Longevity 187 



members living to over eighty }< T ears of age. 

 When these were traced back they were 

 found to have come from three or four genera- 

 tions of late reproducing stock. Men of great 

 intellectual ability also usually live longer 

 than ordinary people, and it has been pre- 

 viously shown that they are from successive 

 generations of old parents. 



There is another reason why late reproduc- 

 tion is conducive to longevity by preventing 

 early death, and this is immunity. A person 

 who is attacked by disease and overcomes it 

 is more or less immune to subsequent attacks 

 of the same kind, and the older he is the more 

 likely he is to have acquired this immunity. 

 Resistance to disease involves the expenditure 

 of energy, and it has been shown before that 

 the expenditure of energy through organs 

 causes a concentration of energy in the 

 organs through which the expenditure oc- 

 curred. Also, that a similar concentration 

 appears in offspring produced after the origi- 

 nal concentration occurred. From this it 

 would appear that immunity may be inheri- 



