il 



I 

 THE UNIQUENESS OF THE INDIVIDUAL l 



we call the senile state is in the ecologist''s sense merely patho- i 

 logical. Senility is an artifact of domestication, something dis- \ 

 covered and revealed only by the experiment of shielding an 

 animal from its natural predators and the everyday hazards of ' 

 its existence. In this sense, no form of death is less ""naturar '' 

 than that which is commonly so called. ] 



Some interesting conclusions may be drawn from the fact I 

 that the latter end of life is ecologically atrophic or vestigial. i 

 It has several times been pointed out^ that the changes which j 

 an animal may undergo after it has ceased to reproduce are 

 never directly relevant, and are in most cases quite irrelevant, 

 to the course of its evolution. A genetic catastrophe that befell 

 a mouse on the day it weaned its last litter would from the 

 evolutionary point of view be null and void. This state of 

 affairs is tacitly acknowledged in the celebrated half-truth that 

 'parasites live only to reproduce"*: the whole truth is that what 

 parasites do after they reproduce is not on the agenda of 

 evolution. The same applies to what may befall a mouse when it 

 reaches the age of three, though in fact it never (or hardly ever) 

 lives that long. We shall return to this point later. For the 

 present it may be said that the existence of a post-reproductive 

 phase of life is not causally relevant to the problem of ageing, 

 for it is just that very ingredient of the ageing process — the 

 decline and eventual loss of fertility — which it is our chief 

 business to explain. 



What is the upshot of all this speculation? I think many 

 biologists would agree that Weismann was in principle correct, 

 and that the process of senescence in the individual and the 

 form of the age-frequency distribution of death that mirrors 

 it statistically have been shaped by the forces of natural 



^ Cf. G. G. Simpson, Tempo and Mode in Evolution^ p. 183, Columbia 

 University Press, 1944. 



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