INTRODUCTION 9 



of evolution in general is perfection of adaptation to the conditions of 

 life as they happen to be at any particular time. Many a highly 

 perfected creature has reached the goal of its evolutionary course 

 only to perish because it was too highly perfected for a particular 

 environment and could not withstand the hardships incident to radi- 

 cally changed world-conditions. Many evolutions therefore have 

 been completed, while others are still awaiting the opportunity to 

 speed up toward a new goal. 



7. Evolution is therefore not entirely a thing of the past. Obvi- 

 ously some species, including Man perhaps, are nearly at the end 

 of their physical evolution, but there are always certain generalized 

 plastic types awaiting the next great opportunity for adaptive speciali- 

 zation. — Ed.] 



