110 THE NATURE OF LIFE 



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including changes in eye-color, shape of 

 wings and body, hairiness, and partial or 

 complete loss of organs. 



In order to control these mutations we 

 must discover the physicochemical fac- 

 tors on which they depend. If such con- 

 trol can be established we shall be able to 

 create new species. The aim of modern 

 biology is to accomplish this, just as we 

 control growth, metabolism, irritability, 

 and other life processes. 



Upon man's control of nature rests all 

 our civilization. The last and most dif- 

 ficult step in the conquest of nature is 

 the control of life. This offers so much 

 promise that no effort is too great to 

 consecrate to it, and each step forward 

 is of fundamental importance for human 

 welfare. 



