AN ESSAY ON LONGEVITY. 95 



but variation in the longevity of groups characterized 

 by different habits, food, &c., and it is not to the 

 race of men, but to the difference of conditions in 

 which they Hve, that we must direct our attention. 

 As was stated above, man's brain by its adapting 

 power makes the essential conditions of life much 

 more nearly uniform than would at first be sup- 

 posed from his varied habitat, the total expendi- 

 ture in procuring heat, food, safety, and in repro- 

 duction together being about the same in most 

 races and classes. Hence we do not look for much 

 difference of longevity, even in different climes and 

 different civilizations. It is when we come to ex- 

 tremes, however, such as do exist, in which men 

 are living and not adequately contending with nature 

 by their intelligence, but are getting worsted in the 

 struggle, that we may expect appreciable variation in 

 longevity ; the expenditure is increased in one direc- 

 tion without being diminished in another, and con- 

 sequently the longevity suffers.^ Thus, whilst the 

 savages of Polynesia and of many parts of Africa, 



' The inhabitants of Iceland are stated to rarely attain old age, com- 

 paratively few reaching the age of sixty, but I have not found any statis- 

 tical proof of this assertion. (' Aitken's Medicine,' vol. ii.) In the same 

 virork the terrible condition of the inhabitants of the Pontine Marshes is 

 described from various sources, arid it is clearly shewn that men living 

 in such malarious conditions have life greatly curtailed, becoming old 

 and exhausted before other men have reached their prime. These cases 

 appear to be abnormal in their conditions of life, and no evidence is 

 forthcoming as to whether hereditary diminution of longevity is brought 

 about by the subjection of a population to such circumstances. Prob- 

 ably it is. 



