ON THE FOUR BEST PLUMS 



in following up the clues thus suggested that I 

 came to believe that the explanation of this va- 

 riation must be sought in heredity. 



I reflected that each normal organism has an 

 ancestry that takes in vast numbers of individ- 

 uals if we go back only a few generations eight 

 great-grandparents, thirty-two in the generation 

 before, and more than a thousand within ten 

 generations. 



How then could the descendant of such a gal- 

 axy of ancestors, carrying the potentialities of all 

 their traits, be otherwise than a complex organ- 

 ism not only different from either of its parents, 

 but different also from any single member of its 

 entire ancestral clan? 



It seemed also a reasonable enough assump- 

 tion that, where such a multitude of more or less 

 divergent traits are brought together and put in 

 conflict, the exact combinations of traits would 

 be different in the case of each successive off- 

 spring of any given pair of parents; so that no 

 two individuals of the same fraternity would be 

 precisely alike, any more than any one of them 

 would be precisely like any individual ancestor. 



In a word, then, it seemed obvious to me that 

 the individuals of a species constitute a variable 

 and plastic race, in virtue of their diversified an- 

 cestral strains. 



[45] 



