AN ESS A Y ON LONGEVITY. 51 



Spencer's chapters on the Laws of MultipHcation. 

 The amount of the species is made up by these 

 three factors : (i) the number born — i. e. the fertility; 

 (2) the average longevity (affected by early death-rate 

 and difficulties of development, see antea) ; (3) the 

 potential longevity. If a; case is taken where the 

 amount of food is increased, or the accessibility of 

 food increased, including in this all increased facili- 

 ties in carrying on the life, you must, to maintain the 

 balance of species and food, increase the amount of 

 the species either by increased fertility, by increased 

 average longevity, or by increased potential longevity. 

 It is of the last only that we have here to speak. 

 The relation of expenditure as antagonistic to lon- 

 gevity tallies with this necessity thus. Increased 

 accessibility of food, of the means of life, clearly 

 renders less personal expenditure necessary ; less 

 exertion is required in obtaining it, and may be less 

 in digesting it ; also less waste of material in main- 

 taining the temperature (for that condition may be 

 included in accessibility of food), and with this there 

 will be, according to our proposition (p. 47) increased 

 potential longevity. Thus the balance may be main- 

 tained through the antagonism of personal expendi- 

 ture and longevity. Should increased accessibility 

 of food produce increased generative expenditure, 

 as it may^ — though the potential longevity should, 



' Mr. Spencer clearly shews this in his chapter ' Coincidence of High 

 Nutrition and High Genesis.' 



E 2 



