CHAPTER VI 



THE INHERITANCE OF DURATION OF 



LIFE IN MAN 



WE have seen that in the case of man, where alone 

 quantitative data are available, the breakdown of partic- 

 ular organ systems, and consequent death of the whole, 

 occurs in a highly orderly manner in respect of time or 

 age. Each organ system has a characteristic time curve 

 for its breakdown, differing from the curve of any other 

 system. The problem which now confronts us is to find 

 out what lies back of these characteristic time curves and 

 determines their form. In view of the biological facts 

 about death which we have learned, what determines that 

 John Smith shall die at 58, while Henry Jones lives to 

 the obviously more respectable age of 85? We have 

 seen that there is every reason to believe that all the 

 essential cells of both their bodies are inherently capable 

 under proper conditions of living indefinitely. It fur- 

 ther appears probable that it is the differentiated and 

 specialized structure of their bodies which prevents the 

 realization of these favorable conditions. But all this 

 helps us no,t at all to understand why in fact one lives 

 nearly 30 years longer than the other. 



It may help to visualize this problem of the determina- 

 tion of longevity to consider an illustrative analogy. 

 Men behave in respect of their duration of life not unlike 

 a lot of eight-day clocks cared for by an unsystematic 

 person, who does not wind them all to an equal degree 

 and is not careful about guarding them from accident. 

 Some he winds up fully, and they run their full eight days. 



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