368 THE BIOLOGY OF THE SEASONS 



a century in captivity, of course, which would lessen their 

 expenditure of energy. 



The clergy have longer lives than other professional 

 men, but most of them live a very active life. St. Antony 

 did not mix much in practical affairs and died at one 

 hundred and five ; Titian was all his life about a court, 

 and painted a fine picture at ninety-six. 



Perhaps the most astounding fact in regard to human 

 length of life is that brought out in such statistical researches 

 as those of Tarchanow, that throughout the world from 

 equator to poles the duration of life remains on the average 

 the same. This is an astounding fact when we consider 

 the diversity of race, of diet, of occupations, and of sur- 

 roundings. There are short-lived and long-lived families, 

 for longevity is hereditary ; there are life-sparing and 

 deathful occupations and habits ; there are pleasant and 

 unwholesome surroundings ; yet the average duration of 

 life for different peoples and countries is about the same. 

 This makes us feel that the punctuation of the length of 

 life, which is so diverse among individuals, is, as regards 

 the species, referable to much wider issues than the im- 

 mediate surroundings, diet, habits, or rate of life. We 

 see no alternative to the conclusion that the clock of 

 human life has been regulated in the course of the ages 

 in reference to the wide issues which we sum up in the 

 conception " the welfare of the species." 



We have expounded a general reason why higher 

 organisms must grow old : the perfect self-repairing 

 capacity of the unicellulars is no longer possible when 

 the bodily mechanism is very complex and when repro- 

 duction is physiologically expensive. But this natural 

 interpretation of senescence fails to suggest why a dozen 

 different kinds of animals of about the same size and 

 complexity, and with similar modes of reproduction, should 



