CHAPTER VI 



ONTOGENESIS 



THERE is no reason, a priori, why the individual 

 plant or animal, barring accident, should not live 

 forever. We can conceive of a perfectly balanced 

 metabolism in which the up-building or tissue- 

 repairing process would exactly balance the dis- 

 ruptive or tearing-down process. As a matter of 

 fact we know of no form, even among the simplest, 

 of which this is true. In all, katabolism after a 

 certain time tends to exceed anabolism. In spite of 

 Nature's wonderful recuperative powers, the living 

 organism, like a machine, tends to wear out, and after 

 a brief period is fit only for the scrap-heap. 



Competition, the " struggle for existence," is 

 severe among different species, and a species that is 

 able to replace frequently its worn-out members with 

 vigorous new individuals would maintain its level 

 of efficiency, so to speak, at the highest point. More- 

 over, where numbers count so heavily, the species 

 that might be able to replace each worn-out veteran 

 with a hundred or a thousand new recruits, would 

 have a corresponding advantage over one that could 

 not do so. 



Whether or not some such conditions as these may 

 have been the cause, they indicate, at any rate, an 



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