Longevity 189 



of young parents than in the offspring of old 

 parents. This was investigated in human 

 beings with the following results : 



Fecundity oj Offspring Influenced by Age of Parents 



100 sons of young fathers had 568 children 



100 sons of old fathers had 309 children 



The "young fathers" were those 30 or less, 

 while the "old fathers" were those 40 or 

 more. While a difference is to be expected, 

 the size of the difference is surprising. If the 

 tabulation were extended to 1000 instead 

 of 100 families, the percentage of difference 

 would probably be less. There is, however, 

 much difficulty in finding large numbers of 

 heads of families who were sons of men over 

 40 years of age. More than one thousand 

 families were investigated to find the one 

 hundred whose heads were sons of men over 

 forty. 



The production of germ cells appears to be 

 a compound of rate of cell division and func- 

 tion performed, — a conjoint action between 

 breeding and working cells. The rate of cell 



