AN ESSA Y ON LONGEVITY. 8t 



material. This we see in the greater length of life 

 of carnivorous and frugivorous animals as compared, 

 cceteris paribus, with herbivorous and garbage-eaters. 

 This reduces itself to a case of evolution and bulk ; 

 for in the first group it is an advantage to be large 

 and highly endowed, to be swift and powerful, and 

 to secure the whole mass by one effort. In the 

 second group, five mouths will take in more nutri- 

 ment than one, it being equally diffused ; and hence 

 it is better for a given bulk of the species to be 

 divided into five small individuals than retained in 

 one large one. Where the acquisitive power in- 

 creases more nearly with the bulk, as in vegetals, 

 such a distinction does not hold. It is in ac- 

 cordance with this relation of bulk to food that 

 insects which feed on widely -spread vegetable 

 juices, or similarly wide-spread garbage, are shorter 

 lived than the birds which .prey on the insects, or 

 than other insects which are carnivorous ; and that 

 the lower animals, generally feeding as they do on 

 diffused food, are shorter lived. Thus the frugiv- 

 orous apes are longer lived than other animals similar 

 to them in many other matters which are not fruit- 

 eaters ; carnivora generally than herbivora, in the 

 various classes and orders, cceteris paribus. 



Another apparently important influence in longe- 

 vity is what Mr. Spencer calls ' tertiary aggregation.' 

 This is obviously only a form of increased evolution. 

 Mr. Spencer supposes that what has been somewhat 



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