AN ESS A Y ON LONGEVITY. I 27 



excessive expenditure with the least luxury, where 

 regularity and temperateness are innate character- 

 istics, will be that state of civilization most favourable 

 to longevity. It may be supposed by some that 

 since the tendency of civilization at present is to 

 call out increased mental expenditure, that even 

 when the other conditions of longevity are complied 

 with, future men will rather lose than gain in lon- 

 gevity. This, however, depends upon the assumption, 

 which we have no ground for allowing, that the 

 structural capacity for such requirements will not 

 increase simultaneously. There is every reason to 

 believe that it will — that it is so doing. We are now 

 in the midst of a struggle — in a transition state — which 

 is really causing a survival of the fittest, operating 

 chiefly through the emulation of communities, but also 

 on individuals, and by means of this struggle greater 

 mental power is being added to the human race. 

 As we had occasion to remark in the case of or- 

 ganisms generally (quoting Mr. Herbert Spencer), 

 increased difficulty of life-conditions necessitates in- 

 creased evolution, and this is true for man's mental 

 progress as for general structural progress. Were 

 the evolution not always in advance of the provoking 

 cause, we might anticipate the extinction of humanity 

 by the excessive competition and excessive difficul- 

 ties of existence which must accompany increased 

 population. More justly, as it appears, and more 

 hopefully, we may look forward to a time when, the 



