Entropic Contributions to Mortality and Aging 329 



The mortality rate for the same model system. 



-m 



e 2a2,(;>3(;) (15a) 



is also an increasing function of a'-, for the exponential factor in equation (15) 



varies much more strongly with g than does the constant factor -. The effect 



of accumulating errors will be to reduce A and jS and to increase a (see above, 

 Section IV). All of these changes tend to increase the mortality rate as age 

 increases. Therefore it is concluded from this quahtative discussion that the 

 mortality rate of different species, and the rate of increase of mortality rate with 

 age for the same species are positively correlated. There are too many uncertain- 

 ties to pemiit a statement of the functional relation between these quantities at 

 present. However, we have here a possible basis for the relative constancy in the 

 form of the life table for species as widely different as fruit fly, mouse and man. 

 The total error rate includes all three terms discussed above 



£total = fr + ^.1/ + ^F (43) 



where the subscripts denote temperature, metabolic rate and fluctuation, 

 respectively. The existence of contributions to the error rate arising from back- 

 ground ionizing radiations and other environmental noxae must also be acknow- 

 ledged. Perhaps the best viewpoint is that the physical basis for each term 

 demonstrably exists, but we do not know the absolute contribution of any of 

 them. This will be a major experimental problem. 



All of these contributions arise when the environment and the population 

 are in a steady state of fluctuation. The course of aging is also influenced to an 

 important extent by very large disturbances that occur infrequently in the 

 lifetime of the individual. Illness and crippHng accident are examples, but 

 changes of nutrition, etc., have equally important effects, as do also insults 

 such as adventitious poisoning. The unique nature of these events requires 

 that they be treated historically rather than on the basis of statistical uniformity 

 of occurrence. Under experimental conditions it can be shown that exposure 

 of a population to ionizing radiations leaves a pennanent residue of injury (7). 

 Jones (18) has demonstrated that human sub-populations selected on the basis 

 of a history of given diseases have a permanent increase in their mortality at 

 later ages. Some writers have attributed aging in general to the action of such 

 major disturbances. Against this position it can be argued that the large common 

 factor in the aging of human or animal populations points to an agency that 

 acts with comparative uniformity on all members of the population and within 

 each individual over the course of life. This is compatible with the statistical 

 uniformities that appear in the summation of a large number of small indepen- 

 dent events as proposed herein. 



REFERENCES 



1. W. B. Cannon: Organization and physiological homeostasis. Physiol. Rev. 9, 399-431 

 (1929). 



2. C. L. Prosser: Physiological variation in animals. Biol. Rev. 30, 229-262 (1955). 



