52 EX VIRIBUS VIVIMUS. 



cceteris paribus, be diminished — yeX that this relation 

 is duly consistent with the requirements of the case 

 is seen in the fact that increased generative expendi- 

 ture means increased fertility ; and so the equation 

 Fertility x Average Longevity x Potential Longevity 

 = Food X c is maintained ; the diminished potential 

 longevity being directly corrected by the correspond- 

 ingly increased fertility. It is not necessary to shew 

 that the correspondence is true for diminished food, 

 since it is sufficiently obvious. 



Next as to Evolution or Individuation. Increased 

 food does not at first sight appear to go with high 

 individuation, and thus admit of the balance in the 

 equation being struck by the consequent increase of 

 potential longevity. Low organisms feed on abun- 

 dant and widely dispersed food, and fulfil the re- 

 quirements of the equation by their increased fertility. 

 But increased food, in the sense of more nutritious 

 food, and more of it for each individual, does go with 

 increased individuation, and at the same time dimi- 

 nished fertility accompanies increased individuation ;' 

 hence the balance has to be made up out of the 

 other two terms, average and potential longevity, 

 and we have seen that it is so made up by the re- 

 lation of individuation and longevity, deduced above: 

 Then as to the effect of decrease of food ; by absolute 

 diminution of food accessible to the species, you do 



' This must be accepted from Mr. Spencer, who fully demonstrates 

 that this is the case. 



