300 Group Discussion 



desynchronize some of the processes which may be synchronized. It 

 may be in this connexion that we could make some progress by 

 studying systems in which one is normally dealing with symbiosis. 

 Here the breaking-up of the symbiotic relationship might reveal 

 phenomena which would be difficult to reveal by any other method. 



A cellular approach to ageing would under certain circumstances 

 facilitate examination of the actual process of ageing, if this is in 

 fact to some degree unitary, but I am not convinced that this is so 

 with higher animals. The ageing process in higher animals may be 

 fundamentally a function of the complex of cells and operate at a 

 higher level of organization than is present in cells. 



Another point which we have not discussed yet, but which we are 

 probably all agreed upon, is that it is quite possible that lifespan in 

 man, as we see it now, is an entirely accidental by-product of 

 selection for breeding efficiently at a much earlier age, and does not 

 in any sense correspond to social needs of the moment. An accumu- 

 lation of experience has become much more important, or at any 

 rate equally as important as physical vigour; therefore socially 

 speaking there is a very good case for anything which will enable us 

 to modify the expectation of life in a radical manner. Looking at 

 this from the long-term point of view, I think the possibilities for so 

 doing would in fact be good by chemical means, provided ageing 

 does in fact occur by a unitary process. If on the other hand it is 

 due to a very large number of non-unitary processes which do not 

 have any common mechanism, then I think the chemical approach to 

 extension of lifespan is fraught with so many difficulties that it is 

 hardly worth considering. To illustrate the order of magnitude which 

 I would expect if there is a unitary process involved, I would like to 

 refer briefly to the rate of mutation, or rather the rate at which 

 damage is caused by radiation. It is of course a tenable hypothesis 

 that somatic mutation is, one way or another, directly concerned 

 with the ageing process. There are cells which are killed by a dosage 

 of the order of 100 r. ; there are other cells which require a dosage of 

 1,000,000 r. to kill them. This difference of four orders of magnitude 

 is not at present, as far as I know, accountable for in any cytological 

 or physiological terms whatever. Therefore, if ageing were associ- 

 ated primarily with somatic mutation, or some other generalized 

 mechanism of this type, we might expect that under suitable con- 

 ditions lifespans could be varied by that order of magnitude. This 

 sounds a little like science fiction, but all of us have seen so much of 

 what we regarded as science fiction 20 years ago turning up as 

 reality, that I think we must envisage the possibility that we may be 

 able to make radical changes in lifespan. 



