Relation of Lifespan to Brain and Body Weight 127 



Table I 



Lifetime energy expenditure (cal./g.) for several, species 



OF DOMESTIC ANIMALS AND MAN (FROM RUBNER, 1908) 



Species 



Horse 



Cow 



Dog 



Cat 



Guinea pig 



Man 



Body Wt. 



kg. 



450 



450 



22 



3 



0-6 

 70 



Length 



of 

 life 



(years) 



30 

 26 



9 



8 



6 

 100 



Lifetime 



energy 



expenditure 



(cal./g.) 



170,000 

 141,000 

 164,000 

 224,000 

 266,000 

 800,000 



allometric analysis. I had been working on a theory of 

 mortaHty and ageing which took particular cognizance of the 

 role played by physiological fluctuations (Sacher, 1956, 1958). 

 The essential points of this theory are : 



(a) mortality is essentially a random process in that the 

 circumstances leading to death in an individual case cannot be 

 predicted with certainty ; 



(b) the physical basis for this uncertainty is to be found in 

 the fluctuations of physiological state that are inevitably 

 present in living systems; and 



(c) the magnitude of the physiological fluctuations is 

 determined by the interplay between the random impinging 

 disturbances (of external and internal origin) and the regula- 

 tory mechanisms that act to limit the magnitude and duration 

 of their effects on the organism. 



A central problem in the mathematical development of the 

 theory is that of deriving the quantitative dependence of the 

 probability of mortality in given circumstances on the para- 

 meters of the physiological fluctuation process. The important 

 implication of the theory in the present context is that the 

 attainable length of life for a species depends on the precision 

 of physiological regulation that the species is capable of. 

 The logical or mathematical developments that lead to this 



