Evolution of Intelligence 73 



Does natural longevity follow variations in 

 the average age at which a race of animals re- 

 produces, or does the average age at which they 

 reproduce follow variations in natural longevity? 



The question is fair. The facts of evolution 

 say that the two go together, and logic requires 

 that one be the leader and the other the follower. 

 We know that reproduction is spread over con- 

 siderable parts of the lives of parents, and that 

 any kind of circumstances may limit the sur- 

 vivors to offspring produced at early or late parts 

 of life. We also know that tribes and races of 

 men at many times in the past have adopted 

 marriage customs which changed the average age 

 at which the race reproduced. Such changes 

 usually had their foundation in some military 

 expediency, and certainly were not changes fol- 

 lowing or caused by previous varitions in natural 

 longevity. In other words, we know definitely 

 that changes in the average age at which a race 

 of animals reproduces may be, and frequently 

 are, wholly independent of previous changes in 

 the longevity of the individuals of the race. 



If changes in longevity follow changes in the 

 average age at which reproduction takes place, 



