234 PHYSICAL BASIS OF CIVILIZATION 



reproduction between members of the new species, 

 and either absolute barrenness or that partial bar- 

 renness which results in the reproduction of sterile 

 offspring from the interbreeding of the new species 

 with other varieties of the parent species. 



This mystery Darwin's theory leaves unexplained, 

 but if research should hereafter confirm the opinion 

 expressed in the third paragraph above, then would 

 the said theory be thereby demonstrated beyond 

 reasonable doubt. 



