The Biology of Senescence 



mechanical systems also deteriorate with the passage of time. 

 He appears at a later age to derive some degree of comfort from 

 the contemplation of the supposed generality, universality and 

 fundamental inherence of ageing — or alternatively from draw- 

 ing a contrast between Divine or cosmic permanence and his 

 own transience. However inspiring this type of thinking may 

 have been — and it features largely in the past artistic and 

 philosophical productions of all cultures — its influence and its 

 incorporation as second nature into the thought of biologists 

 throughout history has seriously handicapped the attempt to 

 understand what exactly takes place in senescence, which 

 organisms exhibit it, and how far it is really analogous to pro- 

 cesses of mechanical wear. One result of the involvement of 

 senescence with philosophy and the 'things that matter' has 

 been the prevalence of attempts to demonstrate general theories 

 of senile change, including all metazoa and even inanimate 

 objects, and having an edifying and a metaphysical cast. Pro- 

 minent among these have been attempts to equate ageing with 

 development, with the 'price' of multicellular existence, with 

 hypothetical mechano-chemical changes in colloid systems, 

 with the exhaustion induced by reproductive processes, and 

 with various concepts tending to the philosophical contempla- 

 tion of decline and death. 



It is not unreasonable to point out that these theories have 

 for the most part deeper psychological and anthropological 

 than experimental and observational roots. Some of them have 

 a few facts on their side. 'Reproductive exhaustion' does appear 

 to induce senescence in fish and in mollusca, and flowering is 

 a proximate cause of death in monocarpic plants, but the general 

 concept, especially when it is made a universal, owes a large 

 debt to the widespread belief in human cultures that sexuality 

 'has its price'. Extensions of mechanical analogies from the 

 wearing out of tools to the wearing out of animal bodies are 

 justifiable in a limited number of cases where structures such 

 as teeth undergo demonstrable wear with use, and where this 

 process limits the life of the organism; but they have also shown 

 a tendency to become generalized in the hands of biologists 

 who are devoted for philosophical, political or religious reasons, 

 to mechanism in the interpretation of human behaviour. State- 



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