Exceptions to the Law of Heredity. 199 



never more than partial : for even where heredity does not transmit 

 the individual characters, it at least transmits the specific characters. 

 The question, therefore, is not to ascertain whether heredity is a 

 biological law, but whether that law is absolute. As the excep- 

 tions are no less unquestionable than the law, and as they must 

 necessarily have a cause, there can be but two hypotheses. 



a. We may hold that there is in nature an essential, permanent 

 cause, of which the phenomena of spontaneity are the effects in 

 other words, that the biologic fact of generation is governed by 

 two laws, one of spontaneity, the other of heredity, the law being 

 only the expression of what is constant in the production of 

 phenomena the invariable relation between cause and effect. 

 This is the thesis maintained by Dr. Lucas. 



/3. Or we may say that the causes of spontaneity are only acci- 

 der'.al; that it is never more than a chance, the result of the 

 fortuitous play and concurrence of natural laws ; but that it is not 

 the effect of any distinct and special law. On this theory there 

 would be one law of heredity with its exceptions, not two laws, the 

 one of heredity, the other of spontaneity. This second thesis is 

 our own. But before demonstrating it we must consider the oppo- 

 site opinion. 



Of this Dr. Lucas has given a full exposition, applying to it 

 philosophic principles. He holds that every living being, con- 

 sidered in its origin that is, in its generation is the product of 

 two laws, which he places both on one plane and on the same 

 level. One is the law of spontaneity, by which nature ever 

 creates and invents. The other is the law of heredity, by which 

 nature ever imitates and repeats herself. The former is the 

 principle of diversity, the latter of resemblance. If the former 

 stood alone, there would be in the world of life nothing but 

 differences infinite in number; if the latter stood alone, we 

 should have nothing but absolute resemblances. But taken 

 together, these two principles explain how all living things of the 

 same species may at the same time resemble one another in their 

 specific characteristics, and differ in their individual characteristics. 



If we regard the question here proposed from a metaphysical 

 point of view, it cannot be denied that a difficult, and probably an 

 insoluble, problem arises. In the middle ages, it was hotly 



