4Si HEREDITY AND ENVIRONMENT 



tion lies in this very fact that it brings about 

 the commingling of distinct lines and thereby 

 makes every individual different from every 

 other one. The entire history of past evolu- 

 tion testifies to the value of this process, al- 

 though it causes the gardener, the breeder, the 

 eugenicist serious trouble. But the gardener 

 can propagate his choice fruits by budding and 

 grafting, the breeder can for a time preserve 

 his choice stock by close inbreeding, but the 

 eugenicist cannot shut out the influence of for- 

 eign blood, and it is well that he cannot for 

 if he could do so the progress of the race 

 would probably soon come to an end. 



In the human species the only absolute bar- 

 rier to the intermingling of races is geographi- 

 cal isolation. Every human race is fertile with 

 every other one, and though races and nations 

 and social groups may raise artificial barriers 

 against interbreeding we know that these arti- 

 ficial restraints are frequently disregarded and 

 that in the long run amalgamation does take 

 place; and in general the farther amalgama- 

 tion progresses the faster it goes. In Aus- 



