160 MAN --AN ADAPTIVE MECHANISM 



the easily excited antelope, the spider monkey and 

 certain dynamic inhabitants of the sea, such as the 

 trout and the salmon, apparently hoard a supply of 

 convertible energy far in excess of the routine needs of 

 feeding and multiplying. 



As for man, who is just emerging from an environ- 

 ment in which muscular efficiency has been of para- 

 mount importance to survival, in fighting and searching 

 for food, in fleeing from enemies, in building safe havens, 

 in pursuing and winning mates, and in accomplishing 

 procreation, the need for variation in dynamic expendi- 

 ture is obvious. 



Variation in Rate of Energy Transformation in the 

 Individual 



The rate of energy transformation varies not only in 

 different species of the animal kingdom, but in individ- 

 uals of the same species, and in different periods of the 

 life of the individual. Thus, peoples who have lived 

 long in an environment of natural plenty, who have had 

 to exert themselves but little to make a living, show 

 few and simple reactions as compared with the more 

 strenuous members of continually warring communities. 

 To compare the natives of our tropical plantations, or 

 of the fertile valley of the Nile, with the dynamic- 

 tempered Jew and other urban-born and business- 

 disciplined inhabitants of seething cities is like com- 

 paring the turtle with the spider monkey. 



In the life cycle of the individual organism there are 

 both long and short periods of increased activity to 

 which the organism must become adjusted. The out- 

 put of energy must meet the varying requirements of 



