PEOPLE FOR THE EARTH 589 



these ; but in the end that would probably be the cheapest thing 

 to do. After all, they do continue to live, and those of us who 

 are doing useful work have to support them, whether through 

 charity or through taxes or through being robbed indirectly. 



423. Controlling the future. The most valuable qualities of 

 mankind are possible only in civilized communities ; but civili- 

 zation brings its dangers to the race. We cannot, on account of 

 these dangers, throw overboard all our gains and return to 

 natural selection. That would only make the beast triumph. 

 The only hope lies in gathering more knowledge and applying it 

 to our practical problems. 



The application of our knowledge of heredity to human affairs will 

 probably be along the line of showing us what types of marriages are 

 Hkely to produce offspring that are undesirable in one way or another. 

 We already know that certain abnormalities of physical structure or of 

 mentality are transmitted in a definite way, and we are therefore war- 

 ranted in counseling men and women who belong to families that show 

 these characters not to marry others of similar stock. In the course of 

 time we shall no doubt develop certain standards of fitness for marriage 

 which will be enforced largely by the same kind of public opinion and 

 tradition as now distinguishes the customs of different peoples. 



In the end the earth will belong to that race which can best 

 use its intelligence to advance civilization and to overcome its 

 dangers— disease, poverty, ignorance, and war. 



PEOPLE FOR THE EARTH 



1. The earth's population is constantly changing 



Some species are increasing numerically 

 Some species are diminishing 

 Migrations change the balance of species 

 Migrations carry parasites into new territory 

 Species have died out entirely in the past 

 Mutations give rise to new species 

 Obscure species rise to prominence 



2. Man the dominant species of life today — especially civilized man 



Civilizations in the past have flourished and decayed 



