THE LESSON OF HEREDITY 



two ancestors who would be doubly represented in the 

 curtailed generation would doubly represent exactly 

 the same focalized group of tendencies as would be 

 represented by any other two persons. And yet we 

 know that consanguineous unions do make a difference 

 in practice. 



We have come to another stumbling block. But the 

 explanation is not far to seek, though it lies partly out- 

 side the domain of heredity. We have said that every 

 individual comes into the world with possibilities 

 representing the sum of all the tendencies of all its 

 ancestors. This formula is certainly at once correct and 

 comprehensive. It would be a misuse of language to 

 speak of inheritance of a tendency not represented in 

 some ancestor, near or remote. But the same formula 

 does not represent fully the personality of the same 

 individual when he has grown to adult life, for then we 

 must say, The sum of all the tendencies of all ancestors 

 plus certain qualities developed in the present genera- 

 tion through contact with a definite environment. And 

 these acquired qualities we are bound to believe, not- 

 withstanding the dissent of a certain school of modern 

 biologists, are represented in the sum of tendencies 

 which this individual transmits to his progeny. It is 

 as if an ancestral estate received additions with each 

 generation of holders. Only it must be remembered 

 that the additions are not necessarily improvements. 

 There are minus as well as plus quantities in our 

 problem of heredity. 



Not only may new tendencies be thus added gen- 

 eration after generation, but the old tendencies may be 



1305] 



