CHAPTER XIII 



VARIATION AND EVOLUTION 



Through the facts of heredity we have reached a new 

 conception of the individual. Hitherto we have been 

 accustomed to distinguish between the members of a 

 family of rabbits like that illustrated on Plate I. by assign- 

 ing to each an individuality, and by making use of cer- 

 tain external features, such as the coat colour or the mark- 

 ings, as convenient outward signs to express our idea that 

 the individuality of these different animals is different. 

 Apart from this, our notions as to what constituted the 

 individuality in each case were at best but vague. Men- 

 delian analysis has placed in our hands a more precise 

 method of estimating and expressing the variations that 

 are to be found between one individual and another. In- 

 stead of looking at the individual as a whole, which is in 

 some vague way endowed with an individuality marking 

 it off from its fellows, we now regard it as an organism 

 built up of definite characters superimposed on a basis be- 

 yond which for the moment our analysis will not take us. 

 We have begun to realise that each individual has a defi- 

 nite architecture, and that this architecture depends 



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