CHAPTER I 



THE DUALITY OF INHEEITANCE 



AT the outset we may with profit inquire 

 /-% what is meant by heredity. When a 

 •^ -^^ child resembles a parent or grand- 

 parent in some striking particular, we say it 

 inherits such-and-such a characteristic from 

 the parent or grandparent in question. By 

 heredity, then, we mean organic resemblance 

 based on descent. 



Resemblances due to heredity may exist even 

 between individuals not related as ancestor and 

 descendant, as for example between uncle and 

 nephew. Here the resemblance rests on the 

 fact that uncle and nephew are both descended 

 from a common ancestor, and they resemble 

 each other simply because they have both in- 

 herited the same characteristic from that an- 

 cestor. This form of inheritance is sometimes 

 spoken of as collateral in distinction from direct 



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