WHAT EVOLUTION IS 129 



selves, they, like their parents, pro- 

 duced whites as well as blacks. 



If, now, we examine the whole 

 breeding series from the standpoint 

 of the purity of the germ, we shall 

 find reason for the occurrence of the 

 proportions given. This can be done 

 best by reference to the diagram on 

 page 131. Here it will be seen that 

 the source of the descendent stock 

 is the pair of guinea pigs, one white 

 and the other black, represented in 

 outline at the top of the page. Which 

 of the two is male and which female 

 makes no difference so far as the final 

 outcome is concerned. The white one 

 is supposed to have been derived 

 from a pure white stock, that is, 

 from a stock which in all its pairings, 

 within its own bounds, produced 

 nothing but white individuals. Hence 

 the white pig must be assumed to 

 have come from an tgg containing a 



