CHAPTER II. 



THEORIES OF HEREDITY AND VARIATION. 



The persistency with which heredity acts in preserving the 

 peculiarities of faces and individuals through many generations, 

 and the ever present variations of these peculiarities have given 

 rise to many diverse theories to account for their relationship to 

 each other. "Like produces like" is a very old saying, and when 

 we consider that the offspring comes directly from the parent, it is 

 difficult to conceive that it would be anything other than that from 

 which it came. We can imagine how the same thing may at cer- 

 tain times take different forms, but not how one thing may become 

 another thing unless it be through the total destruction of the first 

 thing. Thus we may have water now as ice, again as steam, and 

 at another time as snow, but under each and every form it is water. 

 It can be transformed into some other substance only by decom- 

 position and the recombination of its constituent elements with some 

 other elements. Likewise a being descended from a human being 

 can be no other than human. He can be transmuted into a plant 

 only by disintegration and reabsorption. Inheritance being simply 

 an expression for the fact that the deriven is like that from which 

 it is derived, is self-evident and needs no explanation. Variation, 

 on the contrary, being something different from what is apparently 

 self-evident, demands an explanation of when, where and how it 

 arises. 



VARIATION DEFINED. 



The word "variation," as used in biology, represents two dis- 

 tinct conditions or operations : First, the appearance of an entirely 



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