72 MAN THE ANIMAL 



pations have been deducted. This relation is of the sort that 

 associates high mortality with hard physical labor. The relation- 

 ship prevails whether the labor is performed chiefly indoors or 

 chiefly outdoors, Figure 14. 



It is not primarily to be attributed to the general environ- 

 mental factors connoted by social class distinctions, which are 

 themselves correlated with average energy expenditure in occu- 

 pation. Before age forty is attained, it makes no difference in 

 the rate of mortality whether the occupation involves light or 

 heavy physical labor. After roughly age forty to forty-five it 

 appears that the average duration of human life is shortened, 

 by definite amounts, in proportion as physically heavy labor is 

 performed. 



The literature of longevity is full of advice, recipes, and pre- 

 cepts for the attainment of long life. These precepts touch upon 

 nearly every conceivable aspect of personal physiology and 

 hygiene. Yet it is an odd fact that careful study of our collec- 

 tion of life records of nonagenarians and centenarians leads, as 

 one of the broadest generalizations it is possible to make from 

 them, to the conclusion that these 2000 and more persons ex- 

 hibited substantially the same range and degree of variation 

 relative to these various items of personal hygiene as is found 

 amongst people in general. Some were light eaters, others on 

 the gluttonous sidej some used tobacco, others didn't; some 

 drank heavily, others moderately, while still others were tee- 

 totalers; some slept a lot, others didn't; some had been in 

 robust health all their lives, others had been ailing a great part 

 of the time; and so on. In only one outstanding respect besides 

 great longevity did the group markedly differ from the gen- 

 erality of mankind, on the whole. That is in the fact that a vast 

 majority of these extremely longevous folk were of a placid 

 temperament, not given to worry. They had taken life at an 

 even, unhurried pace. In this respect this human material agrees 

 with and confirms a generalization that has emerged from ex- 

 perimental studies on life duration. It is that the length of life 

 is generally in inverse frofortion to the rate of living. The more 



