98 t'hje; coming of man 



aptations from a whale, there is not much left." The story 

 of evolution is a history of successful adaptations. 



In every age and stage of our evolution some organ has had 

 its special time for rapid change and improvement. Then the 

 pressure or urge passes over to some other part, as we have 

 seen in our study of the sequence of dominant functions. 

 The essential features of the organ now set and become rela- 

 tively fixed; all further changes are slight. Nearly all the 

 organs of the human body have acquired fairly definite form 

 and structure, and have changed but slightly during the last 

 million years. Changes now are mostly limited to the " silent 

 areas " of the cerebral cortex. There is a time for everything 

 and '' opportunity knocks but once." Yet it is all one process, 

 " the history of the ever-advancing victory of spirit over mat- 

 ter," as von Baer said. 



We have spoken of conformity to environment as if it were 

 merely a stamp impressed upon receptive and passive material. 

 This is not correct. The adaptation consists in a reaction of 

 the living being, stimulated by external forces. The reaction 

 or response to the stimulus differs according to the character 

 of the responding animal or man and hence may vary greatly. 

 I may give the same kick to a stone, a sheep or a bull-dog; 

 the response will be quite different. The more highly de- 

 veloped and complex the animal, the more varied and less pre- 

 dictable its response. Sloth, squirrel and ape are all adapted 

 to an arboreal environment, but they have reacted very dif- 

 ferently; all three have conformed but in different ways and 

 to different degrees, the sloth apparently the most completely 

 of all. 



There is such a thing as over-adaptation where the animal 

 or man has so completely adapted itself to one set of condi- 

 tions that change and readaptation to a new environment is no 

 longer possible. If its environment changes, as it always does, 

 or if it is compelled to seek a new environment, it is at a dis- 

 advantage and probably disappears. Large size usually shows 

 that conditions in a certain age and place have been favor- 

 able and adaptation complete. If climate and food-supply 



