72 Evolution of Intelligence 



Let us go back to that common ancestor of 

 man and ape and picture to ourselves some of 

 the steps by which man was evolved. That early 

 ancestor was of low intelligence, reproduced at 

 an average age of some twelve or fifteen years 

 from birth of parent to birth of offspring, and 

 normally lived some twenty or thirty years. Lit- 

 tle by little as the ages went by, this animal re- 

 produced at later and later average ages, rose 

 step by step in intelligence and lived greater 

 and greater lengths of time. 



These three things, average age at reproduc- 

 tion, inherited powers, and normal longevity, are 

 indissolvably linked together and an examination 

 of the relationship between them shows how they 

 are linked and how they may be brought under 

 human control. Between natural longevity and 

 the average age at which reproduction takes 

 place, the relationship is direct, as far as it is 

 possible to determine by facts available. In the 

 different races of men, and in different species of 

 lower animals, the natural longevity is approxi- 

 mately twice the average age at which reproduc- 

 tion takes place. 



