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DISCUSSION 



Danielli: The simplest physical interpretation of your regression 

 equation, Mr. Sacher, is that it is an advantage to have a brain, and 

 a disadvantage to have a body ! 



Wigglesworth: Barcroft's thesis (Barcroft, J. (1934). Features of 

 the Architecture of Physiological Function. Cambridge University 

 Press) was that a constant internal environment was primarily 

 essential for the functioning of the brain, and that for higher 

 development of the brain you needed a more constantly regulated 

 internal environment. As I understand your theory, that same 

 constancy will also be favourable to longevity, so that cephalization 

 and longevity should go hand in hand. 



Verzdr: Do you not think that lifespan as a measurement of ageing 

 trends is a bad measurement, Mr. Sacher ? Lifespan is the most un- 

 certain of all our records. The mortality curves are not straight ; 

 they are always an "S " shape, and the right side of that "S " shape, 

 especially, is extremely long, so that exceptionally long lives are 

 particularly noticed. Wouldn't it be much better to relate all our 

 age theories not to the maximal lifespan, but to something like a 50 

 per cent survival of a certain population ? That would make the 

 whole thing experimentally much more certain. 



Sacher: I agree that maximum lifespan is a gross measure. That it 

 is a bad measure I would not agree. Lifespan is an extremum statis- 

 tic, and can be handled in a perfectly rigorous fashion by statistical 



