244 WORLD-POWER AND EVOLUTION 



there remain many facts which indicate that extremes of heat and 

 cold, dryness and moisture, are somehow associated with pro- 

 nounced changes in the form and function of the organs of the 

 body. That single fact, if it be a fact, is more important than all 

 else that we have here discussed. Part of its importance lies in 

 that it opens up the possibility that some day mankind may learn 

 not only how to select the best variations in a given plant or 

 animal, but how to cause a great number of widely diverse muta- 

 tions from among which he may select. In all this the human race 

 is merely one among the species of animals. For aught we know, 

 his migrations and the many new and artificial conditions to which 

 he subjects himself may be altering some of his most deep-seated 

 qualities. We spend millions in the attempt to improve plants and 

 animals. Is it not time that we learned how the highest of all an- 

 imals is being changed and how his future evolution may be 

 directed along the right path.'* 



