THE RATE OF AGEING IN 

 DROSOPHILA SUBOBSCURA 



J. IVIaynard Smith 



Department of Zoology, University College London 



To a geneticist, the oddest feature of gerontology is the 

 absence of a coherent and generally accepted theory of age- 

 ing, comparable to the chromosome theory of heredity. In 

 case this remark should cause any misgivings, it should be 

 said that no attempt will be made to remedy this defect. 

 Instead, two kinds of theory which seem to be possible will 

 be indicated, since this will help to interpret some experiments 

 to be described later. 



We have to accept that a theory of ageing may be valid 

 only for a single species or group of related species. It may 

 be that we shall find a theory which proves to have the same 

 universality in the study of ageing as does the chromosome 

 theory in genetics, but this does not at present seem very 

 likely. What kinds of theory, then, can be put forward to 

 explain ageing in a single species, say in men or in mice or in 

 fruitflies? A distinction should be made between two types of 

 theory, which may be called "single" and "multiple" theories 

 of ageing. 



A multiple theory would postulate that there are a number 

 of partially independent processes occurring in every in- 

 dividual, any one of which may ultimately cause death. It 

 is not intended to imply that two processes in a single in- 

 dividual can ever be wholly independent; by "partially 

 independent" is meant only that each process would continue, 

 perhaps at an altered rate, in the absence of the others. Now 

 some ageing processes are fairly certainly independent in this 

 sense. For example, the mechanical wearing away of the 

 teeth of herbivorous mammals would occur even if other 



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