of good sight, in consequence of the conflict 

 of opposite influences. In the third case, if the characters are 

 simply different, the product is the resultant of the father and 

 mother ; that is to say, a new character appears, differing from the 

 other two, though due to heredity. Thus, among animals, when 

 the parents are of uniform different colours, the progeny very often 

 have the skin mottled, parti-coloured, or striped, and consequently 

 very different from that of the father and mother. 



Thus heredity, in virtue of its fundamental law, may play the 

 part of this force of spontaneity devised by Lucas. We hold that 

 there are cases of spontaneity which result from natural causes; 

 we do not admit a law of spontaneity. Indeed Lucas's hypothesis 

 is contradictory. To understand how little spontaneity possesses 

 the character of a law, we need but observe that a law is identical 

 with the phenomena it governs, since it is only the expression of 

 what in them is permanent and essential, so that it enables us to fore- 

 tell them. If the law of heredity may be supposed to be alone in 

 operation, without disturbing influences, it may be predicted that 

 the product will resemble one of the parents, or both. But sup- 

 pose a law of spontaneity, no prediction or provision is any longer 

 possible, since anything whatever may occur where diversity is the 

 rule. This is permanent disorder. But it is impossible from this 

 to deduce a law. A law is declared by a process of abstraction 

 and generalization, which cannot be applied to cases which are 



