AN ESSA Y ON LONGEVITY. 53 



not get increased evolution, but rather the reverse 

 process ; on the other hand, if we may assume the 

 theory of progressive development of species, it is by 

 a decreased accessibility of food that higher evolution 

 is brought about, new developments, fresh powers 

 and activities, being originated to cope with the 

 increased difficulties, and this results in such a gain 

 to the individual,' that food may become more abun- 

 dant to it in its improved structure than it ever was 

 before ; in this case, the species survives and becomes 

 dominant. In this case, clearly, the apparent dimi- 

 nution of food becomes in reality an increase, and 

 thus again in the equation fertility x average lon- 

 gevity x potential longevity=foodx<^, the change in 

 the quantity 'food,' as well as the diminution in 

 'fertility' necessarily accompanying increased indi- 

 viduation, is counterbalanced by the increased lon- 

 gevity accompanying increased individuation. Diffi- 

 cult and deeply involved as the analysis here attempted 

 is, and especially hard to discuss without entering into 

 much detail (already fully treated by Mr. Spencer, 

 but not in relation to longevity) — yet the above 

 outline may serve to shew why it is that the relations 

 which we have seen reason to believe, do exist for 

 longevity, should exist. 



^ Mr. Spencer shews that the increase of individuation is greater than 

 the increased difficulties which call it forth, and that thus there is a 

 surplus of power to the evolved form, which may make itself seen in 

 a greater fertility (or we may add, a greater longevity) than a direct 

 ratio of individuation would admit. 



